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

Abstract

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.

Endosulfan Degradation through Cipadessa Baccifera and Clausena Dentata

“…Therefore degradation by these materials may be attributed to microbial degradation which may be due to utilization of pesticide as carbon source by the microorganisms (Singh et al, 2003 andSharaf et al, 2006). But studies show that pesticide cause damage to the microorganisms (Olaitan and Abiodun 2011).…”

Elimination of Inhibitory Effects of Chlorpyrifos and Quinolphos on Radish and Green Gram Seed Germination by Bioremediation of Contaminated Soil: A Comparative Study

“…One of the major environmental trepidations with pesticides is their capacity to affect soil, because of their persistence and mobility in the soil (Walker, 2003). The effects of Chlorpyrifos and quinolphos on the germination of radish and green gram seeds were tested.…”

“…(Ansaruddin and Vijayalakshmi 2003). It has been reported that repeated application of chlorpyrifos to the soil did not result in the development of a microbial population with the enhanced ability to degrade the pesticide (Singh et al, 2003).…”

Mitigation of Wastewater-Borne Chlorpyrifos in Constructed Wetlands: the Role of Vegetation on Partitioning

“…The rate of chlorpyrifos degradation was low in acidic soils, but increased considerably with increasing soil pH (4.7-8.4). High pH not only helps to develop enhanced chlorpyrifos degradation, but is also required to maintain it over long periods [22]. In groundwater, the half-life of chlorpyrifos decreases from 49.9 d to 44.4 d when pH increased from 7 to 8.5 [23].…”

“…However, less than 2.5% of added chlorpyrifos is reported to mineralize in wetland microcosms [29]. The mineralization that occurs is mostly due to microbial metabolism, as chlorpyrifos is rapidly degraded and mineralized to CO 2 when the test soils are amended with enhanced microorganisms [22]. Further toxic assessments are needed to accurately determine the rate of ultimate chlorpyrifos mineralization in CWs.…”