BayCEER Workshop 2020

Cues for a microbial link between the cycling of methane and iodine in cave biofilms

The cave of an iodine-rich spring in southern Germany is inhabited by extensive microbial biofilms. Microorganisms in these biofilms feed on geogenic exhalations of methane as the primary source of carbon and energy in the cave. Calculated Gibbs free energy yields suggest that the microbial consumption of methane could be driven by the reduction of a variety of different electron acceptors, including O₂, NO₃^-, Fe(III), and even iodate. Our ongoing investigations focus on (i) exploration of the biofilm metabolic potentials, (ii) discovery of novel methanotrophic taxa, and (iii) identification of postulated metabolic links between the cycling of iodine species and methane. Metagenome sequencing of submersed and subaerial biofilms revealed that microbial communities in the cave were dominated by diverse methanotrophic and methylotrophic taxa, as well as members of the putatively denitrifying, methanotrophic NC10 candidate phylum. De novo assembly and binning of the metagenomic data yielded about 40 near complete genomes harboring diverse metabolic potentials, including complete pathways for methanotrophy, denitrification and haloalkane degradation. Latter may serve as a potential proxy for the microbial turnover of reactive iodine species, including iodomethane. A planned combination cultivation and stable carbon isotope tracer experiments will help to identify and cultivate microorganisms potentially involved in the coupled cycling of methane and iodine.