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Applied and Environmental Microbiology, September 2003, p. 5198-5206, Vol. 69, No. 9
0099-2240/03/$08.00+0     DOI: 10.1128/AEM.69.9.5198-5206.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

Effects of Soil pH on the Biodegradation of Chlorpyrifos and Isolation of a Chlorpyrifos-Degrading Bacterium

Brajesh K. Singh,1,2* Allan Walker,1 J. Alun W. Morgan,1 and Denis J. Wright2

Horticulture Research International, Wellesbourne, Warwick CV35 9EF,1 Department of Biological Sciences, Imperial College London, Silwood Park Campus, Ascot, Berkshire SL5 7PY, United Kingdom2

Received 10 April 2003/ Accepted 25 June 2003

We examined the role of microorganisms in the degradation of the organophosphate insecticide chlorpyrifos in soils from the United Kingdom and Australia. The kinetics of degradation in five United Kingdom soils varying in pH from 4.7 to 8.4 suggested that dissipation of chlorpyrifos was mediated by the cometabolic activities of the soil microorganisms. Repeated application of chlorpyrifos to these soils did not result in the development of a microbial population with an enhanced ability to degrade the pesticide. A robust bacterial population that utilized chlorpyrifos as a source of carbon was detected in an Australian soil. The enhanced ability to degrade chlorpyrifos in the Australian soil was successfully transferred to the five United Kingdom soils. Only soils with a pH of >=6.7 were able to maintain this degrading ability 90 days after inoculation. Transfer and proliferation of degrading microorganisms from the Australian soil to the United Kingdom soils was monitored by molecular fingerprinting of bacterial 16S rRNA genes by PCR-denaturing gradient gel electrophoresis (DGGE). Two bands were found to be associated with enhanced degradation of chlorpyrifos. Band 1 had sequence similarity to enterics and their relatives, while band 2 had sequence similarity to strains of Pseudomonas. Liquid enrichment culture using the Australian soil as the source of the inoculum led to the isolation of a chlorpyrifos-degrading bacterium. This strain had a 16S rRNA gene with a sequence identical to that of band 1 in the DGGE profile of the Australian soil. DNA probing indicated that genes similar to known organophosphate-degrading (opd) genes were present in the United Kingdom soils. However, no DNA hybridization signal was detected for the Australian soil or the isolated degrader. This indicates that unrelated genes were present in both the Australian soil and the chlorpyrifos-degrading isolate. These results are consistent with our observations that degradation of chlorpyrifos in these systems was unusual, as it was growth linked and involved complete mineralization. As the 16S rRNA gene of the isolate matched a visible DGGE band from the Australian soil, the isolate is likely to be both prominent and involved in the degradation of chlorpyrifos in this soil.

* Corresponding author. Present address: Environmental Science, Macaulay Land Use Research Institute, Craigiebuckler, Aberdeen AB15 8QH, United Kingdom. Phone: (44)-1224-498200. Fax: (44)-1224-498207. E-mail: b.singh{at}macaulay.ac.uk.

Applied and Environmental Microbiology, September 2003, p. 5198-5206, Vol. 69, No. 9
0099-2240/03/$08.00+0     DOI: 10.1128/AEM.69.9.5198-5206.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Morgan, J. A. W., Bending, G. D., White, P. J. (2005). Biological costs and benefits to plant-microbe interactions in the rhizosphere. J Exp Bot 56: 1729-1739 [Abstract] [Full Text]  
  • Cho, C. M.-H., Mulchandani, A., Chen, W. (2004). Altering the Substrate Specificity of Organophosphorus Hydrolase for Enhanced Hydrolysis of Chlorpyrifos. Appl. Environ. Microbiol. 70: 4681-4685 [Abstract] [Full Text]  
  • Singh, B. K., Walker, A., Morgan, J. A. W., Wright, D. J. (2004). Biodegradation of Chlorpyrifos by Enterobacter Strain B-14 and Its Use in Bioremediation of Contaminated Soils. Appl. Environ. Microbiol. 70: 4855-4863 [Abstract] [Full Text]  


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