Growth and Biodegradation by Sporidiobolales Yeasts in Vanillin

Home , Rhodotorula, Sporidiobolales, Sporidiobolus, Sporobolomyces

AKADEMIN FÖR HÄLSA OCH ARBETSLIV Avdelningen för arbets- och folkhälsovetenskap

Growth and biodegradation by Sporidiobolales

yeasts in vanillin-supplemented medium

Natalia González Gaarslev

2017

Examensarbete, G2E, 15 hp Biologi Examensarbete i Biologi

Handledare: Sandra A. I. Wright Examinator: Mikael Lönn

Summary

Studies of biodegradation in lignins by basidiomycetes yeasts show the conversion of lignin in various degradation products among which vanillin, a valuable substance, suggested to be a strong inhibitor of both fermentation and growth of yeasts, stands. Sporidiobolales yeasts used in these experiments were aimed to be identified by their highly conserved ITS region as well as studied in vanillin- supplemented medium through, vanillin-supplemented plates, TLC and Neubauer’s chamber to find out which, among the several isolates tested, were the most resistant ones, understand how they take up vanillin and how their growth is affected by the presence of the phenolic compound. Two strains were identified as Rhodotorula babjevae. One of them, L4, together with LS22, Rhodosporidium kratochvilovae, could withstand and biodegrade high concentrations of vanillin, producing biodegradation products with Rf values similar to the ones know for vanillic acid and vanillyl alcohol. Better growth in medium supplemented with small doses of vanillin was found, as well as disparity among the same species and their metabolic features, therefore, herbicides resistance was suggested as a reason for strains divergence. Further morphological-species comparison could also describe if there exist a relation between them. Resumen Estudios sobre la biodegradación de ligninas por levaduras basidiomicetes muestran la conversión de lignina en distintos productos de degradación, entre los cuales se encuentra la vainillina, un fuerte inhibidor de la fermentación y el crecimiento de levaduras. Las levaduras Sporidiobolales utilizadas en estos experimentos han intentado ser identificadas a través de la región ETI, muy conservada, además de estudiadas en medios suplementados con vainillina mediante placas suplementadas con vainillina, CCF y cámara de Neubauer para averiguar cuáles son las cepas más resistentes, entender cómo metabolizan la vainillina y cómo su crecimiento se ve afectado por la presencia de dicho compuesto. Dos cepas fueron identificadas como Rhodotorula babjevae. Una de ellas, L4, junto con con la cepa LS22, Rhodosporidium kratochvilovae, pudieron soportar y biodegradar elevadas concentraciones de vainillina, originando productos de biodegradación con valores de Rf similares a los del ácido vanílico y alcohol vanílico previamente conocidos. Se encontró un crecimiento mejor en medios suplementados con pequeñas dosis de vainillina además de una disparidad entre mismas especies y sus características metabólicas, así, herbicidas han sido sugeridos como una posible causa en dicha divergencia. Una futura comparación morfología-especie podrá describir si existe relación entre ambos.

Key words/Palabras clave: Sporobolomyces/Sporobolomyces, Vanillin/Vainillina, Internal Transcribed Spacer (ITS)/Espaciador Transcribible Interno (ETI), Thin layer chromatography (TLC)/Cromatografia en capa fina (CCF), Neubauer’s chamber/Cámara de Neubauer.

Contents Summary ...... 2

1. Introduction ...... 2 1.1. Background ...... 2 1.1.1. Lignin, an abundant organic polymer in Earth ...... 2 1.1.2. Vanillin as a biodegradation product from lignin ...... 2 1.1.3. Biodegradation of vanillin by microorganisms ...... 3 1.1.4. Sporidiobolales yeasts ...... 3 1.1.5. Ecological uses of Sporidiobolales yeasts ...... 4 1.1.6. Methods of identification of fungi ...... 4 1.2. Aims, objectives ...... 4 2. Materials and methods ...... 5 2.1. Culture media ...... 5 2.1.1. Yeast extract-peptone-dextrose (YEPD) ...... 5 2.1.2. Lilly-Barnet, LiBa (Lilly VG, 1951) ...... 5 2.1.3. LiBa-Vanillin (VA) stock solution 0.1 M ...... 5 2.2. Yeast collection ...... 5 2.3. Identification experiments ...... 7 2.3.1. Genomic DNA extraction ...... 8 2.3.2. Polymerase chain reaction (PCR), amplification of ITS regions ...... 10 2.3.3. PCR product classification ...... 11 2.3.4. Purification of the PCR product gel bands ...... 11 2.3.5. Verification of an adequate amount of DNA in the samples ...... 12 2.3.6. Preparation of sequencing samples ...... 12 2.3.7. Sequencing ...... 12 2.3.8. Identification ...... 13 2.4. Vanillin resistance experiments ...... 13 2.4.1. Selection test of the most resistant isolates ...... 13 2.4.2. Vanillin resistance and degradation in liquid cultures ...... 14 2.5. Yeast growth in vanillin supplemented medium ...... 15 2.5.1. Cell count in Neubauer’s chamber ...... 16 3. Results ...... 16 3.1. Identification experiments ...... 16 3.1.1. DNA extraction ...... 16 3.1.2. PCR product ...... 16 3.1.3. Gel elution and recovery of purified ITS fragments ...... 18 3.1.4. Verification of required minimum concentration of template DNA ...... 18 3.1.5. Identification results ...... 18 3.2. Vanillin experiment: selection of most vanillin resistant isolates ...... 19 3.3. Vanillin biodegradation in liquid cultures, TLC results ...... 20 3.4. Vanillin resistance: Neubauer’s chamber results...... 22 4. Conclusions and discussion ...... 23

5. References ...... 24

1. Introduction 1.1. Background

1.1.1. Lignin, an abundant organic polymer in Earth Lignin is a high molecular weight three-dimensional macromolecule (Hedges & Mann, 1979), a complex heteropolymer (Campbell & Sederoff, 1996) synthesized in vascular plants through the dehydrogenative polymerization of three cinnamyl alcohols: 4- hydroxycinnamyl alcohol, coniferyl alcohol and synapyl alcohol (Boudet, et al., 1995) . Lignin is the main structural component in plants secondary wall (Guo, et al., 2001) being deposited in wall cells at the last stages of their differentiation (Boudet et al., 1995). Besides mechanical support, lignin plays a significant role in both water transport and defence in vascular plants (Campbell & Sederoff, 1996). Vascular plants, mainly constituted of lignin, cellulose and hemicellulose (Demain, et al., 2005) when dead, remain in the environment as lignocellulosic biomass, considered a natural renewable resource due to its abundance (Demain et al., 2005). Lignin, therefore, is one of the most abundant polymers in nature (Fengel & Wegener, 1984) and due to its non-water solubility and optical inactivity, the study of its degradation is very complicated (Fengel & Wegener, 1984). Lignin is known to be very resistant to microbial degradation (Higuchi, 1990). Studies of biodegradation in decayed wood lignins by whiterot basidiomycetes groups (Hata, 1966; Kirk & Chang, 1974) show the conversion of lignin in several degradation products among which vanillin, considered a valuable substance, stands (Henderson, 1961; Higuchi, 1981; Zimmermann, 1990).

