Microbial sulfur cycling in a sulfidic cave

摘要

A sulfur-oxidizing microbial community in a sulfidic cave stream was examined for evidence of anaerobic microbial populations that may contribute to the sulfur biogeochemistry. Culture-dependent methods were used to enumerate the anaerobic metabolic guilds, and these results were evaluated in context with the aerobic sulfur-oxidizing bacterial (SOB) community, water chemistry, and the results of microcosm experiments.We found a dynamic and diverse anaerobic community; stream microbial mats supported fermenters and sulfatereducing bacteria (SRB), with scant methanogens. Autochthonous reduced sulfur compounds were produced by SRB, which adds significant additional sulfide for SOBs. These results suggest that fermenting microbes process carbon fixed by autotrophic oxidizers, supplying SRB populations with organic carbon substrate. Sufficient sulfate from the stream and SOB is available to support SRB activity, while suppressing methanogenic activity.The net ecosystem result is the continuous production of sulfide supporting autotrophic SOB, and extending the microbial mat, potentially influencing cave formation.