Rhizoremediation of hydrocarbon-contaminated soil by Paspalum vaginatum (Sw.) and its associated bacteria

A rhizoremediation study was carried out on hydrocarbon-contaminated soil with Paspalum vaginatum (Sw.), a stoloniferous, perennial grass of the family Poaceae found mainly in the subtropics and tropical regions of the world. The contaminated soil analyses indicated a decrease in the level of hydrocarbons present after phytoremediation. There was equally, a significant reduction in growth parameters of the plant such as plant height, leaf number, tiller number and total dry weighth, compared to the control. Anatomical studies of sections of the plants' stems did not reveal the presence of accumulated oil within the tissues but rather denatured internal parenchymal cells structure were observed. Bacteria capable of degrading hydrocarbons were isolated from the rhizosphere of the grass. The isolates include: Arthrobacter sp., Bacillus pumilus , Bacillus sphaericus and Serratia marcescens . Growth in mineral salts medium supplemented with 0.5% crude oil for 21 days resulted in 95.9%, 95.6%, 98.3% and 96.7% degradation of oil for Arthrobacter sp., B. pumilus, S. marcescens and B. sphaericus respectively. A soil microcosm set up with the consortium of the isolates resulted in 87.7% degradation of crude oil in 45 days. These results suggest that P. vaginatum and its associated microbes are good candidates for rhizoremediation of hydrocarbon polluted soils.