1.1.2. Vanillin as a biodegradation product from lignin

Vanillin (4-hydroxy-3-methoxybenzaldehyde), is the major component of natural vanilla (Walton, et al., 2003), widely used for flavouring food, aromatise perfumes and it can also intervene in pharmaceuticals synthesis (Voitl & Rohr, 2009). Considered a valuable substance, vanillin can be synthetically produced from lignin, obtained from the black liquor produced in Kraft processes in pulp and paper industry (da Silva et al., 2009) and its scale production began in 1936 in the United States (Hocking, 1997).

1.1.1.1 Vanillin toxicity Vegetal substances used as flavouring agents, like vanillin, are known to possess antimicrobial activity, being suitable in products conservation (Beuchat & Golden, 1989; Jay & Rivers, 1984). Vanillin is an antimycotic substance (Beuchat & Golden, 1989) which can used in food preservation, reducing thus the addition of non-natural preservatives. Vanillin is known as a strong inhibitor of fermentation and growth of yeasts as it has been studied in the fermentation of lignocellulose hydrolysates, in bioethanol fermentation, and it acts in very low concentrations (Endo, et al., 2008). 1.1.3. Biodegradation of vanillin by microorganisms Biodegradation of vanillin, among several wood hydrolysates, has been studied with the basidiomycete fungus Trametes versicolor (Jönsson, et al., 1998) as well as with the yeast Saccharomyces cerevisiae, a good resistant to inhibitory compounds (Palmqvist, et al., 1998). Clostridium methoxybenzovorans sp., an anaerobic, spore-forming bacterium has also shown to be a good degrader of methoxylated aromatic compounds (Mechichi et al., 1999). The tolerance of vanillin by the yeast Rhodosporidium toruloides, a Sporidiobolales yeast, has been studied, providing novel mutant strains to optimize biofuel production from lignocellulosic biomass (Qi et al., 2014). In this project, the behaviour in vanillin-supplemented medium of red coloured yeasts belonging to the class Uredinomycetes, order Sporidiobolales is studied.

1.1.4. Sporidiobolales yeasts

Sporidiobolales order belongs to Puccinimycotina subphylum, in Basidiomycota division and pertains to Uredinomycetes class, including the genera Rhodotorula p.p., Sporidiobolus, Sporobolomyces p.p. and Rhodosporidium (Sampaio, et al, 2003). Sporidiobolales yeasts or “red yeasts”, named due to their production of carotenoid pigments, which provide them of a characteristic colour (Kurtzman, et al., 2011), can be easily cultivated and are worldwide distributed (Aime et al., 2006). Thirty-nine strains of basidiomycetes red yeasts in their asexual unicellular state (Sampaio et al., 2003), belonging to a larger collection created at the Department of Plant Pathology at the University of Molise in 2008 (Palmgren, L., 2009), are used to carry out this project. The strains had undergone preliminary investigations based on its 3

morphological characterization as well as their study as biocontrol agents of fungal pathogens of plants and fruits (Castoria, et al., 2003; Castoria et al., 2005; Lima, et al., 1998).

1.1.5. Ecological uses of Sporidiobolales yeasts

Sporidobolales yeasts have a wide range of usages such as: studies in tarball (weathering of crude oil in marine environments) degradation (Shinde, et al, 2017), their usage as biocontrol agents of fungal pathogens of plants and fruits (Castoria et al., 2003; Castoria et al., 2005; Lima et al., 1998), carotenoid production (Yurkov, et al., 2008) for colorants in animal feed, ubiquinone q10 production for antioxidants (Yurkov et al., 2008) and vanillin biodegradation studies (Qi et al., 2014) for environmental cleaning.

1.1.6. Methods of identification of fungi

Fungi, even though they are the second largest kingdom of eukaryotic life (Blackwell, 2011) have not a primary DNA barcode marker. The internal transcribed spacer (ITS) region seems to be the DNA region with the highest probability of success in identification in the broadest range of (Schoch et al., 2012). Internal transcribed spacer (ITS) region is has two variable non-coding regions nested within the rRNA repeat between the 5.8S subunit and genes of the large rRNA subunit (Gardes & Bruns, 1993). Features such as the amount of base pairs, between 600 and 800 when using primers ITS5 and ITS4 (White, et al., 1990), or the fact that it is a very conserved sequence within species (Scorzetti, et al., 2002) make them a perfect target to be amplified with “universal primers” (White et al., 1990). ITS regions are a convenient region for molecular identification of fungi (White et al., 1990). Several studies have demonstrated the variability of ITS regions according to morphological distinction in fungal species (Gardes, et al., 1991; Gardes & Bruns, 1993).

1.2. Aims, objectives This project has two main objectives. The first one is to test 39 different strains of yeasts belonging to the order Sporidiobolales searching for the most resistant ones growing in increasing concentrations of vanillin. The ones that grow better are selected to study how they take up vanillin during their development, both through the yeast growth and vanillin biodegradation pathway. The second objective aims accomplish and

optimize several genomic experiments to identify the tested yeasts which can be reproduced to identify more Sporidiobolales yeasts. 2. Materials and methods 2.1. Culture media

2.1.1. Yeast extract-peptone-dextrose (YEPD)

YEPD is a rich medium for yeast growth. Two different variants have been used, liquid YEPD with glycerol, to prepare samples for a frozen backup, liquid YEPD to grow the strains before the DNA extraction process and solid YEPD, with agar in a concentration of the 2%, for petri dishes. To prepare one litre the solution contains 3.0 g Yeast extract, 10 g peptone of casein, 10 g D-glucose and 20 g bacteriological agar.

2.1.2. Lilly-Barnet, LiBa (Lilly VG, 1951)

LiBa medium is a minimum growth medium developed to study fungi strains features such as carbon nutrition and physiology, concluding that structural variation and configuration of carbon molecules compounds affect to the way in which fungi utilize them (Lilly VG, 1951). In the present study, the amount of the different compounds integrating the medium vary from the original formula as follows, containing in one litre: 10.32 g of D-glucose, 2.0 g of L-asparagine, 1.0 g of KH₂PO₄, 0.5 g MgSO₄ x 7H₂O, 2 x 10-3 g of FeSO₄ x 7H₂O, 8,7 mg ZnSO₄ x 7 H2O, 4x10-6 mg MnSO₄ x H₂O, 4x10⁴ mg biotin and 4x10-4 mg thiamine LiBa medium was used as liquid LiBa but also as semisolid LiBa (2% agar) on petri dishes.

