Isolation and Characterization of Oil-Degrading Microorganisms for Bench-Scale Evaluations of Autochthonous Bioaugmentation for Soil Remediation

Autochthonous bioaugmentation (uses microorganisms indigenous to the target sites) is proposed as a promising remediation technique that can overcome ecological barriers which usually impede successful applications of conventional bioaugmentation remedy. This study aimed to select and characterize strains for bench-scale evaluations of autochthonous bioaugmentation for remediation for oil-contaminated soil. Twenty-one oil-degrading stains were isolated from contaminated soil in an oil refinery plant in China. Six strains with high oil-degradation efficiencies were chosen for further morphological and biochemical characterizations, and their biosurfactant production potentials were measured. All six strains were able to produce biosurfactant, and the strain with the highest oil-degradation efficiency had the highest biosurfactant production potential, indicating the important role that biosurfactant played in accelerating biodegradation. Then we prepared the bioaugmentation consortium by mixing equal proportions of these six strains. Microcosm experiments showed that, after 84 days of incubation, the residual oil concentration in bioaugmented microcosms decreased by 63.2 ± 20.1 % while the residual oil concentration in the control only decreased by 21.3 ± 5.2 %. Gas chromatography-mass spectrum analysis further corroborated that 84 days of bioaugmentation significantly reduced the total number of contaminants and changed contaminant composition (resulting in higher relative abundance of short-chain alkanes and lower relative abundance of long-chain alkanes). All of these evidence showed that autochthonous bioaugmentation was an effective remediation technology, and the microbial consortium we isolated was an excellent bioaugmentation agent for crude oil-contaminated site.