The wetland sulfur microbiome

Wetlands are responsible for about a third of the global annual emission of the potent greenhouse gas methane and are key ecosystems in global carbon cycling and climate change. Sulfur-cycling microorganisms have an important but undervalued role in organic matter degradation and controlling methane emissions from wetlands by diverting the carbon flow away from methane- producing archaea. While a few studies provided first insights into the identity and ecological role of sulfate-reducing bacteria, microorganisms involved in the various individual steps of sulfur cycling in wetlands are under-characterized. A deeper understanding of microbial ecology in wetlands is necessary for assessing how the microbial communities in these vulnerable ecosystems will respond to future climate changes such as rising global temperature. This project thus aims at establishing the first comprehensive overview of the sulfur microbiome in wetlands. Selected research questions that will be addressed are: What is the identity and ecophysiology of microorganisms that reduce or oxidize sulfur compounds of intermediate oxidation states, e.g. sulfite, thiosulfate, tetrathionate, elemental sulfur, for energy generation? What is the physiological interplay between generalists that utilise diverse sulfur compounds of various oxidation states and specialists that utilise only selected sulfur compounds? How is sulfur metabolism in wetland microorganisms linked to complementary utilization of compounds of other element cycles such as carbon, nitrogen, and iron? We will initially draw on available metagenome, metatranscriptome, and supporting biogeochemical data from diverse native wetlands or wetland experiments to establish a genome collection of uncultured sulfur microorganisms and reveal their putative physiological functions and interspecies interactions. Genome-based physiological predictions will be evaluated through monitoring microbial activities in a series of defined soil microcosm experiments by molecular biology, stable isotope probing, and biogeochemical analyses. The combination of modern genome-centric and strain-level Omics approaches with experiments designed to test specific metabolic hypotheses will lead to a better understanding of the identity and distribution of sulfur-cycling microorganisms and the physiological mechanisms that allow them to provide central ecosystem services in the different wetlands.