Effects of environmental factors on the abundance and distribution of methane-oxidizing bacteria in typical oil and gas reservoirs

Abstract:

[Objective] Methane-oxidizing bacteria (MOB) are crucial indicators in the microbial exploration of oil and gas reservoirs, while their diversity and distribution are influenced by geographical location and environmental factors. This study aims to explore the effects of environmental variations on the abundance and distribution of MOB in the soil samples collected from seven representative areas in typical oil and gas reservoirs. [Methods] Soil samples were subjected to real-time fluorescence quantitative PCR (qPCR) for pmoA and sequencing of bacterial 16S rRNA gene and pmoA. The abundance of MOB was compared among different samples, on the basis of which the impacts of environmental factors on the distribution of MOB were analyzed. [Results] The highest water content (approximately 22.8%) was detected in the samples from the Jianghan Basin. The average content of nitrate nitrogen was highest in the Yubei oil field, reaching approximately 31.96 μg/g. The Chunguang oil field showcased the highest concentrations of SO₄^2- (6 425.0 mg/g) and Cl^- (1 617.0 mg/g). The qPCR results revealed that the pmoA in MOB accounted for only 0.77% of that in total soil bacteria, indicating the low absolute abundance of MOB in the soil. The 16S rRNA gene sequencing identified three type I MOB genera (Methylosarcina, Methylocaldum, and Methylococcus) and one type II MOB genera (Methylocystis). However, the dominant genera in the MOB had extremely low relative abundance, with the maximum of 0.124%. Sequencing of pmoA revealed that Methylocystis and Methylosinus, two genera of type II MOB, were dominant. The absolute abundance of MOB showed significant correlations with ammonium nitrogen, pH, particle size, SO₄^2-, and Cl^-. The relative abundance of MOB had significant correlations only with particle size, total nitrogen, total phosphorus, and metal ions (Al, Fe, K, Ca, Mg, Mn, Zn, and Cu). The discriminant correlation analysis (DCA) indicated that soil moisture, pH, soil particles<2 μm, total nitrogen, and Ca²⁺ significantly influenced the composition of the functional gene pmoA in MOB. [Conclusion] This study analyzed the absolute and relative abundance of MOB in soil samples from seven typical oil and gas reservoirs. The MOB abundance showed significant differences depending on the measurement method used. The 16S rRNA gene sequencing fails to comprehensively reflect the community structure of MOB in the soil samples. Different geographical locations showed variations in MOB communities, and no specific indicator communities were detected for oil and gas reservoirs or background sites on a national scale. The correlation analysis between environmental factors and MOB revealed that the environmental factors had different effects on the absolute and relative abundance of MOB.