Bacterial Assisted Phytoremediation of Crude Oil-Contaminated Soil

Abstract

Petroleum hydrocarbons are recalcitrant compounds and their adverse environmental and public health effects demand that efficient and eco-friendly remediation technologies be devised as countermeasures. The synergistic use of plants and bacteria is considered as one of the efficient technologies for the restoration of crude oil-contaminated soil. The studies performed in this thesis were aimed to (ⅰ) isolate and characterize bacteria associated with the plants growing well in crude oil-contaminated soil, (ⅱ) study the effect of augmentation of hydrocarbon-degrading bacteria on plant growth and crude oil degradation in vitro and in vivo. A large number of hydrocarbon degrading bacteria were isolated from the rhizospheric soil, root and shoot interior of grasses (Lolium perenne, Leptochloa fusca, Brachiaria mutica) and trees (Leucaena leucocephala and Acacia ampliceps) vegetated in crude oil-contaminated soil. The rhizospheric soil yielded 22 (59.45%), root interior yielded 9 (24.32%) and shoot interior yielded 6 (16.21%) hydrocarbon-degrading bacteria. These bacteria possessed genes encoding alkane hydroxylase and showed multiple plant growth-promoting activities. Bacillus (48.64%) and Acinetobacter (18.91%) were dominant genera found in this study. Green house studies revealed that augmentation with crude oil-degrading bacteria enhanced plant growth and crude oil degradation. Colonization and metabolic activity of the endophytes were higher in the rhizosphere and endosphere of B. mutica than L. fusca. The plant species affected not only colonization pattern and biofilm formation of the inoculated bacteria in the rhizosphere and endosphere of the host plant, but also affected the expression of alkane hydroxylase gene, alkB. The beneficial plant-bacteria partnership was applied in the vicinity of an oil exploration and production company for the remediation of crude oil-contaminated soil. Bacterial augmentation improved plant growth, enhanced crude oil degradation, and reduced soil toxicity and these were significantly (p < 0.05) higher than those where plants or bacteria were used individually. A positive relationship (r = 0.70) observed xiv between alkB gene expression and crude oil reduction indicates that expression of catabolic gene (alkB) is important for hydrocarbon mineralization. On the basis of in vitro and in vivo studies, it is concluded that for practical application, support of potential bacteria combined with the grasses is more effective approach than the use of plants and bacteria individually. This technology can be applied for effective remediation of crude oil-polluted sites.