Analysis of microbial communities in the oil reservoir subjected to CO2-flooding by using functional genes as molecular biomarkers for microbial CO2 sequestration.

Jin-Feng Liu,Serge M Mbadinga,Xiao-Bo Sun,Bo-Zhong Mu,Guang-Chao Yang,Ji-Dong Gu

doi:10.3389/fmicb.2015.00236

Abstract

Sequestration of CO2 in oil reservoirs is considered to be one of the feasible options for mitigating atmospheric CO2 building up and also for the in situ potential bioconversion of stored CO2 to methane. However, the information on these functional microbial communities and the impact of CO2 storage on them is hardly available. In this paper a comprehensive molecular survey was performed on microbial communities in production water samples from oil reservoirs experienced CO2-flooding by analysis of functional genes involved in the process, including cbbM, cbbL, fthfs, [FeFe]-hydrogenase, and mcrA. As a comparison, these functional genes in the production water samples from oil reservoir only experienced water-flooding in areas of the same oil bearing bed were also analyzed. It showed that these functional genes were all of rich diversity in these samples, and the functional microbial communities and their diversity were strongly affected by a long-term exposure to injected CO2. More interestingly, microorganisms affiliated with members of the genera Methanothemobacter, Acetobacterium, and Halothiobacillus as well as hydrogen producers in CO2 injected area either increased or remained unchanged in relative abundance compared to that in water-flooded area, which implied that these microorganisms could adapt to CO2 injection and, if so, demonstrated the potential for microbial fixation and conversion of CO2 into methane in subsurface oil reservoirs.

Highlights

Storage of CO2 in deep geological formations, such as oil reservoirs, is one of the feasible measures to reducing CO2 emissions into the atmosphere
We found that sequences from microorganisms similar with those from the Firmicutes, Gamma-Proteobacteria, and Thermotogae were the most encountered in clone libraries established for [FeFe]-hydrogenase-encoding gene, and these results are consistent with those of Schmidt et al (2010), who found that members of the order Clostridiales and Thermoanaerobacter sp. were likewise all capable of fermentative production of H2 (Schmidt et al, 2010)
We explored the potential for autotrophic CO2 fixation and bioconversion with microbial communities in oil reservoir by detection of relative functional biomarker genes such as CO2 fixation, acetogenesis, hydrogen formation ([FeFe]-hydrogenase-encoding gene), and methanogenesis

Summary

Introduction

Storage of CO2 in deep geological formations, such as oil reservoirs, is one of the feasible measures to reducing CO2 emissions into the atmosphere. The CBB biochemical process was reported to occur in Proteobacteria, including some members of Firmicutes, Actinobacteria, and Chloroflexi as well as in plants, algae, and cyanobacteria (Ivanovsky et al, 1999; Zakharchuk et al, 2003; Berg et al, 2005; Caldwell et al, 2007; Lee et al, 2009) Another important pathway of CO2 fixation is the reductive acetyl-CoA pathway that has documented to occur in acetogenic prokaryotes, ammonium-oxidizing Planctomycetes (Strous et al, 2006), sulfidogenic bacteria (Schauder et al, 1988), and autotrophic archaea affiliated with the order Archaeoglobales (Vorholt et al, 1995, 1997). This pathway is utilized by acetogenic prokaryotes for energy conservation (Ragsdale and Pierce, 2008; Thauer et al, 2008; Biegel and Muller, 2010)

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