Petroleum hydrocarbons consisting of complicated mixtures of non‐aqueous and hydrophobic components have raised a widespread environmental problem and influenced the subsurface microbial ecology. Three subsurface soil samples were collected at an oil field (Hebei, China) to investigate the microbial diversity patterns and their responds to different petroleum hydrocarbon contaminations by using 16S rRNA gene cloning analysis combined with multivariate statistical analysis. The results showed that bacterial clone libraries fell into 16 phylogenetic divisions and 184 operational taxonomic units. Gammaproteobacteria ubiquitously dominated in all samples, while the relative abundance was lowest in the sample with the highest total petroleum hydrocarbon concentration. Known petroleum degrading bacterial genera Alcanivorax, Stenotrophomonas, Pseudomonas, Pseudoxanthomonas, Sphingomonas, and Acidobacterium were abundantly observed, whereas their relative abundances differed greatly under a selection pressure by the complex hydrocarbons. For example, Alcanivorax spp. were the most abundant genera in polycyclic aromatic hydrocarbons and chlorinated hydrocarbons contaminated soils, while both Alcanivorax spp. and Stenotrophomonas spp. dominated in benzene, toluene, ethylbenzene, and xylenes contaminated soils. Additionally, a large fraction of bacterial clones were expectedly affiliated to some uncultured bacteria originated from several similar polluted ecosystems, and bacteria without certain petroleum degrading capacities. These observations indicated that microbial diversity, abundance and community were highly influenced by the concentrations of petroleum constituents in the contaminated soil ecosystems. Understanding the underlying factors that control the abundance of these heterotrophic microorganisms may be advantageous in the bioremediation of petroleum contaminated environments.
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