Anaerobic trophic interactions of contrasting methane-emitting mire soils: processes versus taxa

Natural wetlands such as mires contribute up to 33% to the global emission of methane. The emission of methane is driven by trophic interactions of anaerobes that collectively degrade biopolymers. The hypothesis of this study was that these interactions in contrasting methane-emitting mire soils are functionally similar but linked to dissimilar taxa. This hypothesis was addressed by evaluating anaerobic processes and microbial taxa of eutrophic, mesotrophic and oligotrophic mire soils. Glucose was fermented to various products (e.g. H-2, CO2, butyrate, acetate). Acetoclastic methanogenesis occurred, and acetogenesis and methanogenesis transformed H-2-CO2 to acetate and methane, respectively. Although product profiles, cultivable cell numbers and gene copy numbers [mcrA (encodes alpha-subunit of methyl-CoM reductase) and 16S rRNA genes] were similar for all mire soils, only approximately 15% of detected family-level bacteria and species-level methanogens were shared by all mire soils. Approximately, 40% of the detected family-level taxa of each mire soil have no cultured isolates. Acidic conditions appeared to restrict the number of dominant phylotypes. The results indicated (a) that microbial processes which drive methanogenesis are similar but facilitated by dissimilar microbial communities in contrasting mire soils and (b) that mire soils harbor a large number of taxa with no cultured isolates.