2.1.3. LiBa-Vanillin (VA) stock solution 0.1 M

A stock of LiBa-VA 0.1 M was used in all the vanillin-supplemented experiments to adjust concentrations of LiBa-VA 1 mM, LiBa-VA 5 mM and LiBa-VA 10 mM. To prepare 10 ml of stock solution, 0.512 g of vanillin were necessary.

2.2. Yeast collection Concrete strains (Table 1) belonging to the collection created in 2008 in of University of Molise (Palmgren, L., 2009) were selected due to their not reliable identification in a first attempt. For this reason, some of them have a species name between quotation

marks (“ ”). The execution and optimization of this experiments will lead to a forthcoming identification of the isolates. The yeast strains used in this project were sampled from different vegetal species in different climatic zones in central-southern Italy: Larino, Isole Tremiti, Campomarino, Petacciato, Castel San Vincenzo and Portocannone (Curtis F, et al., 2009; Curtis, et al., 2009; de Curtis et al., 2010). All the isolates were conserved in 40% glycerol YEPD at - 80 ºC.

Table1: Collection and reference strains: locations and plants where the different strains were sampled strain numbers, collection number designated in Italy and the number assigned to the tubes in the frozen backup in Sweden. The table cells highlighted with a light grey background indicate the reference strains. Italian number Strain number Plant of origin Place isolated Frozen number 1 L2 Unknown Unknown F37 3 L4 Unknown Unknown F2 13 L105 Malus domestica Larino F3 36 L151 Ficus carica Larino F1 37 L153 Olea europea Larino F32 38 L154 Olea europea Larino F4 39 L155 Olea europea Larino F5 40 L156 Olea europea Larino F6 42 L160 Olea europea Larino F38 47a L166A Malus domestica Larino F7 52 L177 Malus domestica Larino F39 58 L200 Ficus carica Larino F8 60 L206 Ficus carica Larino F35 62 L209 Prunus persica Isole Tremiti F9 67 L215 Prunus persica Isole Tremiti F10 74 L234 Unknown Unknown F11 79 L241 Rosmarinus Molise coastal F12 officinalis 114 L384 Ficus carica Isole Tremiti F36 118 L388 Unknown Unknown F31 119 L389 Unknown Unknown F13 194 L212 Unknown Unknown F17 195 L400 Unknown Unknown F18 196 L411 Olea europea Isole Tremiti F19 83”70” L249 Prunus armeniaca Portocannone F20 87 L257 Pistacia sp. Molise coastal F21 88 L268 Euphorbia paralias Campomarino F22 89 L269 Euphorbia paralias Campomarino F23 98 L359 Crithmum maritimum Isole Tremiti F24 116 L386 Ficus carica Isole Tremiti F34 123 “Rhodotorula sp.” Unknown Unknown F25 124 “Erytrhobasidium Asparagus acutifolia Isole tremiti F26 hasegawianum” “104” L393 Unknown Unknown F27 “105” L394 Asparagus acutifolia Isole tremiti F28 156 L452 Malus domestica Castel San Vincenzo F29

185 L-76-2* Olea europea Larino F33 187 LS11* F30 188 LS22* Solanum tuberosum Venfaro F14 189 LS28* F15 190 Sporobolomyces sp. * F16

All the strains indicated with an asterisk (“*”) were studied before and some of them took part in published experiments. They were used as reference strains. Sporobolomyces roseus / Sporidiobolus sp*. is the isolate L-76-2* in the collection of the Dipartimento A.A.A. dell‟Università degli Studi del Molise”, it was isolated from potato surface (Wright, S. A. I., personal communication). Rhodosporidium kratochvilovae is the isolate LS11* in the collection of the Dipartimento A.A.A. dell‟Università degli Studi del Molise”, it was isolated from olive leaves (Lima et al., 1998), and it is an efficient biocontrol agent against common postharvest pathogenic fungi (Castoria et al., 2003; Castoria et al., 2005; Lima et al., 1998) and an in vitro degrader of the mycotoxin patulin (Castoria et al., 2005). Studies of the phenotypic and genetic heterogeneity of the isolate R. kratochvilovae, have led to a reclassification of the isolate LS11 from Rhodotorula glutinis to R. kratochvilovae (Castoria et al., 2011). Rhodosporidium kratochvilovae is the isolate LS22* in the collection of the Dipartimento A.A.A. dell‟Università degli Studi del Molise”, it was isolated from olive leaves (Wright, S. A. I., personal communication). Cryptococcus laurentii is the isolate LS28* in the collection of the Dipartimento A.A.A. dell‟Università degli Studi del Molise”, it was isolated from Annurca apples (Lima et al., 1998) and it is an efficient biocontrol agent with antagonist activity against B. cinerea and P. expansum in injured apples stored at 3ºC and 20ºC (Lima et al., 1998; Lima, de Curtis, Castoria, & De Cicco, 2003). The strain called Sporobolomyces sp.* in the table is strain IAM 13481 (Valerio, et al., 2008).

2.3. Identification experiments DNA barcoding is a rapid developing alternative in species identification, being nowadays a critical tool in fungal taxonomy (Harrington et al., 2014). The target for the DNA barcoding was the internal transcriber sequence (ITS) region. The results were supported by GenBank database of the US National Centre for Biotechnology

Information (NCBI) using the Basic Local Alignment Search Tool (BLAST). Barcoding projects are of high value for documenting fungal diversity. To identify the isolates, several experiments, such as DNA extraction, Polymerase Chain Reaction and agarose gel electrophoresis and their optimization were carried out in these pigmented yeasts, which we know on beforehand belong to order Sporidiobolales of the class Urediniomycetes (Gadanho & Sampaio, 2005).

