Poster, 14th International Symposium on Microbial Ecology - ISME 12, Copenhagen, Denmark: 2012-08-19 - 2012-08-24
Peatlands are a major source of the greenhouse gas methane and their response to global warming and increasing aerial sulphur pollution is one of the largest unknowns in the upcoming decades to centuries. Although regarded as primarily methanogenic environments, biogeochemical studies revealed a hidden sulphur cycle in peatlands which causes rapid renewal of the small standing pool of sulphate. As a consequence, dissimilatory sulphate reduction, which is thermodynamically favoured relative to fermentative and methanogenic processes, often occurs at rates comparable to marine surface sediments and thus effectively decreases gross methane production in peatlands. Our previous work revealed that a * Desulfosporosinus* species belonging to the ‘rare biosphere’ has the potential to substantially contribute to sulphate reduction in a minerotrophic peatland. In addition, analysis of the functional marker genes *dsrAB* [encoding subunit A and B of the dissimilatory (bi)sulphite reductase] revealed a large diversity of putatively novel peatland sulphate-reducing microorganisms (SRM). To illuminate substrate preferences of peatland SRM, we amended anoxic peat-soil slurries regularly with in situ concentrations of single substrates and sulphate and followed sulphate reduction using the 35S-sulphate radiotracer assay. In short-term incubations (6 days), sulphate reduction was stimulated best with lactate, propionate, and butyrate but not with acetate or formate, whereas in long-term incubations (27 days), sulphate reduction was observed under all substrates tested including controls where only endogenous substrates were available. As expected, methane production was drastically reduced in peat-soil slurries amended with sulphate, independent of the tested substrate. Our data indicate that peatland SRM are in involved in a wide range of carbon degradation pathways, either directly or indirectly via syntrophy, with their specific activity depending on the timing of substrate and sulphate availability. In order to elucidate the individual role of selected SRM in the degradation of the various carbon substrates, we are using specific 16S rRNA (gene) and *dsrAB*-targeted quantitative PCR assays to monitor their growth and transcriptional response in the peat-soil incubations.