Fadahunsi et al. Bull Natl Res Cent (2020) 44:185 https://doi.org/10.1186/s42269-020-00436-3 Bulletin of the National Research Centre RESEARCH Open Access Efect of cultural conditions on the growth and linamarase production by a local species of Lactobacillus fermentum isolated from cassava efuent Ilesanmi Festus Fadahunsi1* , Nafsat Kemi Busari1 and Olumide Samuel Fadahunsi2,3 Abstract Background: This study was designed to investigate the efect of cultural conditions on growth and production of linamarase by a local species of Lactobacillus fermentum isolated from cassava efuent. Isolation and identifcation of bacteria from cassava efuent were carried out using the culture-dependent method and polyphasic taxonomy, respectively, while screening for cyanide degradation, and the efects of cultural conditions on the growth and lin- amarase activity of L. fermentum were investigated based on standard procedures. Results: A total of twenty-one bacterial isolates were obtained from cassava efuent, and isolate MA 9 had the highest growth of 2.8 1010 cfu/ml in minimum medium, confrmed as safe, identifed as Lactobacillus fermentum and selected for further× study. The highest growth of 2.498 OD and linamarase activity of 2.49 U/ml were observed at inoculums volume of 0.10 ml at 48-h incubation period, while optimum growth of 1.926 OD and linamarase activity of 1.66 U/ml occurred at pH 5.5. At 37 °C, the optimum growth of 0.34 OD was recorded with the highest linamarase activity of 0.81 U/ml at 30 °C.However, the incubation period of 48 h stimulated an optimum growth of 3.091 OD with corresponding linamarase activity of 1.81 U/ml, while the substrate concentration of 400 ppm favours a maximum growth of 2.783 OD with linamarase activity of 1.86 U/ml at 48 h of incubation. The supplemented of 10 mM calcium ions stimulated optimum linamarase activity of 2.65 U/ml. Conclusion: Lactobacillus fermentum could be used as starter culture in cassava fermentation for the production cassava-based product with reduced cyanide content. Keywords: Cultural conditions, Production, Linamarase activity, Lactobacillus fermentum, Cassava efuent Background β-D-glucopyranose and acetone cyanohydrin which Linamarase (EC 3.2.1.21) along with its naturally occur- are further degraded to acetone and hydrogen cyanide ring substrates, linamarin and lotaustralin, is found in a (HCN), respectively (Nartey 1968; Cooke 1978; Rolle variety of edible plants such as cassava, lima beans and 1998; Murugan et al. 2012; Nwokoro 2016). In the pro- fax. It is a well-studied hydrolytic enzyme that has also duction of garri (a household West African food material been isolated from members of eukaryotes, bacteria, four), the enzyme plays an important role in the batch- fungi and archaea. It hydrolyses linamarin to produce wise detoxifcation process of cassava fermentation and degradation of cyanogenic compounds to produce HCN which either dissolves readily in water or released into *Correspondence: [email protected] the air in a process known as cyanogenesis (Ikediobi 1 Department of Microbiology, Faculty of Science, University of Ibadan, Ibadan, Oyo State, Nigeria and Onyike 1982; Kostinek et al. 2006). Microorgan- Full list of author information is available at the end of the article isms have also been documented to exhibit the ability to © The Author(s) 2020. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creat iveco mmons .org/licen ses/by/4.0/. Fadahunsi et al. Bull Natl Res Cent (2020) 44:185 Page 2 of 14 disintegrate cyanide-containing compounds into acetone agar (NA) were poured one after the other into the Petri cyanohydrins by producing linamarase (Nwokoro 2016). dishes (Harrigan and McCance 1966). Te MRS plates In addition, some phytopathogenic fungi like Fusarium were incubated at 37 °C for 24 h in an anaerobic jar, solani are capable of degrading cyanide. However, bio- while nutrient agar plates were incubated aerobically. degradation by bacteria is preferable because it shows Discrete colonies that grew on the plates were counted considerable advantage since bacteria are more eas- and recorded as colony-forming unit per millilitre (cfu/ ily manipulated both at biochemical and at genetic lev- ml). Representative colonies were selected and streaked els (Okafor and Ejiofor 1985; Huertas et al. 2006; Abban repeatedly to obtain pure isolates which were maintained et al. 2013; Ahaotu et al. 2013). Cyanide is a toxic chemi- on MRS and nutrient agar slants in refrigerator for subse- cal compound present in plants seeds, bitter almonds, quent use. apricots, peaches and inorganic salts such