Interactions of rice (Oryza sativa L.) and PAH-degrading bacteria (Acinetobacter sp.) on enhanced dissipation of spiked phenanthrene and pyrene in waterlogged soil

The effects of cultivation of rice (Oryza sativa L.) and PAH-degrading bacteria (Acinetobacter sp.) separately, and in combination, on the dissipation of spiked phenanthrene and pyrene (0, 50 + 50, 100 + 100, 200 + 200 mg kg⁻¹) in waterlogged soil were studied using pot trials. The population of introduced PAH-degrading bacteria remained at 10⁵ CFU g⁻¹ dry soil after 20 days of treatment with Acinetobacter sp. only, but increased to 10⁶ when planted with rice simultaneously. Shoot and root biomass of rice when grown alone was adversely affected by spiked PAHs, but significantly increased by 2–55% and 8–409%, respectively, when inoculated with Acinetobacter sp.. Phenanthrene and pyrene concentrations in roots ranged from 1–27 and 20–98 mg kg⁻¹, respectively, while their concentrations in shoots were generally lower than 0.2 mg kg⁻¹. The dissipation of phenanthrene was mainly due to abiotic loss as 70–78% phenanthrene was lost from the control soil at the end of 80 days, while removal of 86–87% phenanthrene had been achieved after 40 days in the treatment co-cultivated with Acinetobacter sp. and rice. Compared with the control where only 6–15% of pyrene was removed from soil, a much higher dissipation of pyrene (43–62%) was attained for the treatments co-cultivated with Acinetobacter sp. and rice at the end of 80 days. The results demonstrated that co-cultivation of rice and PAH-degrading bacteria may have a great potential to accelerate the bioremediation process of PAH-contaminated soil under waterlogged conditions. Copyright © 2006 Elsevier B.V. All rights reserved.