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Aerobic Conversion of Dimethyl Sulfide and Hydrogen Sulfide by Methylophaga Sulfidovorans: Implications for Modeling DMS Convers

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Aerobic Conversion of Dimethyl Sulfide and Hydrogen Sulfide by Methylophaga Sulfidovorans: Implications for Modeling DMS Convers MICR8810bOGY ECOLOGY ELSEVIER FEMS Microb~ologyEcology 22 (1997) 155-165 Aerobic conversion of dimethyl sulfide and hydrogen sulfide by Methylophaga sulfidovouans: implications for modeling DMS Downloaded from https://academic.oup.com/femsec/article/22/2/155/541232 by guest on 27 September 2021 conversion in a microbial mat Jolyri M.M. de Zwart *, J. Gijs Muenen Department of Microbiology and Enzymology, Deqt University of Technology, Julianalaan 67, 2628 BC Delft, The Netherlands Received I August 1996; revised 7 November 1996; accepted 8 November 1996 Abstract Methylophaga su~fidovorans is an obligately methylotrophic, DMS-oxidizing organism, isolated from microbial mat sediment. DM§ and H2S, both present in marine microbial mats, can be used as energy sources by this organism. In batch cultures of M. sulfidovorans, sequential H2S and DMS utilization occurred. In energy-limited continuous cultures, with DMS, methanol and H2S as substrates, mixotrophic growth of M. sulfidovorans was observed, showing that at low concentrations these substrates can be used simultaneously. Oxygen and H2S uptake experiments showed that the critical concentration at which sulfide inhibiticn of EMS oxidation occurred was between 15 and 40 p~!!-I. '*.!so ir, crude enrichmezts of D?dS oxidizers a decrease of 50% in DMS-oxidizing capacity for about 200 pmol l-' Hz§ was observed. The new physiological data obtained with the pure cultures of &I. ssu~idovoranswere incorporated in a compartment model of a microbial mat and gave improved predictions of DMS profiles and DMS emissions from the mat, both when phototrophic activity is present (day) and when it is absent (night). Keyrrjords: Microbial mat; Dimethyl sulfide oxidation; Hydrogen sulfide oxidation; Compartment rnodei; Methylophaga .sul$dovorans 1. Introduction convert organic sulfur compounds. The different groups of microorganisms produce and consume sev- In marine microbiai mats, different functional eral sulfur compounds, of which H2S and DMS are groups of microorganisms form a cooperative com- important representatives. H2S is often produced in munity [I]. The quantitatively most important func- large amounts by sulfate-reducing bacteria. h sul- tional groups are well-described, and consist of fate-reducing activity of 10 pmol ml-' day-' was phototrophs, colorless sulfur bacteria, heterotrophs measured in a Microcoleus chthonoplastes-dominated and sulfate-reducing bacteria. A quantitatively less microbial mat [2]. These high production rates may important group is the population of bacteria that result in sulfide concentrations as high as 200-500 ~mol1-' in the lower, anoxic layers of a mat [3]. HzS is oxidized to sulfate by the (aerobic) colorless -- * Corresponding author. Fax: +3S (IS) 278 2355; and (anoxygenic) phototrophic sulfur bacteria. The e-mail: [email protected] resulting concentration gradient leads to upward dif- 0168-6496197/517.00 Copyright C 1997 Federation of European Mic~.obiologicaSSocieties. Published by Eisevier Science B.V. PIIS01 68-6496(96)00086-4 156 J M. ;M. de Zbvnrt, J. 6. Kuenen l FEiMS Microbiology Ecology 22 11997; 155-165 fusion of H2S in the mat. DMS occurs in much were used as a validation for the assumption that smaller amounts than sulfide. In marine sediments, kinetic and physiological data of M. su&dovorans the main source of DMS is biological degradation of can be used in simulations during a diurnal cycle. dimethyl sulfoniopropionate (DMSP) 141, an osmo- lyte present in many phoiotrophs [5]. The production rate of DM§ during a bloom period of a marine 2. Materials and methods microbial mat was estimated to be + 20 nmol mi-' day-I (a factor 500 lower than sulfide production) 2.1. Bacterial culture and natural samples and coupled to photosynthesis [6]. DMS degradation in sedirncnts can take place under oxic and anoxic Microbial mat sediment samples were obtained in conditions [7-91. Since it is formed in the upper, May 1996 from the Oosterschelde, an estuarine inter- Downloaded from https://academic.oup.com/femsec/article/22/2/155/541232 by guest on 27 September 2021 genera!!y oxic, layer of the mat, it is ass~medthat tidal region on the south-west coast of the DMS will be converted primarily by aerobic bacter- Netherlands. Methylophaga suljidovorans (L,MD ia. As already found, H2S and DMS coexist near the 95.210) had been previously isolated from microbial oxic/anoxic interface of the mat [8]. H2S is consid- mat sediment samples obtained from the same site ered to be an intermediate in the aerobic DMS me- PI. tabolism of known DMS-oxidizing bacteria [9-131, and can be used as a supplementary energy source 2.2. Culture