Isolation and Characterization of Paraquat-Degrading Extracellular Humus-Reducing Bacteria from Vegetable Field

The aim of this paper is to isolate pure cultures that are capable of degrading paraquat (PQ) anaerobically with humic substances (humus) as the sole electron acceptor. Three facultative anaerobic bacteria (PQ-1, PQ-2, and PQ-3) were successively isolated from vegetable soil in Sanya city, China, via enrichment procedure with PQ and anthraquinone-2,6-disulphonate (AQDS) under anaerobic conditions. Batch experiments were conducted to investigate isolates' PQ anaerobic degradation activity. Results showed that three strains were all capable of degrading PQ directly with AQDS as the sole electron acceptor (18.6% removal within 48h), and the microbial process might be AQDS dependent. The addition of low molecular weight organic substrate, such as sucrose, could enhance the anaerobic degradation of PQ from 18.6% to 34.2%, and the degradation rate reached 100% after 5-day incubation. This study was the first paper reporting that pure cultures have the ability to anaerobically degrade PQ with AQDS as the sole electron acceptor.