The ties that bind: Dynamics of syntrophic associations in marine methane seeps

Abstract

The deep-sea methane seep environment supports active and diverse microbial assemblages supported by the anaerobic oxidation of methane (AOM). Unknown to science less than a decade ago, the microorganisms and the molecular mechanisms underlying this enigmatic and globally important biogeochemical process have been the subject of intensive study worldwide. The identification, activity, distribution, and partial metabolic pathway reconstruction of methanotrophic archaea and co-associated sulfate reducing bacteria has been characterized. However fundamental questions still remain regarding the necessity of a physically coupled syntrophic association between sulfate reducing bacteria and methane oxidizing archaea, the underlying biochemistry enabling sulfate-coupled methane oxidation, and the extent of the diversity of microbial assemblages involved in AOM. Using microanalytical stable isotope analyses of whole cells in tandem with genomics enabled molecular methods, we examined the variation in metabolic activity between individual aggregations of microorganisms recovered from methane seep sediments. Significant differences in activity were observed between archaeal-bacterial associations and mono-specific aggregations of putative methanotrophic archaea and sulfate-reducing populations, supporting enhanced metabolism in multi-species aggregates. Application of a new SSU rRNA targeted method for capturing and concentrating specific uncultured microbial populations from methane seep sediments has uncovered novel partnerships and additional insights into the metabolic potential of the methanotrophic archaea and co-associated bacteria.

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