Microbial Populations Involved in Cycling of Dimethyl Sulfide and Methanethiol in Freshwater Sediments

Abstract

Although several microorganisms that produce and degrade methanethiol (MT) and dimethyl sulfide (DMS) have been isolated from various habitats, little is known about the numbers of these microorganisms in situ. This study reports on the identification and quantification of microorganisms involved in the cycling of MT and DMS in freshwater sediments. Sediment incubation studies revealed that the formation of MT and DMS is well balanced with their degradation. MT formation depends on the concentrations of both sulfide and methyl group-donating compounds. A most-probable number (MPN) dilution series with syringate as the growth substrate showed that methylation of sulfide with methyl groups derived from syringate is a commonly occurring process in situ. MT appeared to be primarily degraded by obligately methylotrophic methanogens, which were found in the highest positive dilutions on DMS and mixed substrates (methanol, trimethylamine [TMA], and DMS). Amplified ribosomal DNA restriction analysis (ARDRA) and 16S rRNA gene sequence analysis of the total DNA isolated from the sediments and of the DNA isolated from the highest positive dilutions of the MPN series (mixed substrates) revealed that the methanogens that are responsible for the degradation of MT, DMS, methanol, and TMA in situ are all phylogenetically closely related to Methanomethylovorans hollandica. This was confirmed by sequence analysis of the product obtained from a nested PCR developed for the selective amplification of the 16S rRNA gene from M. hollandica. The data from sediment incubation experiments, MPN series, and molecular-genetics detection correlated well and provide convincing evidence for the suggested mechanisms for MT and DMS cycling and the common presence of the DMSdegrading methanogen M. hollandica in freshwater sediments.The cycling of dimethyl sulfide (DMS) and methanethiol (MT) has been intensively studied due to the impact the oxidation products of these compounds (e.g., methanesulfonic acid and SO 2 ) have on the processes of global warming, acid precipitation, and the global sulfur cycle (1,3,24). Previous research revealed that MT and DMS were the dominant volatile organic sulfur compounds (VOSC) in freshwater sediments and water columns (20). Fluxes of MT and DMS to the atmosphere depend on the steady-state concentrations of these compounds in the sediment and water surface layers. These steady-state concentrations are the result of biological (and chemical) production and degradation. Various studies reported that microbial production and degradation of these VOSC in freshwater, marine, estuarine, and salt lake sediments are relatively well balanced (15-18, 20-23; B. P. Lomans, J.-J. Wesselink, P. Bakkes, A. Pol, C. van der Drift, and H. J. M. Op den Camp, submitted for publication). In anaerobic freshwater sediments, formation of MT and DMS has been demonstrated to occur mainly by methylation of sulfide (7,(20)(21)(22)(23) Lomans et al., submitted) and to a lesser extent by the degradation of sulfur-containing amino acids (14...

Methanotrophic symbionts provide carbon for photosynthesis in peat bogs

“…16S rRNA gene sequence analysis, FISH and electron microscopy. Total genomic DNA from S. cuspidatum plants containing methanotrophs, isolated with combined methods 17 , was used as template for PCR amplification of 16S rRNA genes. PCR was performed with general bacterial primers 18 using a T gradient thermal cycler (Biometra), and a clone library was made as described previously 18 .…”

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