Comparative analysis of bacterial community and functional species in oil reservoirs with different in situ temperatures

Temperature is supposed to be one of the primary drivers for the bacterial diversification as well as hydrocarbon formation process of oil reservoirs. However, the bacterial community compositions are not systematically elucidated in oil reservoirs with different temperatures. Herein, the diversity of indigenous bacteria and the functional species in the water samples from oil reservoirs with different in situ temperatures was investigated by high-throughput sequencing technology. The results showed that samples in the high (65 degrees C) and super high (80 degrees C) temperature oil reservoir had significantly high bacterial richness, even more than twice as much as moderate temperature (36 degrees C) ones, which showed relatively high bacterial diversity. Meanwhile, the bacterial compositions were almost similar in the high temperature oil reservoirs but there were different relative abundances of the bacterial communities. Phylogenetic analysis revealed that indigenous bacteria fell into 20 phylotypes in which Proteobacteria were the principal phylum in all of samples. At the genus level, 10 out of 22 major genera displayed statistically significant differences. Among of them, Pseudomonas was extremely dominant in all of samples, while Halomonas, Caldicoprobacter, Arcobacter, and Marinobacter tended to be enriched in the high temperature oil reservoirs. Moreover, the abundance of bacterial populations exhibited important distinction in oil reservoir such as hydrocarbon-oxidizing, fermentative, nitrate-reducing, sulfate-reducing, and methanogenic bacteria. Those bacteria were strongly correlated to in situ temperature variation.