Bathyarchaeia occurrence in rich methane sediments from a Brazilian ria

Previous studies reported methane gas (CH4) reservoirs in Saco do Mamangu ' a ria marine sediments (Rio de Janeiro, Brazil). Knowing that methane-related microbiomes are still poorly characterized in methane-rich tropical shallow sites, this study aimed to investigate microbial communities' diversity and spatial distribution in the sediments of Saco do Mamangu ' a ria. For this purpose, we collected sediment samples through 100 cm long gravity corer at three sites to perform community analysis based on 16S rRNA gene sequencing, quantification of the methyl coenzyme M reductase-encoding gene (mcrA), and geochemical analysis, including CH4 stable isotope. Our results revealed a biogenic trend for CH4 isotopic signature and a high proportion of archaeal sequences assigned to the class Bathyarchaeia (phylum Crenarchaeota), with a spatial distribution throughout the channel's inner areas and the deepest strata. Operational taxonomic units (OTUs) classified within class Bathyarchaeia and Dehalococcoidia showed a positive correlation with CH4 concentrations, sediment depth, and oxidation-reduction potential. Due to their prevalence in the microbial community, we also performed a phylogenetic analysis to understand the Bathyarchaeia OTUs' affiliation with the Bathyarchaeia subgroups. The results showed a closer affiliation with Bathy-8 and Bathy-13 subgroups, previously proposed as indicators for marine and estuarine anoxic sediments, respectively. Our results emphasize the importance of the ecological role potentials of Bathyarchaeia subgroups in methane-rich tropical coastal ecosystems carbon cycling.

Automated summary

This study investigated the diversity and spatial distribution of microbial communities in the sediments of Saco do Mamangu'aria in Rio de Janeiro, Brazil, revealing a positive correlation between archaeal sequences and CH4 concentrations, sediment depth, and oxidation-reduction potential. The results underscore the importance of Bathyarchaeia subgroups in carbon cycling in methane-rich tropical coastal ecosystems.