Molecular diversity and abundance of the microbial community associated to an offshore oil field on the southeast of Brazil

Petroleum microbiology is important to the fossil oil industry and any related environmental research. Assessment of resident microbial communities is essential for controlling many technical, operational, and environmental issues. However, difficulties of sampling and extraction are limiting factors. Herein, we assessed the bacterial and archaeal population of sulphate-reducing microorganisms (SRM) in a production water from an industrial setting with corrosion signals, within a Brazilian offshore oil reservoir. Four hypervariable regions of 16S rRNA gene were sequenced, while dsrA gene was quantified by RT-qPCR to estimate the SRM abundance. Results showed that richness and diversity of were greater in bacteria than archaea population, revealing a domination of Desulfobacterota and Nanoarchaeota phyla, respectively. RT-qPCR analyses indicated that dsrA reached 2.65 ? 103 copies.ml- 1, which is consistent with the relative abundance of bacteria/archaea methanogens detected by 16S analyses. The content of methanogen archaea suggested a relatively low abundance of these organisms. Despite the strategic and economical importance of the Campos Basin, little is known about the complexity of the microbial communities present in its oil field food chain, and our results have expanded the knowledge of that environment, highlighting its complexity.