The bio-mitigation of acetochlor in soil using Rhodopseudomonas capsulata in effluent after wastewater treatment

Abstract

The bio-mitigation of acetochlor and improvement of fertility in soil using Rhodopseudomonas capsulata (R. capsulata) in effluent was investigated in this research. Acetochlor content and cytochrome P450 monooxygenase activity were tested using the HPLC method. EthB gene regulation was measured by RT-PCR. It was observed that acetochlor was not degraded under the control group. The addition of effluent containing R. capsulata and residual organics degraded acetochlor efficiently and re-mediated soil fertility. Acetochlor mitigation reached 100% after 5 days under the optimal group (2000 mg/L). Interestingly, the acetochlor began to be degraded after day 1 of inoculation. Further research indicated that EthB gene was expressed after the first day of inoculation. Subsequently, the cytochrome P450 monooxygenase was synthesized to degrade acetochlor under EthB gene regulation. Analysis revealed that EthB and cytochrome P450 monooxygenase were inducible gene expressions and enzyme. The acetochlor as stimulus signal induced EthB expression through signal transduction pathway. This process took 1 day for R. capsulata, as they were ancient bacteria. However, the organics in soil and the control group were deficient, which could not maintain R. capsulata growth for over 1 day. The residual organics in effluent provided sufficient carbon sources and energy for R. capsulata under four effluent groups. The new method completed the remediation of acetochlor pollution and the improvement of soil fertility and soybean processing wastewater treatment simultaneously, as well as realizing the resource reutilization of wastewater and R. capsulata as sludge.