Microbial Community Composition And Functional Genes In The Anaerobic Hydrocarbon-Degrading System

Petroleum reservoir is a classical anaerobic environment in which contained a great deal of petroleum hydrocarbon and kinds of microorganisms. The giant geological bioreactor existed anaerobic oil hydrocarbon-biodegradation generally. To further understand the molecular mechanism in the microbial physiological and ecological processes, the petroleum reservoir production water was studied in this thesis. The microbial community and crucial hydrocarbon-degrading functional genes were analyzed by molecular method. The anaerobic hydrocarbon-degrading system was constructed through the enrichment culture, and the functional microorganisms capable of degrading hydrocarbon and physiological and ecological processes were further studied by the chemical and molecular methods combined.The microbial community composition and the hydrocarbon-degrading functional genes in the oil reservoir production water were researched by the molecular biology method. The results indicated that the sequences affiliated withβ- andγ-Proteobacteria dominated the bacteria; the sequences affiliated with the phylum Euryarchaeota predominated the archaea. The genes encoding the alkylsuccinate synthase (assA), the benzylsuccinate synthase (bssA) and the 6-oxocyclohex-l-ene-l-carbonyl-CoA hydrolase(oah) were also detected in several oil fields. Further phylogenetic analyses of the 16S rRNA genes and crucial functional genes indicated that the community composition was consistent with the functional genes. These analyses demonstrated that there existed the variety of functional microorganisms capable of degrading petroleum hydrocarbon.Three distinct reducing enrichment cultures with the oil reservoir production water as the inoculum and amended with alkanes mixture (C15-C20) were established and incubated under anoxic condition to construct the anaerobic hydrocarbon-degrading system. Phylogenetic analyses based on 16S rRNA gene indicated that Actinobacteria and Euryarchaeota predominated the bacteria and archaea from the methanogenic enrichment, respectively; Nitrospira and Crenarchaeota prevailed in the sulfate-reducing enrichment culture; y-Proteobacteria dominated the bacteria retrieved from the nitrate-reducing enrichment and no archaea was detected. The results showed that the available electron acceptors had a strong influence on the microbial community composition. In addition, genes encoding the alkylsuccinate synthase (assA) and methyl coenzyme-M reductase (mcrA) were amplified from the methanogenic enrichment and the results suggested that fumarate addition was probably involved in the degradation of n-alkanes.Chemical analyses of the metabolites in the anaerobic hydrocarbon-degrading system indicated that degradation of n-alkanes was most pronounced under sulfate-reducing condition, followd by nitrate-reducing and then the methanogenic condition with different electron acceptors. The types of short-chain fatty acids were greatly variant under distinct reducing conditions. Formic acid, acetic acid, propionic acid and isobutyric acid were detected in nitrate-reducing enrichment; acetic acid and isobutyric acid were detected in methanogenic enrichment; no short-chain fatty acids were detected under sulfate-reducing condition. The produced methane under methanogenic condition was much more than that under the sulfate-reducing condtion. The results demonstrated that the electron acceptor types had a strong influence on the characteristics that microorganisms degraded alkanes.The microbial physiological and ecological processes in the petroleum reservoir production water and anaerobic degrading-hydrocarbon system were researched in the present study. The research expanded the knowledge of the anaerobic degrading-hydrocarbon microorganisms and functional genes diversity, obtained the crucial information of the characteristics that microorganisms degraded alkanes with different electron acceptors and provided theoretical support for the energy recovery via methanogenesis of residual oil, especially the regulation mechanism under the alkanes-degrading methanogenic processes.