2.3.1. Genomic DNA extraction

To study molecular systematics of any organism, high quality DNA is required (Aljanabi & Martinez, 1997). A genomic extraction was completed according to the protocol developed by Hoffman, C. in 2001 (Hoffman, 2001) with specific modifications. One loopful of a single colony of each strain (grown for 24h in a YEPD petri dish) was grown in 5 ml liquid YEPD in a 50 ml falcon tube in a horizontal shaker overnight, at room temperature and 2300 rpm. The shaking allows cells survival enabling them to reach the surface and take the O2 from the environment, fundamental for them to grow. After 24 h, the tube was centrifuged 5 minutes at 4000 revolutions per minute (rpm), the supernatant discarded, and the pellet transferred to an 1,5 ml Eppendorf tube. The tube was frozen for 30 min at -80 ºC, in this step, the cell membranes break due to the mechanical stress caused by the congelation. Subsequently the cells were resuspended in 0,5 mL TENTS buffer (extraction buffer 10 mM Tris HCl pH 7,5, 1 mM EDTA pH 8, 100 mM NaCl, 2% Triton X-100 and 1% SDS) to recover the cell conditions avoiding DNA damage. All buffers containing a detergent, in this case, Sodium-Dodecyl-Sulphate (SDS) lysate the nucleus releasing the DNA. The mixture was transferred to a new autoclaved Eppendorf tube containing the equivalent of 0.2 ml of acid washed glass beads. Later 0.5 ml of phenol-chloroform- amylalcohol (25:24:1) were added to the mixture which was afterwards bead-beated for 15 min in a tabletop bead shaker. Phenol-chloroform-amylalcohol solutions denature the proteins, this, together with the mechanical stress caused by the glass beads and the shaking will divide the solution in an aquose phase (in the upper part of the Eppendorf) containing the DNA, and an organic phase, containing the phenolic and cell residua. On the next step of the DNA extraction cells were frozen for 30 min at -80 ºC, bead-beated other 30 min in a tabletop bead shaker and finally spun at 13000 rpm at room temperature (RT) for 10 min.

The aqueous phase (which contains the DNA) was transferred to new autoclaved Eppendorf tubes and 0.4 ml of isopropanol were added. Isopropanol helps to precipitate the DNA re-establishing its three-dimensional structure. The DNA was precipitated by rocking and spin at 4 ºC at 13000 rpm for 20 minutes and subsequently washed with EtOH 70% (which also precipitates the DNA). Finally, the DNA pellet was dissolved in 0.2 ml double distilled MilliQ water (ddH20 MilliQ) and stored at -20 ºC.

2.3.1.1. RNAse treatment For the procurement of a purer DNA sample, an RNAse treatment was included adding 30 µl of 1 mg/ml DNase-free RNase, which after mixture with the sample was incubated 5 minutes at 37 ºC. Later, 10 µl of 4 M ammonium acetate and 1 ml of 100% ethanol were included in the mixture and mixed by inversion to reprecipitate the nucleic acid. Finally, the tubes were micro-centrifuged 3 minutes at high speed and RT, the supernatant discarded and after the DNA pellet had dryed, this one was resuspended in 100 µl Tris-EDTA (TE) buffer.

2.3.1.2. Verification of DNA’s extraction succeed All DNA samples had to be checked after their setting up to find out if the DNA extraction was successful. Agarose electrophoresis can accomplish this commitment, enabling to see the migration of a charged molecule with high resolution (Lehrach, et al., under the influence of an electric field (Lima Pastrana, 2011). The prepared agarose gels, after sample loading, were submerged in a tampon with pH 8, knowing that DNA molecules have negative charge in mediums with a pH higher than 5, and that therefore they will migrate to the positive pole (Lima Pastrana, 2011). Each gel contained a concentration of 0,7% in agarose and was prepared mixing 0.35 grams of agarose with 50 ml of 100X Tris-Acetate-EDTA (TAE) buffer. To dissolve the agarose in the buffer, short periods of microwaving were necessary (around 30 seconds). After dissolving, the solution was poured in the electrophoresis tray, already prepared with the wells comb. It takes about 30 minutes to cool down, then, the comb is removed and the gel tray is ready to be introduced in the electrophoresis bucket. The bucket was filled with 100 X TAE buffer covering the wells before the samples were pipetted, avoiding so the removal of the samples from the wells.

Each sample had a volume of 20 µl, consisting of 16 µl autoclaved MilliQ H2O, 1 µl of DNA sample (the one obtained after the DNA extraction) and 3 µl of a loading buffer, to make the mixture heavier enabling the samples migration to the positive pole in the gel. A molecular weight ladder containing fragments of DNA with a known number of 9

base pairs (bp) and known concentration was included for the interpretations of the results. After closing the bucket, the electrical current was turned on for two hours at 70 mV. GelGreen™, a safer alternative to Ethidium Bromide and SYBR dyes was used to stain the gel dissolving 30 µl of the staining solution in 100 ml of MilliQ H2O in a bucket. One hour after the submergence of the gel in the staining solution, its content was revealed in a UV light lamp.

2.3.2. Polymerase chain reaction (PCR), amplification of ITS regions

Polymerase chain reaction, also known as PCR, is a method consisting on the exponential amplification through a three-step cycling process (Schochetman, et al., 1988) of a nucleic acid, or nucleotide sequences, in vitro. When amplifying a sequence, the ends must be known in sufficient detail to synthesize oligonucleotides that can hybridize it and initiate the reaction (Mullis & Faloona, 1987). Two synthetic oligos are necessary to work as primers, annealing at either end of the targeted nucleotide sequence to amplify in opposite directions orientation. After a proper annealing of the primers, the functioning of a DNA polymerase in multiple rounds of denaturation (opening the double helix), annealing and 3’ extension leads to an exponential amplification of the target sequence (Ho, Hunt, Horton, Pullen, & Pease, 1989). Primers ITS5 and ITS4 were used and their corresponding sequences are: ITS 5: GGAAGTAAAAGTCGTAACAAGG, ITS 5: GGAAGTAAAAGTCGTAACAAGG (White et al., 1990).

2.3.2.1. Reagents Polymerase chain reactions were carried out using the Platinum™ Taq Green Hot Start DNA Polymerase (Invitrogen™) with several modifications in the manufacturer specifications (Perkin Elmer Cetus). 100 µl of PCR reaction sample were prepared for each strain as follows: first, a master mix was prepared with 12.5 µl of 10 X Green PCR buffer, which contains among other substances Tris, that regulates the reaction pH, affecting the activity and fidelity of the enzyme and KCl, which increments the enzyme activity (Johnson, 2000; Schochetman et al., 1988), 2.5 µl MgCl2, 2.5 µl of 10 mM dNTP mix (dNTPs need Mg2+ to bind) and 0.5 µl of Platinum™ Taq DNA Polymerase. An insufficient amount of Mg2+ affects the DNA polymerase by stopping its reaction while its excess causes non-specific reactions (Johnson, 2000). Afterwards, 2.5 µl of both ITS5 and ITS4 primers were added in a concentration of 10 mM (they were firstly 10

diluted from 100 mM), mixed together with the master mix ,72 µl of autoclaved and filter sterilized MilliQ H20 and 5 µl of the DNA sample previously prepared in the DNA extraction. The 100 µl were divided in two small autoclaved Eppendorf tubes, having so each strain two PCR products.

