Methane-related community of a carbonate-enriched pockmark, Brazilian Southeastern continental slope

Abstract

Pockmarks are geological features that often sustain hydrocarbon-related communities of microorganisms when active, seeping oil or methane. Microbial communities of inactive pockmarks have not been well studied until the present. Plenty of pockmarks in the Southwestern Atlantic Ocean have been discovered. However, no information is available about the organic characteristics in association with the microbial diversity related to methane and non-methane hydrocarbon consumption. This study examined the identity and potential ecology of the methane-related microbial community in an inactive SW Atlantic Carbonate-enriched Pockmark (SWACP). Undisturbed sediment cores were enriched with CH₄ 99.5% at 5°C, with samples harvested at 16h, 120h, 240h, 720h, and 960h, followed by metataxonomics functional prediction, and the correlation of microbial groups with incubation and enrichment types. The SWACP is depleted in organic compounds, and chemosynthetic production is dominant. Incubated mini-cores of sediment were affected by incubation time and enrichment type, which influenced the microbial composition. Although several taxa were shared among all sediment samples, specific groups per enrichment type and incubation time were observed. These communities comprised taxa previously reported in marine bottom waters, carbonate crusts, active cold-seeps, and inactive pockmarks. The methane-enriched taxa were predominantly related to aerobic methanotrophy, methylotrophy, aerobic and anaerobic non-methane hydrocarbon degradation, and fermentation. This study brings the first survey of the key microbial groups in methane fluxes of a Brazilian deep-sea pockmark, providing data for understanding the ecology surrounding the SW Atlantic gas field areas.

Descriptors: 16S rRNA gene; hydrocarbon; Methanotrophs; Methylotrophs; Fermenters