Jin-Feng Liu,Yu-Wei Lu,Lei Zhou,Wei Li,Zhao-Wei Hou,Shi-Zhong Yang,Xiao-Lin Wu,Ji-Dong Gu,Bo-Zhong Mu
Methanogenic hydrocarbon degradation is an important biogeochemical process in oil reservoirs; however, genomic DNA-based analysis of microorganisms and metabolite detection are not conclusive for identification of the ongoing nature of this bioprocess. In this study, a suite of analyses, involving the study of microbial community and selective gene quantification of both genomic DNA and RNA together with signature metabolites, were performed to comprehensively advance the understanding of the methanogenic biodegradation of hydrocarbons in a low-temperature oilfield. The fumarate addition products for alkanes—C 4 , C 5 , and C 7 -alkylsuccinates—and transcribed assA and mcrA genes were simultaneously detected in the production water sample, providing robust and convincing evidence for both the initial activation of n -alkanes and methane metabolism in this oilfield. The clone library of assA gene transcripts showed that Smithella was active and most likely responsible for the addition of fumarate to n -alkanes, whereas Methanoculleus and Methanothrix were the dominant and active methane-producers via CO 2 reduction and acetoclastic pathways, respectively. Additionally, qPCR results of assA and mcrA genes and their transcribed gene copy numbers revealed a roughly similar transcriptional activity in both n -alkanes-degraders and methane producers, implying that they were the major participants in the methanogenic degradation of n -alkanes in this oilfield. To the best of our knowledge, this is the first report presenting sufficient speculation, through detection of signature intermediates, corresponding gene quantification at transcriptional levels, and microbial community analysis, of methanogenic degradation of n -alkanes in production water of an oil reservoir.
Anaerobic oxidation of methane coupled to nitrous oxide reduction (N 2 O-AOM) is an important microbial pathway for mitigating greenhouse gases. However, it remains largely unknown whether this process could occur in landfills, which are important anthropogenic sources of greenhouse gases emissions. Here, 13 CH 4 was supplied in microcosm incubations to track potential rates for the N 2 O-AOM process in landfill cover soils (LCS). The highest rates for the N 2 O-AOM process were observed in the bottom layers of LCS and it could be remarkably promoted by the addition of electron shuttles. In addition, 2-bromoethanesulfonic sodium inhibited the N 2 O-AOM process and reduced the expression of the mcr A gene, showing that ANME archaea/methanogens might be the methane oxidizers for the N 2 O-AOM process. Our results implied that the N 2 O-AOM process was an overlooked process for synchronous control of methane and nitrous oxide and may contribute to the future management of greenhouse gases emissions from landfills.
Jie Ma,Linhui Lei,Zhiwei Gong,Zongping Wang,Hui Liu,Guanghao Chen,Gang Guo
The efficacy of in-situ bioremediation of chlorinated ethenes (CEs)-contaminated groundwater is heavily contingent upon the provision of exogenous electron donors to facilitate reductive dechlorination by dechlorinating bacteria. Nonetheless, methanogenic archaea have been reported to engender competition for the limited electron donor supply, thereby diminishing dechlorination efficiency. This study proposes a novel strategy to enhance reductive dechlorination by reducing the particle size of polyhydroxyalkanoate (PHA) to the micrometer scale, thereby inhibiting methanogenic competition for electron donors. The results demonstrate that trichloroethylene (TCE) biodegradation efficiency peaked at a PHA particle size of 500 μm, significantly surpassing the efficiency observed in groups with particle sizes of 50 and 2000 μm. Furthermore, the electron utilization efficiency of dechlorinating bacteria (represented by Geobacter , Dehalobacter , Anaerolinea , etc in this study) was as high as 94.82 % over methanogenic archaea (represented by Methanobacterium ) in the 500 μm group. Mechanistic analyses revealed that the 500 μm PHA particles activated dark oxygen, leading to the generation of reactive oxygen species that decreased the abundance of the methanogenic functional gene McrA and increased the abundance of dechlorinating functional gene TceA relative to the total microbial genome gene (in terms of 16S rRNA). In contrast, PHA particles of 50 μm exhibited lower TCE biodegradation efficiency due to particle aggregation, while particles of 2000 μm exhibited reduced efficiency due to lower specific surface area. This study moves a step for the in-situ microbial remediation of CEs-contaminated groundwater.
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