2.3.2.2. Generation of PCR products 50 µl PCR samples were introduced in a thermal cycler to incubate the reactions. Even though the company had specifications, modifications on the times and temperatures of the cycles were necessary for the circumstances of the modified mixture. The thermal cycler was programmed for 35 cycles. First an initial denaturation at 94 ºC for 5 minutes was necessary, then, in each cycle a denature stage occurred at 94 ºC for 1 minute (due to de length of the sequence aimed to be replicated, this is, around 700bp), after, the anneal phase was carried out at 61.5 ºC (being this the optimal temperature for the primers to operate) for 30 secs and the extension stage took place at 72º for 50 seconds. Finally, the sample was hold at 4º indefinitely.

2.3.3. PCR product classification

Agarose gel electrophoresis can clear up the size (in bp) of the ITS fragments obtained in the PCR, determining if the PCR has been successful and has replicated the target fragment of the DNA molecule. The size of the bands belonging to the PCR samples can be defined by the proportional relation of the mobility of the sample in the gel and the empirical logarithm of its size (Lehrach et al., 1977). A ladder with standards of concentration and fragments size was necessary to set a calibration line in which the band migration of each strain PCR ITS fragment was extrapolated, thus, determining the fragment size. In this experiment, the ladder used was ZR 100 bp DNA Marker™ aiming to find the same or very similar fragment sizes in the PRC products as the PCR is expected to replicate the same sequence considered to length between 600-700 bp (White et al., 1990).

2.3.4. Purification of the PCR product gel bands

When the PCR product was considered to have the appropriate concentration, the next step was to purify the bands in the gel containing our target sequence, cleaning possible remaining PCR components. GenElute™ Gel Extraction Kit was the kit used and the fragment of interest was extracted from the agarose gel in a slice, deposited inside an

Eppendorf tube containing a silica binding column and dissolved and cleaned with products from the kit through several centrifugations. Our target, the ITS fragment, was expected to get stuck in the silica binding column and it only be released in the last step of the protocol, when releasing the clean sequence from the silica column.

2.3.5. Verification of an adequate amount of DNA in the samples

Before shipping the samples to the sequencing firm, it was important to know approximately the concentration of the eluted samples to fulfil the sequencing company requirements. To the achievement of this task, new agarose gels were prepared and several measurements were made in photographs taken from these gels to estimate the concentration of the ITS region in the purified tubes. In the photographs, the luminance of the bands was measured. To estimate the concentration of a band, a luminance value is given to the molecular weight markers with known concentration, 600 bp, 26 ng and 700 pb, 24 ng. An average of both luminance and concentration values of the two ladder bands was used to calculate the concentration of the sample bands because the expected ITS regions were expected to appear between 600 bp and 700 bp. The calculation procedure was a simple proportion of luminance-concentration. For making a more accurate experiment, each luminance value was an average of 3 luminance values measured along the gel band.

2.3.6. Preparation of sequencing samples

After measuring the concentrations of the purified ITS region, the samples were prepared to be sent to LIGHTRUN tube, a sequencing PCR fragments company which uses Sanger light-speed methodology. The sample requirements were related to the concentration of the DNA template, between 20 ng and 80 ng, and its amount, minimum 5 µl, as well as the primer’s amount and concentration, 5 µl in concentrations of 5 µM for each primer, ITS4 and ITS5.

2.3.7. Sequencing

Sequencing samples arrived three working days after the shipping. They came with the analysed sequence in three different kind of files: .seq (the sequence), .ab1 (the electropherogram) and .fas (for a FASTA DNA-program).

2.3.8. Identification

The sequences were analysed and edited by using the package DNAStar®, making alignments and visually correcting the sequences by using the software MegAlign™. For the identification, the obtained sequences were compared with those known of all yeast species available at the GenBank database of the US National Centre for Biotechnology Information (NCBI). For this task, the Basic Local Alignment Search Tool (BLAST) available at http:// www.ncbi.nlm.nih.gov was used.

2.4. Vanillin resistance experiments Several Sporidiobolales strains were tested in diverse minimum medium to study their reaction to different concentrations of vanillin. The growth of a strain in a medium with a higher concentration of this phenolic compound would make the strain to be considered as good degrader of vanillin and therefore, object of study in liquid culture experiments, studying its capacity for biodegrading vanillin aiming to understand a bit better its biodegradation pathway.

2.4.1. Selection test of the most resistant isolates

In a first screening experiment, the 39 isolates were tested together with an isolate belonging to another yeast collection, FMYD002 (Nehvonen, C., 2017) already used for some vanillin tests. A total of 40 strains were imprinted and transferred from YEPD- agar petri dishes to several LiBa-agar petri dishes (20 colonies per plate) with different concentrations with replica prong. The experiment had two variants, one consisted on transferring the colonies grown for 48h in YEPD-agar plates to LiBa-agar plates with concentrations of LiBa-VA 0 mM, LiBa-VA 1 mM , LiBa-VA 5 mM and LiBa-VA 10 mM all at the same time. The second variant of this experiment, consists on the transference of the colonies in order of increasing concentration from one plate to another only after their growth was evident. Thus, the not vanillin resistant strains were ruled out leading to the permanence of the best candidates withstanding high concentrations of vanillin.

2.4.1.1. Solid culture media preparation

LiBa-agar plates are prepared mixing a stock of LiBa with autoclaved MilliQ H2O containing agar up to a 2 %. Different amounts of vanillin stock solution (0.1 M) were added to the flask containing LiBa-agar after pouring the plates. The flask contained 320 ml and each plate 20 ml of the medium, starting from LiBa-agar, and continuing in 13

crescent concentrations of vanillin order (1 mM, 5 mM and 10 mM). From each concentration four plates were prepared making a total of sixteen plates. Single colonies of the strains were cultivated with toothpicks in regular YEPD-agar plates following the pattern of the replica prong to make the transference easier.

2.4.2. Vanillin resistance and degradation in liquid cultures

The strains that showed more resistance in the solid cultures were selected to grow in the same vanillin concentrations (0 mM, 1 mM, 5 mM and 10 mM) in liquid LiBa cultures, extracting samples in certain timepoints.

2.4.2.1. Experiment setup Before starting the proper experiment, a preculture to set the concentration of the main experiment was necessary. A loopful of the selected strain was grown in 40 ml of liquid LiBa for 24 h. Afterwards, the number of cells was measured and each flask of the experiment set at a concentration of 6 x 106 CFU/ml. The experiment consisted of eight flasks, four flasks containing 60 ml of LiBa and concentrations of 0 mM, 1 mM, 5 mM and 10 mM of vanillin and a cell concentration of 6 x 106 CFU/ml of the selected yeast strain taken from the preculture, and other four containing the same concentrations of vanillin but without the yeast, this is, controls. The flasks stayed 192 hours in a circular shaker at 230 rpm and 25 ºC (in a sterile environment) and six timepoints were established at 0, 12, 24, 36, 48 and 196 h to collect samples aiming to see how the yeast degrade the supplemented vanillin in each medium.

