Methane production by Methanothermobacter thermautotrophicus to recover energy from carbon dioxide sequestered in geological reservoirs

Bioconversion Pathway of CO2 in the Presence of Ethanol by Methanogenic Enrichments from Production Water of a High-Temperature Petroleum Reservoir

Transformation of CO2 in both carbon capture and storage (CCS) to biogenic methane in petroleum reservoirs is an attractive and promising strategy for not only mitigating the greenhouse impact but also facilitating energy recovery in order to meet societal needs for energy. Available sources of petroleum in the reservoirs reduction play an essential role in the biotransformation of CO2 stored in petroleum reservoirs into clean energy methane. Here, the feasibility and potential on the reduction of CO2 injected into methane as bioenergy by indigenous microorganisms residing in oilfields in the presence of the fermentative metabolite ethanol were assessed in high-temperature petroleum reservoir production water. The bio-methane production from CO2 was achieved in enrichment with ethanol as the hydrogen source by syntrophic cooperation between the fermentative bacterium Synergistetes and CO2-reducing Methanothermobacter via interspecies hydrogen transfer based upon analyses of molecular microbiology and stable carbon isotope labeling. The thermodynamic analysis shows that CO2-reducing methanogenesis and the methanogenic metabolism of ethanol are mutually beneficial at a low concentration of injected CO2 but inhibited by the high partial pressure of CO2. Our results offer a potentially valuable opportunity for clean bioenergy recovery from CCS in oilfields.

Functional annotation of operome from Methanothermobacter thermautotrophicus ΔH: An insight to metabolic gap filling

Methanothermobacter thermautotrophicus ΔH (MTH) is a potential methanogen known to reduce CO₂ with H₂ for producing methane biofuel in thermophilic digesters. The genome of this organism contains ~50.5% conserved hypothetical proteins (HPs; operome) whose function is still not determined precisely. Here, we employed a combined bioinformatics approach to annotate a precise function to HPs and categorize them as enzymes, binding proteins, and transport proteins. Results of our study show that 315 (35.6%) HPs have exhibited well-defined functions contributing imperative roles in diverse cellular metabolism. Some of them are responsible for stress-response mechanisms and cell cycle, membrane transport, and regulatory processes. The genome-neighborhood analysis found five important gene clusters (dsr, ehb, kaiC, cmr, and gas) involving in the energetic metabolism and defense systems. MTH operome contains 223 enzymes with 15 metabolic subsystems, 15 cell cycle proteins, 17 transcriptional regulators and 33 binding proteins. Functional annotation of its operome is thus more fundamental to a profound understanding of the molecular and cellular machinery at systems-level.

The plasticity of indigenous microbial community in a full-scale heavy oil-produced water treatment plant

Indigenous microbial communities are main and promising performers for bioremediation due to their excellent adaptability, degradation capability, and inherent plasticity. Treating heavy oil-produced water (HOPW) is a challenge owing to the high recalcitrance and heterogeneity of chemicals it contains. A full-scale HOPW treatment plant was built at a capacity of 10,000 m³/d with the indigenous microbial community. After the treatment, the outlet water reached the design standard. The microbial community structures in all treatment stages were analyzed by using Illumina MiSeq 16S rRNA gene sequencing. The composition of microbial community changed greatly with the changes in environmental conditions, especially with the only artificially regulated parameter of dissolved oxygen. In the anaerobic stage, the community converted the recalcitrant chemical oxygen demand to biological oxygen demand (BOD), and played a major role in enhancing the biodegradability of HOPW. During the aerobic stage, the community mainly mineralized BOD. These results suggest that the structures of indigenous microbial community differed in different treatment stages to accomplish the corresponding functions. Based on these findings, it is proposed that exploiting the plasticity of microbial communities for bioremediation is feasible, especially treating wastewater with varied components.