media for growth. Little is known, however, of possible diauxic or inhibitory effects when DMS and H2S Mineral medium contained per liter: 15 g NaCI, are supplied together, or whether the presence of 0.5 g (NH4)2S04, 0.33 g GaC12.6H20, 0.2 g KCI, 1 g H2S affects DMS degradation. These factors may MgS04.7H20, 0.02 g KHzP04, 2 g Na2C03, 1 mg have a considerable effect on the prediction of the FeS04-7H20,1 ml trace element solution [9j, 1 ml release of DM§ from a microbiai mat into the atmo- vitamin solution [9]. pH was maintained at 7.5 sphere. (20.3) with 1 N HC1. Liquid medium containing Using the highest dilution to extinction method, a DMS was kept in glass bottles, which were sealed specialist in aerobic DMS oxidation has been iso- with butyi rubber stoppers to prevent DMS loss. lated: Methylophaga sulJidovorans [9]. This bacterium The purity of the cultures was routinely checked is an obligate methylotroph that can only use metha- by streaking on brain heart infusion (BHI) plates nol, methylamine, dimethyl amine or DM§ as energy supplemented with 1.5% NaCl. and carbon sources. Hydrogen sulfide can be used as --".-.. "I--,. -..I$-+- ' an energy somce. TI-:---.I$1 ~l~vaulla~e + 1 aLii&l Lllail aullaLb i3 tne end product of sulfide oxidation. As M, sulJido- vorans is considered to be a representative bacterium DMS from the headspace of the cultures was for aerobic DMS oxidation in marine microbial measured with a gas chromatograph wlth a sulfur- mats, its kinetic properties could be used to predict specific, fiame photometric detector, equipped with a the effect of Has on DMS degradation in sit=, using Hayesep R column [9j. Thc detection limitwas 0.5 a previously published (mathematical) compartment ppm in the gas phase. This detection method also model [9]. served lor semi-quantitative H2S measurements in In this paper we report on the extension of the serum bottles with M. suljidovorans and with sedi- model with physiological data on H2S inhibition ment samples. The detection limit was 100 pmol on DM§ oxidation. The breakdown of DMS in the I-' in the liquid phase at pH = 7. presence of hydrogen sulfide was studied in batch Oxygen consumption rates by bacterial suspen- and continuous cultures of M. sulJidovorans. The in- sions were measured with a polarographic Clark- hibitory effect of Hz§ on DM§ oxidation in the pure type electrode in a well-mixed Biological Oxygen culture was compared with observations obtained Monitor at 28°C. The oxygen concentration m the with crude enrichments of fresh microbial mat sam- headspace of serum bottles filled with sediment sam- ples. These results of the crude enrichment cultures ples was measured with a Fisons Instruments (8000 J. M. IM. de Zxurt, J G. Kuenen l FEMS 1Micrcbiology Ecologj~22 (1997) 155--165 157 series) gas chromatograph equipped with a molecu- optical denslty (OD, 430 nm) was correlated linearly lar sieve 5A packed column. with the dry weight (DW) and thc organlc carbon Thiosulfate was determined according to Sorbo analys~s(TOC) of these cultures. ?he correlation [14].Sulfide was determined by iodometric titration was. DW (mg 1-1)=194xOD+14 (r=096, n= 15) for sulfide concentrations higher than 1 mmol I-' (detection limit 0.1 mmol I-') [l5]; and by the meth- 2.5. Oxygen and N2S consumption by ylene blue xethod for sul5de concentrations lower ?d. sulJidovorans with and without DMS than 1 mmol 1-"detection limit 1 pmol I-') 1161. Biomass was determined as organic carbon using Cells used for oxygen and H2Suptake experiments total organic carbon anajysis with a Tocamaster type were cultivated in continuous cultures with miiicral 815-B. The carbon content of M. su@dovorans was medium with DMS (2-3 mmol 1-I) as the sole sub- Downloaded from https://academic.oup.com/femsec/article/22/2/155/541232 by guest on 27 September 2021 50% (w) [9]. Biomass was also measured by dry strate. H2S uptake 1.vas detemined in vials fi!!ed with weight determinations [9]. 5 ml cell suspension and sealed with butyl rubber At the pH of the experiments, sulfide will be pres- septa. Cells were centrifuged (1 0000 X g) and resus- ent as HS- and H2S. These two forms will be re- pended in 25 :5 mmol I-' carbonate:HEPES buffer in ferred to as 'sulfide' or 'H2S7. Sulfide was always 15 g I-' NaCI. DMS (100 ymol I-') was added with added to media as a solution of Na2S.8H20. a syringe. At time=O, 25 ymol 1-' Na2S.8F120 CpH=8) was added. This low concentration of sul- fide was chosen io prevent cheniical oxidaiioii (see Section 2.6). The disappearance rate of sulfide was M. sulJidovorans was cultivated in batch and chem- then measured by stopping the reaction with zinc ostat cultures. Batch cultures in mineral medium acetate (in acetic acid) solution at different time in- supplemented with 10 mmol 1 ' methanol were tervals. The oxygen uptake rate of cell suspension made at 25OC at a pH of 7.5 k0.5 in flasks on a taken directly from the chemostat was measured in rotary shaker at 100 rpm.
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