2.4.2.2. Sample collection At each timepoint, two millilitres of each flask were extracted and transferred to Eppendorf tubes, spin at 4000rpm for 5 minutes and filter sterilized with a syringe. Each sample was kept in the freezer at -20 ºC and defrosted to prepare a thin layer chromatography

2.4.2.3. Thin layer chromatography (TLC) Thin layer chromatography is a separation technique used in qualitative analysis of compounds. TLC enables to monitor the progress of a reaction, the number of components in a mixture, and it also gives an idea of the sample’s purity (Hess, 2007). This technique has two phases, a stationary phase consisting on a silica slab coated on aluminium and a glass chamber in which the back of the slab lays, and a mobile phase, the eluent, made of a mixture of toluene, ethyl acetate and formic acid (4:5:1). Capillarity is the principle of this methodology allowing the migration of the eluent and 14

the compounds upwards in the silica slab (Hahn-Deinstrop, 2007). Each compound has a different affinity and polarity which affects the migration speed and the separation of the compounds. Less polar compounds migrate further upwards while polar compounds stick the polar silica slab, reducing the migrating speed. Usually TLC experiments take 80 min and the elution must be stopped before reaching the top of the silica slab. After, the TLC can be studied under UV light or MBTH staining.

2.4.2.3.1. Sample preparation Each sample for the TLC was taken from the frozen samples that were collected from the main culture flasks. The samples were transferred to glass tubes and adjusted to pH 2 with HCl 1 M. For 2 ml, 800 µl of ethyl acetate were added dividing the mixture in two phases, an organic phase constituted by the ethyl acetate and an inorganic phase consisting of the LiBa medium. The samples were centrifuged for 5 min at 5000 rpm and during the spin the compounds stick to the ethyl acetate. 500 µl of the organic phase were extracted, transferred to small glass tubes, and dried with gaseous N2 (this step takes around 15 min). Once the samples dried, 20 µl of ethyl acetate were added to the tube resuspending the compounds. The 20 µl samples and 10 μl standards of vanillin 10 X (5 mM), vanillyl alcohol 10 X (5 mM) and vanillic acid 5 X (10 mM) were pippeted in the silica slab in small doses, using a hair dryer to dry each drop before adding the next. After the TLC plate was introduced in the chamber with the eluent. The standards were chosen to help identifying the vanillin degradation sub-products providing guidance in the staining contrast and travel distance of the stationary phases on the TLC plates.

2.4.2.3.2. Treatment of the data When revealed, the chromatography showed the compounds at different heights, this migration distance is a signature of every compound found in the sample (Hahn- Deinstrop, 2007). The data were treated using the retention factor (Rf) values of each sub-product, consisting on the distance travelled by the sample over the distance travelled by the eluent (solvent front). 2.5. Yeast growth in vanillin supplemented medium The isolates were expected to struggle growing as the vanillin concentration increases due to the known fact that vanillin is an inhibitor in yeasts growth at small concentrations (Endo et al., 2008).

2.5.1. Cell count in Neubauer’s chamber

Haemocytometers enable cells counting. Neubauer’s chamber consist of a thick crystal plaque divided in three sections. In the central section, a quadrangular grid is engraved containing two counting areas, each of them divided in nine squares of 1 mm square each. To prepare the samples, 20µl of each flask were extracted at the same timepoints as the TLC samples, diluted in 180µl of LiBa, and 10 µl were added to 10 µl of methylene blue. 10 µl of each sample were pippeted in the chamber, covered with a glass slide and observed at 40x in the microscope. Neubauer’s chamber formula is: 푐푒푙푙푠 푛푢푚푏푒푟 푥 10000 푐푒푙푙 푐표푛푐푒푛푡푟푎푡푖표푛 = (푛푢푚푏푒푟 표푓 푠푞푢푎푟푒푠 푥 푑푖푙푢푡푖표푛) Where “10000” is the area of each big square: • 0,1cm x 0,1cm = 0,01cm2 (area of a square) • 0,01cm2 x 0,01cm (depth) = 0,0001cm3

Neubauer’s chamber is also used to measure the cell concentration from the preculture.

3. Results 3.1. Identification experiments The main aim was to optimize and find out the correct proportions of chemicals in the different steps of the identification of yeast strains. The experiments were successful and can be replicated.

3.1.1. DNA extraction

A first attempt of DNA extraction was done, unfortunately, with an outdated phenol. In a second try all the samples succeeded in the DNA extraction. Nevertheless, the samples were not as clean as aimed, therefore an RNAse treatment was included in the protocol. Due to the immense size of DNA molecules, the samples did not migrate much down in the gel. All in all, the gels showed a successful DNA extraction, and therefore the experiments of DNA fingerprinting were carried out.

3.1.2. PCR product

After all the cycles in the thermal cycler were completed, the PCR product was checked through an agarose gel. The gel results proved the PCR to be successful. An analysis of the band sizes and migrations was performed to assure that all the ITS fragments

replicated in the PCR had a similar base pairs (bp) amount, this is, that all the fragments have an approximate size (Table2-3).

Table 2-3: sizes of PCR products and migration distance after amplification of genomic DNA with primers ITS4 and ITS5. A) Strains of the culture collection strain L2 L4 L105 L151 L153 L154 L155 L156 L160 L166A L177 L200

Migration (mm) 30 30 30 30 29 29 30 29 29 29 30 30

Fragments size (bp) 625 625 625 625 675 675 625 675 675 675 625 625

L206 L209 L215 L234 L241 L384 L388 L389 “E.hasegawianum” L393

30 30 30 29 31 30 30 30 30 31

625 625 625 675 600 625 625 625 625 600

L212 L400 L411 L249 L257 L268 L269 L359 L386 “Rhodotorula sp.” L452 L394

30 30 30 30 30 30 31 30 31 31 30 30

625 625 625 625 625 625 600 625 600 600 625 625

B) Reference strains strain LS11 L-76-2 LS22 LS28 “Sporobolomyces sp.

Migration (mm) 30 30 31 33 24

Fragments size (bp) 625 625 600 500 1000

Ladder fragments size (bp) 19 22 24 25 26 28 31 33 35 38

Migration (mm) 1500 1200 1000 900 800 700 600 500 400 300

PCR product analysis 1050 34 950 32 850 30 28 750 26 650 24

550 22 (mm) Migration

450 … 20

Fragments size (bp) Fragments

L2 L4

L156 L269 L105 L151 L153 L154 L155 L160 L177 L200 L206 L209 L215 L234 L241 L384 L388 L389 L212 L400 L411 L249 L257 L268 L359 L386 L393 L394 L452

LS22 LS28 LS11

L-76-2

L166A

“S. Roseus” “S.

