Ecophysiology and microbial interactions of facultatively anaerobic, dissimilatory sulfate-reducing Acidobacteriota

• Applicant: Professor Dr. Michael Pester
• Subject Area: Microbial Ecology and Applied Microbiology
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 542529277

Most sulfate reducing microorganisms (SRM) gain energy from the reduction of sulfate to sulfide via the Dsr-pathway, a process that drives the biogeochemical sulfur cycle. Sulfate reduction accounts for one third of organic matter mineralization in the global seabed. In anoxic freshwater sediments and peatland soils, SRM drive a cryptic but highly active sulfur cycle and exert control on the production of the potent greenhouse gas methane. Our recent research could show that the known diversity of Dsr-pathway encoding microorganisms massively extends beyond cultured SRM representatives and spans 23 bacterial and 4 archaeal phyla. Members of the Acidobacteriota hold the largest share of this yet to be characterized biodiversity of newly discovered SRM and sustain major Dsr-pathway encoding populations in marine and freshwater settings. Using a continuously operated bioreactor inoculated with peat soil, we could further show that Dsr-pathway encoding Acidobacteriota can switch between sulfate reduction and aerobic respiration while degrading the plant polysaccharide pectin. These results highlighted an unprecedented metabolic flexibility among SRM. This proposal aims to characterize in detail the ecophysiology of sulfate-reducing Acidobacteriota and how they interact with their environment. Three hypotheses will be tested in three work packages (WP): (i) in situ relevant organic polymers other than pectin can be utilized by sulfate reducing peatland Acidobacteriota, (ii) the latter are tightly interacting with so far unidentified members of the microbial community to sustain the cryptic sulfur cycle in peatlands, and (iii) Dsr-pathway encoding Acidobacteriota can have similar functions in marine sediments as in peatlands. WP1 will characterize the ecophysiology of facultative anaerobic, sulfate-reducing Acidobacterium MAG CO124 that was previously enriched in our bioreactor from a peatland. Growth and activity will be followed in response to various plant polysaccharides, different O2 regimes, and different pH. WP2 will focus on inter-species microbial interactions to understand the sulfur cycle in our bioreactor setting, specifically sulfur compound-oxidizing and disproportionating processes. We will quantify all sulfur cycle intermediates, characterize the activity of sulfur compound-oxidizing and -disproportionating microorganisms, and determine how they interact with sulfate reducing Acidobacterium MAG CO124. In WP3, a bioreactor will be inoculated with marine sediments and operated under alternating anoxic and oxic conditions as well. Here, we will test if Dsr-pathway encoding Acidobacteriota from marine environments can fulfill similar functions as their counterparts in peatlands. Such flexibility could be key to compete with the overwhelming dominance of the Desulfobacterota in marine sediments. The proposed project will be important to understand the ecological role of this widespread and abundant group of newly discovered SRM.

• DFG Programme: Research Grants