Comparison of in-situ biodegrading abilities of Pseudomonas putida mutants: leuB− auxotroph, fliC− non-motility, and cheA− non-chemotaxis

Bioremediation of pollutants in natural environments is affected by many factors, such as bacterial survival, motility, and chemotaxis. However, these roles in in-situ biodegradation of organophosphorus pesticides have not been examined extensively. In this paper, a highly effective methyl-parathion (MP) degrading strain, Pseudomonas putida DLL-1, which also demonstrates motile ability and chemotactic response toward MP, was selected as the research material. A leuB− auxotroph mutant A3-27 and fliC− non-motility mutant a4-8 were first constructed by random insertion of the kanamycin gene into the chromosome of P. putida DLL-1 with the mini-transposon system. Biodegradation of MP in liquid medium and soil microcosms by A3-27, a4-8 and a previously constructed cheA− non-chemotaxis mutant P. putida DAK were compared. The kinetic parameters for MP degradation were all similar in the well-mixed liquid systems. However, in soil microcosms, all the three mutants had lower degrading rates compared with wild-type P. putida DLL-1. The auxotroph mutant A3-27 had the lowest degrading rate and could only degrade 25.7–34.2% MP in 5 days, and the non-motility mutant a4-8 and non-chemotaxis mutant DAK could only degrade 53.5–68.1% and 64.3–85.7% MP, respectively. This paper emphasizes, for the first time, the use of non-auxotroph bacteria for efficient removal of organophosphorus pesticides in contaminated sites, and also points out the importance of select microorganisms with specific motile or chemotactic affinities in optimizing pesticide bioremediation.