Characterizing the metatranscriptomic profile of archaeal metabolic genes at deep-sea hydrothermal vents in the Mid-Cayman Rise

Deep-sea hydrothermal vent systems host a wide diversity of bacteria, archaea and viruses. Although the geochemical conditions at these vents are well-documented, the relative metabolic activity of microbial lineages, especially among archaea, remains poorly characterized. The deep, slow-spreading Mid-Cayman Rise, which hosts the mafic-influenced Piccard and ultramafic-influenced Von Damm vent fields, allows for the comparison of vent sites with different geochemical characteristics. Previous metagenomic work indicated that despite the distinct geochemistry at Von Damm and Piccard, the functional profile of microbial communities between the two sites was similar. We examined relative metabolic gene activity using a metatranscriptomic analysis and observed functional similarity between Von Damm and Piccard, which is consistent with previous results. Notably, the relative expression of the methyl-coenzyme M reductase (mcr) gene was elevated in both vent fields. Additionally, we analyzed the ratio of RNA expression to DNA abundance of fifteen archaeal metagenome-assembled genomes (MAGs) across the two fields. Previous work showed higher archaeal diversity at Von Damm; our results indicate relatively even expression among archaeal lineages at Von Damm. In contrast, we observed lower archaeal diversity at Piccard, but individual archaeal lineages were very highly expressed; Thermoprotei showed elevated transcriptional activity, which is consistent with higher temperatures and sulfur levels at Piccard. At both Von Damm and Piccard, specific Methanococcus lineages were more highly expressed than others. Future analyses will more closely examine metabolic genes in these Methanococcus MAGs to determine why some lineages are more active at a vent field than others. We will conduct further statistical analyses to determine whether significant differences exist between Von Damm and Piccard and whether there are correlations between geochemical metadata and metabolic gene or archaeal MAG transcription. These efforts will lead to a better understanding of the metabolic characteristics of ancient archaea and the extent to which vent geochemistry influences local microbial metabolic profiles.