Isolation, Characterization And Mineralizing Mechanism Of Degradative Strains For Cypermethrin

Cypermethrin is one of the most widely used synthetic pyrethriod insecticide. The contamination to the environment has aroused most of the public concern. There were many studies conducted on the microbial remediation of pesticide, and most of them focused on the isolation, characterization, degrading abilities of pesticide-degrading strains. But several microorganisms which could degrade cypermethrin have been reported.In this study, we isolated three cypermethrin-degrading strains by enrichment culture and screening, found that all of them could use cypermethrin as the carbon source. Then we studied the cypermethrin-degrading strains, including their characterization, growth, degrading abilities, metabolites analysis and the relationship between the degrading ability and cell surface hydrophobicity. The main results are as follows:1 From the activated sludge samples obtained from pesticide company, three cypermethrin-degrading bacterial strains were isolated and named in L12, L31 and L13. Then based on the results of morphology, physio-biochemical characteristics, constituents of fatty acid, G+C mol% and 16S rDNA analysis, the isolates were identified as Bacillus cereus L12, Exiguobacterium acetylicum L31 and Klebsiella pneumoniae L13. The GenBank accession numbers are HQ398861,JF950035,HQ398862, respectively.2 The growth and degrading abilities of each strain was tested by UV-Vis and GC-ECD. As a result, the strains L12 and L31 have higher degrading abilities than the strain L13. Strain L12 could degrade 68% and 86% of cypermethrin (50mg/L) within 2 days and 5 days. Strain L31 could eliminate 75% and 83% of cypermethrin (50mg/L) within 3 days and 5 days, respectively. However, strain L13 only could use 66% of cypermethrin (50mg/L) in 5 days as carbon source.3 The main metabolite of cypermethrin (3-PBA) was analysed by TLC and HPLC. This indicated that all of the three strains could synthesis carboxylesterase, which can break the carboxylic ester bond of cypermethrin specificly into 3-PBA and DV chrysanthemic acid. Then according to the recent studies, we supposed that the metabolite 3-PBA would further degrade into phenol and brenzcatechin.4 During the growth of the three strains and the cypermethrin degradation, the cell surface hydrophobicity (CSH) of each strain was tested by MATH. And the results showed that strain L12 and L31 not only had higher CSH but also had stronger degrading abilities than strain L13. These suggested that CSH might influent the degrading abilities of the cypermethrin-degrading strains, there was a relationship between high CSH and strong degrading ability.