“Erytrhobasidiu “Rhodotorula sp.” “Rhodotorula

Fragments size (bp) Migration (mm)

Figure 1: PCR product: analysis of the proportional relation between the sample migration through the gel and the size of the fragments. 17

The analysis of the band sizes and band migration (Figure 1, Table 2-3), showed that all the culture collection strains have ITS fragments of the expected amount of bp (600- 800bp).

3.1.3. Gel elution and recovery of purified ITS fragments

After the purification and elution of the ITS regions extracted from gel slices, the concentration of the template DNA vas determined through luminance measurements of the bands to fulfil the requirements (20-80 ng/µl) of the sequencing company (LightRun). Due to a lack of time, not all the samples reached this stage in the path to sequencing.

3.1.4. Verification of required minimum concentration of template DNA

The ITS regions of strains L4 and L105 showed the highest concentration in PCR product and therefore were selected to be shipped to the sequence company. During the gel elution process, DNA losses could reach a 50%, so the concentration of the samples was checked after the elution. Three luminance measurements were made for each band and an average value (Table 4) was be used to relate luminance with concentration.

Table 4: Luminance values (Nits) average of the template DNA measured in gels run after the gel elution Luminance measures 1st 2nd 3rd Average L4 155 155 155 155 L105 155 156 155 155,33 L151 112 113 112 112,33 Ladder 700 146 145 146 145,67 Ladder 600 145 145 145 145 Table 5: Luminance-concentration relation. The concentration of the fixed average ladder was 25 ng/µl and the luminance 145,33 Nits and the results come from the direct proportion existing between luminance and onncentration. Strains and ladders Luminance (Nits) Concentration (ng/µl) L4 155 26,66 L105 155,3333333 26,72 L151 112,33 19,32 600-700 ladder 145,33 25 Luminance and concentration are directly proportional values (Table 5). The estimated value for the samples was higher than the minimum required and therefore the samples were prepared and sent to the company.

3.1.5. Identification results

Positive sequencing results were obtained from the company for both strains. Among the diverse results found in a preliminary analysis it was possible to confirm that both strains belong to the species Rhodotorula babjevae as their closest match was the strain 18

CBS-322 in the CBS culture collection, designated as Rhodotorula babjevae (Vu et al., 2016). 3.2. Vanillin experiment: selection of most vanillin resistant isolates As shown in Figure 2, in the experiment in which the strains were transferred with a replica prong from YEPD plates simultaneously to the different concentrations of LiBa- VA and grown for 48 hours, all the strains show growth in LiBa and LiBa-VA 1 mM plates, while no growth is noticed in the LiBa-VA 5 mM and LiBa-VA10 mM plates.

The gradual transference experiment showed more hopeful results (Figure 2) as in LiBa-VA 5 mM plates, after many hours, Rhodotorula babjevae (strain L4) and Rhodosporidium kratochvilovae (strain LS22) grew. In LiBa 10 mM, only strain L4 grew. The two strains, due to their capacity to withstand higher concentrations of vanillin were chosen to be studied in liquid LiBa-VA experiments, the biodegradation pathway of vanillin and how the strains growth was affected in its different concentrations. 48 h cultures Growth after gradual transfer to increasing concentrations of vanillin (VA) A 7 days growth

B B 5 days growth

C 10 days growth

5 days growth

10 days growth

D 16 days growth

Figure 2: growth of red yeasts on Lilly Barnet (LiBa) medium supplemented with: (A) LiBa without VA; (B) LiBa + 1 mM VA; LiBa + 5 mM VA; and (D) LiBa + 10 mM VA. The plates in the left column refer to a simultaneous transference of the yeasts grown in YEPD for 24 hours directly to all the plates with the different concentrations and grown for 48 h. In the right column, the colonies were only transferred to an increasing concentration after they grew in the plate. Numbers in the plates refer to the strain names (see Table 1).

3.3. Vanillin biodegradation in liquid cultures, TLC results Vanillin biodegradation was studied through TLC plates running each strain samples collected at 0, 12, 24, 36, 48 and 192 hours from the 4 different flasks containing the liquid cultures with LiBa, LiBa-VA 1 mM, LiBa-VA 5 mM and LiBa-VA 10 mM and the Rf of the revealed compounds was measured (Table 6), finding eight different intermediaries in this cultivation process.

Table 6: Compounds revealed in TLC plates and their corresponding Rf value for Rhodotorula babjevae and Rhodosporidium kratochvilovae.. Vanillin Comp. Y Comp. A Comp. X Comp. B Comp. C Comp. D Comp. E Rf 0,8 0,74 0,67 0,65 0,64 0,62 0,58 0,49 For both, Rhodotorula babjevae and Rhodosporidium kratochvilovae the TLC results showed degradation products of LiBa medium which were obviated (compounds A, B, C, D and E). Rhodotorula babjevae, (Figure 3) at concentrations of LiBa-VA 1 mM showed the consumption of all the vanillin by the yeast in the first 12 hours. At time 0 had already started degrading vanillin in compound X, which has the same Rf value as the standard of vanillyl alcohol used. Once the vanillin disappeared the remaining compounds, compound X and compound Y (with a Rf value similar to the one obtained in the vanillic acid standard), were stable until 48 hours, and after 192 hours only compound X remained. At concentrations of vanillin 5 mM, and 10 mM vanillin and compound X were present during the 192 hours, in LiBa-VA 5 mM, compound Y appeared at 48 hours and remained even after 192 hours while in LiBa-VA 10 mM, compound X appeared at 48 hours and at 192 hours it was already gone.

Rhodotorula babjevae: vanillin biodegradation products 1 0,8 0,6 Rf Rf 0,4 0,2

24 LiBa 1 mM 1 LiBa 24

192 LiBa-VA 10 LiBa-VA 192

0 LiBa-VA 1 mM 1 LiBa-VA 0 mM 5 LiBa-VA 0

12 LiBa-VA 1 mM 1 LiBa-VA 12 mM 1 LiBa-VA 36 mM 1 LiBa-VA 48 mM 5 LiBa-VA 12 mM 5 LiBa-VA 24 mM 5 LiBa-VA 36 mM 5 LiBa-VA 48 10 mM LiBa-VA 0

192 LiBa-VA 1 mM 1 LiBa-VA 192 mM 5 LiBa-VA 192 mM 10 LiBa-VA 12 mM 10 LiBa-VA 24 mM 10 LiBa-VA 36 mM 10 LiBa-VA 48 Time (h)

Vanillin Compound Y Compound X

Figure 3: Biodegradation products of vanillin by Rhodotorula babjevae in LiBa, LiBa-VA 1 mM, LiBa-VA 5 mM and LiBa-VA 10 mM In the TLC results for strain Rhodosporidium kratochvilovae, Figure 4, it was assumed that at concentrations of vanillin 1 mM, all the medium was consumed by the yeast during the first 24 hours due to the lack of products after 36 hours. At time 0, only vanillin appeared and after 12 hours it had already been transformed in compound Y and compound X, which disappeared after 24 hours. At concentrations of vanillin 5 mM, and 10 mM, vanillin stayed during the 192 hours, compound X disappeared after 192 hours and compound Y, formed at 36 hours, remained until the end of the experiment in vanillin 5 mM flask while in vanillin 10 mM it was already consumed at 192 hours.

