Succession of Deferribacteres and Epsilonproteobacteria through a nitrate-treated high-temperature oil production facility.

Members of Epsilonproteobacteria and Deferribacteres have been implied in nitrate-induced souring control in high-temperature oil production facilities. Here we report on their diversity and abundance in the injection and production part of a nitrate-treated, off-shore oil facility (Halfdan, Denmark) and aimed to assess their potential in souring control. Nitrate addition to deoxygenated seawater shifted the low-biomass seawater community dominated by Gammaproteobacteria closely affiliated with the genus Colwellia to a high-biomass community with significantly higher species richness. Epsilonproteobacteria accounted for less than 1% of the total bacterial community in the nitrate-amended injection water and were most likely outcompeted by putative nitrate-reducing, methylotrophic Gammaproteobacteria of the genus Methylophaga. Reservoir passage and recovery of the oil resulted in a significant change in the bacterial community. Members of the thermophilic Deferribacteres were the second major fraction of the bacterial community in the production water (~30% of the total bacterial community). They were not found in the injection water and were therefore assumed to be indigenous to the reservoir. Additional diversity analysis and targeted quantification of periplasmic nitrate reductase (napA) genes indicated that most resident Deferribacteres possessed the functional potential to contribute to nitrate reduction in the system. In sum, the dominance of nitrate-reducing Deferribacteres and the low relative abundance of Epsilonproteobacteria throughout the production facility suggested that the Deferribacteres play a major role in nitrate-induced souring control at high temperatures.