as sodium and potassium cyanides. In cassava tubers, cyanide is avail- Screening for linamarase‑producing bacteria able in the form of cyanogenic glucosides, linamarin Screening for linamarase-producing bacteria was carried and lotaustralin which are major safety concerns among out by inoculating diferently a single pure colony of the cassava consumers and processor (Dunstan et al. 1996). bacteria isolated from cassava efuent into 10 ml sterile Cyanide is a widely known inhibitor of cellular energy MRS and nutrient broth in diferent test tubes. Incuba- generation that occurs during oxidative phosphoryla- tion was done anaerobically at 37 °C for 48 h in an anaer- tion. It binds to a large enzyme of the inner mitochon- obic jar to generate a growing and activated inoculum drial membrane (cytochrome oxidase), thus preventing suspension, while that of nutrient broth was done aero- the transfer of electrons to molecular oxygen and gen- bically. One millilitre of the activated cells suspension eration of adenosine triphosphate (ATP) (Nelson and was transferred diferently into 100 ml of sterile MRS Cox 2005; Tefera et al. 2014). Intake of 50 to 100 mg of and nutrient broth containing 100 ppm of flter-sterilized cyanide has been observed to elicit poisoning which is potassium cyanide (KCN) as the sole nitrogen source in fatal to humans, while long-time consumption of trace a 250-ml Erlenmeyer fask placed on rotatory shaker for amounts has been implicated in the aetiology of tropical 48 h at 37 °C. One millilitre of the agitated suspension neuropathy, fbrocalculous pancreatic diabetes (FCPD), was pipetted and serially diluted to 10–8 dilution, and 1 glucose intolerance coupled with iodine defciency goi- ml was taken and diferently plated on sterile MRS and tre and cretinism (Mathangi et al. 2000; Cardoso et al. nutrient agar plates. Te MRS was incubated anaerobi- 2005). Hitherto, it had been reported that most locally cally at 37 °C for 48 h in an anaerobic jar, while the nutri- produced cassava-based products contain cyanide higher ent media was incubated aerobically at the same time and than the World Health Organization (WHO)-recom- temperature. Plates were examined for bacterial growth, mended safety level (Owuamanam et al. 2010). In this and the observed colonies were counted physically to context, this research is aimed at investigating the efect measure the growth/survival in cyanide environment. of cultural conditions on the growth and linamarase pro- Representative colonies were selected and subcultured duction by a local species of Lactobacillus fermentum severally to obtain pure colonies which were stored on isolated from cassava efuent. agar slants in McCartney bottles and kept in the refrig- erator. Te isolate with the highest growth was selected Methods for further studies. Sample collection Cassava efuent was collected from diferent cassava pro- Safety assessment test for bacteria cessing plants around Agbowo axis in Ibadan, Oyo State, Gelatinase test at 10:00am on 26 September 2019. Te samples were col- Gelatinase activity was investigated as described by lected aseptically in clean sterile bottles and transported Harrigan and McCance (1966). A 24-h-old culture was to the Food Biotechnology Postgraduate laboratory, streaked on nutrient gelatin agar and inoculated anaero- Department of Microbiology, University of Ibadan, Nige- bically for 48 h at 37 °C and fooded with HgCl2 solutions ria, for immediate isolation of bacteria. (15% HgCl2 in 20% HCl, v/v). Clear zones surrounding colonies were noted for positive reaction indicating gela- Isolation of bacteria from cassava efuent tin hydrolysis. Te sample was serially diluted by transferring 10 ml of cassava efuent into 90 ml of sterile distilled water, and DNase test 1 ml from 104 dilution test tube was transferred into Te isolate was tested for the ability to produce deoxyri- sterilized Petri dishes. Sterile 20 mls of De Man, Rogosa bonuclease. Tis was carried out by streaking the isolate and Sharpe agar (MRS agar) with pH 5.5 and nutrient on DNase agar and incubated for 24 h, and the plate was Fadahunsi et al. Bull Natl Res Cent (2020) 44:185 Page 3 of 14 fooded with concentrated HCl (Harrigan and McCance 1966). Haemolytic activity Haemolytic test was carried out with nutrient agar sup- plemented with 5% sheep blood. Te plates were inocu- lated aseptically and incubated for 48 h at 37 °C and examined for greenish colouration halos to confrm the production of α-haemolysin which indicates partial hae- molysis, while complete clear zone indicated the produc- tion of β-haemolysin (Akinjogunla et al.