The Microbial Assemblages And Identification Of Novel Functional Genes In Petroleum Reservoirs

Petroleum reservoirs are generally characterized by special environments. Investigation of the microorganisms living in these environments is of great interest for the oil industry. The rapid progress of PCR-based molecular techniques focused on 16S rRNA gene has led to an in-depth characterization of the microbial communities associated with petroleum reservoirs.In this study, production waters collected from 3 oilfields (6 blocks) in China were examined for bacterial and archaeal composition by means of 16S rRNA gene as a phylogenetic metric. Results show that archaeal libraries were mainly represented by methanogens belonging to members of the genera Methanomethylovorans, Methanosaeta, Methanothermobacter, Methanolinea and Methanoculleus among which hydrogenotrophic methanogens were the most commonly encountered. In addition, archaeal sequences related to candidate divisions lacking cultivated representatives were also detected in our samples. Moreover, archaebacteria sequences related to genera Themococcus, Halogeometricum and Thermogymnomonas were found in the production waters albeit in low density. Within the bacteria domain, Proteobacteria-related phylotypes were the most commonly retrieved from total communities DNA. Other bacterial representatives included members of the Firmicutes, Bacteroidetes, Actinobacteria and Thermotogae. In general we observed that temperature was one of the main factors influencing the diversity of microorganisms within the oil reservoirs. Less diverse bacteria diversity was observed within samples having high salinity while the contrary was true for samples with low salinity.In order to deepen the knowledge about potential function of the microorganisms in the oil reservoir production fluids, an assay targeting a 523 bp fragment within the ASS alpha-subunit (assA) was used to detect the presence of putative alkylsuccinate synthase genes in the samples. Molecular cloning and sequencing of the targeted fragment resulted in the detection novel assA genes. For the first time, assA genes are reported in production waters from oil reservoirs. The detection of catabolic genes involved in the anaerobic degradation of alkanes (assA) allow us to speculate on the presence of a large diversity of anaerobic oil alkane degraders using fumarate addition as the biochemical activation strategy.These findings will be helpful to understand the factors that govern anaerobic biodegradation processes prevailing in petroleum reservoirs.