Sulfuric acid caves are rare karst systems in which carbonate dissolution is driven to a large extent by the oxidation of hydrogen sulfide (H2S) to sulfuric acid. In these caves, substantial corrosion occurs above the water table where H2S gas volatilizes from sulfidic cave streams and is oxidized to sulfuric acid on subaerial cave surfaces. H2S oxidation is catalyzed by diverse chemolithotrophic microorganisms that colonize cave walls and produce distinctive biofilms and mineralogical features. In order to learn more about the sulfide-oxidizing microorganisms that are important for speleogenesis above the water table, we sequenced multiple metagenomes from different cave surfaces and are experimenting with strategies to recover metagenome-assembled genomes from these datasets. In one project, we combined a short-insert (3-8 Kbp) Pacific Biosciences (PacBio) library with short-read Illumina data to improve assembly and binning from metagenomes of highly acidic “snottite” biofilms from Cueva de Villa Luz, Tabasco, Mexico. Snottites are typically pH 0-1 and occur in immediate proximity to H2S-degassing streams. Preliminary analysis indicates that these biofilms contain several populations with the potential to oxidize sulfide, including Acidithiobacillus spp., Metalibacterium spp., and members of the family Acidimicrobiaceae. In a second project, we used Phase Genomics’ ProxiMeta Hi-C technology to generate metagenomes of anastomosing wall sediments known as “biovermiculations” from two locations in the Frasassi cave system, Italy. With the ProxiMeta Hi-C process, DNA from intact microbial cells is cross-linked in situ and sequenced following a proximity ligation procedure that is used to guide assembly and binning. We applied this technique to biovermiculations collected 2 m and 18 m above an actively degassing stream, which are expected to experience very different levels of H2S gas flux. These communities are much more diverse than the snottites and contain numerous potential sulfide oxidizers. We will discuss the diversity and metabolic potential of different sulfide-oxidizing populations based on metagenomic analysis, the implications for microbial sulfide oxidation in sulfuric acid caves, and how these methods of genome recovery compare with that of other metagenomic binning practices.

Improved genome recovery from cave wall metagenomes provides new insights into microbial sulfide oxidation in sulfuric acid caves

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.