To investigate the spatial distribution of microbial communities and their drivers in petroleum reservoir environments, we performed pyrosequencing of microbial partial 16S rRNA, derived from 20 geographically separated water-flooding reservoirs, and two reservoirs that had not been flooded, in China. The results indicated that distinct underground microbial communities inhabited the different reservoirs. Compared with the bacteria, archaeal alpha-diversity was not strongly correlated with the environmental variables. The variation of the bacterial and archaeal community compositions was affected synthetically, by the mining patterns, spatial isolation, reservoir temperature, salinity and pH of the formation brine. The environmental factors explained 64.22% and 78.26% of the total variance for the bacterial and archaeal communities, respectively. Despite the diverse community compositions, shared populations (48 bacterial and 18 archaeal genera) were found and were dominant in most of the oilfields. Potential indigenous microorganisms, including Carboxydibrachium, Thermosinus, and Neptunomonas, were only detected in a reservoir that had not been flooded with water. This study indicates that: 1) the environmental variation drives distinct microbial communities in different reservoirs; 2) compared with the archaea, the bacterial communities were highly heterogeneous within and among the reservoirs; and 3) despite the community variation, some microorganisms are dominant in multiple petroleum reservoirs.

Sulfate-reducing bacteria (SRB) have been studied extensively in the petroleum industry due to their role in corrosion, but very little is known about sulfur-oxidizing bacteria (SOB), which drive the oxidization of sulfur-compounds produced by the activity of SRB in petroleum reservoirs. Here, we surveyed the community structure, diversity and abundance of SRB and SOB simultaneously based on 16S rRNA, dsrB and soxB gene sequencing, and quantitative PCR analyses, respectively in petroleum reservoirs with different physicochemical properties. Similar to SRB, SOB were found widely inhabiting the analyzed reservoirs with high diversity and different structures. The dominant SRB belonged to the classes Deltaproteobacteria and Clostridia, and included the Desulfotignum, Desulfotomaculum, Desulfovibrio, Desulfobulbus, and Desulfomicrobium genera. The most frequently detected potential SOB were Sulfurimonas, Thiobacillus, Thioclava, Thiohalomonas and Dechloromonas, and belonged to Betaproteobacteria, Alphaproteobacteria, and Epsilonproteobacteria. Among them, Desulfovibrio, Desulfomicrobium, Thioclava, and Sulfurimonas were highly abundant in the low-temperature reservoirs, while Desulfotomaculum, Desulfotignum, Thiobacillus, and Dechloromonas were more often present in high-temperature reservoirs. The relative abundances of SRB and SOB varied and were present at higher proportions in the relatively high-temperature reservoirs. Canonical correspondence analysis also revealed that the SRB and SOB communities in reservoirs displayed high niche specificity and were closely related to reservoir temperature, pH of the formation brine, and sulfate concentration. In conclusion, this study extends our knowledge about the distribution of SRB and SOB communities in petroleum reservoirs.