Rhodosporidium kratochvilovae: vanillin biodegradation products 1 0,8 0,6

Rf 0,4 0,2

24 LiBa 1 mM 1 LiBa 24

192 LiBa-VA 10 LiBa-VA 192

0 LiBa-VA 1 mM 1 LiBa-VA 0 mM 5 LiBa-VA 0

24 LiBa-VA 5 mM 5 LiBa-VA 24 12 LiBa-VA 1 mM 1 LiBa-VA 12 mM 1 LiBa-VA 36 mM 1 LiBa-VA 48 mM 5 LiBa-VA 12 mM 5 LiBa-VA 36 mM 5 LiBa-VA 48 10 mM LiBa-VA 0

48 LiBa-VA 10 mM 10 LiBa-VA 48 192 LiBa-VA 1 mM 1 LiBa-VA 192 mM 5 LiBa-VA 192 mM 10 LiBa-VA 12 mM 10 LiBa-VA 24 mM 10 LiBa-VA 36 Time (h)

Vanillin Compound Y Compound X

Figure 4: Biodegradation products of vanillin by Rhodosporidium kratochvilovae in LiBa, LiBa-VA 1 mM, LiBa-VA 5 mM and LiBa-VA 10 mM

3.4. Vanillin resistance: Neubauer’s chamber results

To measure the resistance of the yeast to different concentrations of vanillin, the cell growth was measured in six timepoints (0, 12, 24, 36, 48 and 192 hours).

Growth of Rhodotorula babjevae in different VA concentrations

LiBa LiBa-Va 1 mM LiBa-VA 5 mM LiBa-VA 10 mM

40 scale)

6 30 20 10 0

CFU/ml 10CFU/ml x (in 0 12 24 36 48 192 Time (h)

Figure 5: growth of Rhodotorula babjevae in cultures with different concentrations of VA for 192 hours As shown in Figure 5, Rhodotorula babjevae showed a better average growth in a LiBa medium supplemented with 1 mM vanillin than it did in LiBa. This indicates that probably small doses of vanillin can nutritive for the strain, enhancing its growth. Even though, at 36 hours the growth was excellent, afterwards it started to decrease until 192 hours (unlike in LiBa medium in which the strain kept growing at 192 hours). In the beginning the strain seemed to struggle to grow in the medium until it could benefit from it. In concentrations of vanillin 5 mM the growth was very poor and after 48 hours the cells started their apoptosis and in concentrations of vanillin 10 mM the strain didn’t grow until 36 hours and after it died.

Growth of Rhodosporidium kratochvilovae in different VA concentrations

LiBa LiBa-Va 1 mM LiBa-VA 5 mM LiBa-VA 10 mM

70 60

scale) 50 6 40 30 20 10 0 CFU/ml 10 x (in CFU/ml 0 12 24 36 48 192 Time (h)

Figure 6: growth of Rhodosporidium kratochvilovae in cultures with different concentrations of VA for 192 hours Rhodosporidium kratochvilovae showed different results in its growth (Figure 6). In LiBa medium, the strain grew until 36 hours and after that the cells concentration

started to decrease unlike it happened with Rhodotorula babjevae. In vanillin 1 mM supplemented medium the strain reached its peak of growth after 2 hours and after that it seemed like it had consumed all the medium due to its vast decrease in cell concentration. At concentrations of vanillin 5 and 10 mM the strain progressively reduces the number of cells, as it happens with strain L4.

4. Conclusions and discussion

The results obtained in the identification study show that the performed and optimized experiments work for obtaining a clean ITS sequence, this means that the rest of the strains which were selected for these experiments and that have not been identified yet, can be identified reproducing these experiments. The fact that the two identified strains belong to the same species (Rhodotorula babjevae) and one withstands high concentrations of vanillin while the other one does not opens a question mark for the rest of the strains, does the location of collection of the sample has an influence in the species variation regarding vanillin biodegradation? It seems like a possibility as strain LS11, Rhodosporidium kratochvilovae, a good biodegrador of patulin (Castoria et al., 2005) is not resistant to vanillin, while, LS22, also Rhodosporidium kratochvilovae, sampled from potatos does biodegrade vanillin. This opens a second question mark, does the resistance to vanillin can be a consequence of the usage of herbicides? Also, morphological studies can take place to find out if a genomic identification would match with a morphological characterization distribution of the isolates. The strain Rhodosporidium dibovatum has been studied and documented as capable of growing in the presence of vanillin (Luque et al., 2016) also, it was one of the strains with the most similar ITS region to the one in Rhodotorula babjevae when the sequence was introduced in the NCBI database. A futher study could consist on a classification of ITS regions similarity and the capacity of the microorganisms withstandig vanillin. Even though, exceptions were found such as the disparity between the ITS region length found in Sprobolomyces sp. and L-76-2 which belong to the same species. It could be due to inespecific amplifications during the PCR. It can be concluded that strains L4, Rhodotorula babjevae, and LS22, Rhodosporidium kratochvilovae were the two best strains growing in LiBa medium supplemented with increasing concentrations of vanillin. Strain L4 in liquid cultures of LiBa-VA 1 mM, consumed the medium more slowly than strain LS22, and that all in all, both of them 23

soon or later produce the same biodegradation products from vanillin, with Rf values similar to the ones for vanillic acid and vanillyl alcohol. It is also remarkable the influence of small doses of vanillin in the growth of yeasts, concretely in strain LS22 once the vanillin is already degraded (1 mM VA) not only the subproducts are consumed, what is more, if the results of Figure 6 are contrasted to the results in Figure 4, it is possible to appreciate that the time in which the cells start to die correspond to the time in which the biodegradation products are consumed. Studies performed with strain FMYD002 (Nehvonen, C., 2017) also showed better growth patterns supplementing the medium with 1 mM VA than only growing the yeast with LiBa. 5. References

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