Anaerobic Consumers of Monosaccharides in a Moderately Acidic Fen

Abstract

16S rRNA-based stable isotope probing identified active xylose- and glucose-fermentingBacteriaand activeArchaea, including methanogens, in anoxic slurries of material obtained from a moderately acidic, CH₄-emitting fen. Xylose and glucose were converted to fatty acids, CO₂, H₂, and CH₄under moderately acidic, anoxic conditions, indicating that the fen harbors moderately acid-tolerant xylose- and glucose-using fermenters, as well as moderately acid-tolerant methanogens. Organisms of the familiesAcidaminococcaceae,Aeromonadaceae,Clostridiaceae,Enterobacteriaceae, andPseudomonadaceaeand the orderActinomycetales, including hitherto unknown organisms, utilized xylose- or glucose-derived carbon, suggesting that highly diverse facultative aerobes and obligate anaerobes contribute to the flow of carbon in the fen under anoxic conditions. UnculturedEuryarchaeota(i.e.,MethanosarcinaceaeandMethanobacteriaceae) andCrenarchaeotaspecies were identified by 16S rRNA analysis of anoxic slurries, demonstrating that the acidic fen harbors novel methanogens andCrenarchaeotaorganisms capable of anaerobiosis. Fermentation-derived molecules are conceived to be the primary drivers of methanogenesis when electron acceptors other than CO₂are absent, and the collective findings of this study indicate that fen soils harbor diverse, acid-tolerant, and novel xylose-utilizing as well as glucose-utilizing facultative aerobes and obligate anaerobes that form trophic links to novel moderately acid-tolerant methanogens.