The importance of Clostridia to microbial community processes in oil reservoirs has mostly been ignored. Here we present data on an abundant, spore forming Clostridia organism found in producing wells from the Galveston 209 field, offshore Gulf of Mexico. These reservoirs have temperatures greater than 100 °C and salinity values exceeding 28. Metagenome assembled genomes (MAG) were retrieved from metagenomic assemblies of Illumina reads from each of the four sampled reservoirs. Completeness based on the presence of marker genes, ranged from 99.2% to 100.0%. Based on phylogenetic analyses of both 16S rRNA genes and concatenated ribosomal proteins, this Clostridia is closely related, but distinct from to Caminicella sporogenes and Clostridium caminithermale (aka Paramaledivibacter caminithermalis). Both of these cultured organisms are at least moderately thermophilic and halophilic and were initially isolated from deep-sea hydrothermal vent systems. Given the thermophilic nature of these relatives, it is unlikely that our MAGs contain a mesophilic pipeline or infrastructure contaminant. Metabolic pathways found in Galveston 209 MAGs were similar to those found in C. sporogenes and C. caminithermale, which are anaerobic fermenters of carbohydrates and proteinaceous substances, producing products such as H2, CO2, acetate, formate, butyrate, and other volatile fatty acids. The MAGs did include some differences not found in their cultured relatives, including a complete Wood-Ljungdahl carbon fixation pathway, additional sulfur processing genes, and differences in carbohydrate processing genes. For example, the Galveston organisms metabolize sucrose, unlike the two cultured organisms, while the cultured ones take up cellubiose, but the Galveston ones cannot. Sporulation pathways were found in both the Galveston MAGs and the cultured relatives. Although spore formation may have initially helped the Galveston Clostridia resist the high temperatures of this reservoir system, 35-40% of the community appear to be in the process of replicating. The Galveston MAGs may then represent a distinct adaption of the moderately halophilic and thermophilic Caminicella (Para)maledivibacter group to the higher temperatures found in the Galveston system. Though there is no evidence that any of these organisms are directly metabolizing hydrocarbons found in these reservoirs, the worldwide occurrence of clostridial organisms in oil reservoirs should not be ignored.

Clostridia in hot oil reservoirs of Texas

2019 Spring National Meeting

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