Wednesday, November 15, 2006

Degradation of Fenamiphos, EPTC and Butylate by Two Strains of Rhodococcus sp. B30 Isolated from an EPTC Enhanced Soil.

Chijioke Joshua, Egbe Egiebor, Ramble Ankumah, and John P. Davidson. Tuskegee University, Milbank Hall, Tuskegee, AL 36088

Enhanced degradation results in a rapid increase in the degradation rate of a pesticide with repeated application to the same soil, as compared with their degradation rate in soil not previously exposed to the pesticide. Some soils which have been enhanced to degrade one pesticide have also been reported to rapidly degrade other pesticides in the same or other classes. This phenomenon is called cross-enhancement (adaptation) of pesticide degradation and has been observed to occur among thiocarbamates and organophosphates, although the evidence is still being investigated. Even though the mechanism of enhanced degradation is not fully known, most researchers have attributed it to microbial adaptation.  One group of microorganisms which has been observed to possess the capability to rapidly degrade thiocarmamate herbicides are the Rhodococcus species. The objective of this study was to determine the capability of pure cultures of two new strains of Rhodococcus sp. (B30E and B30F) obtained from repeated culturing in sub-limiting EPTC medium to utilize three pesticides, butylate and EPTC (thiocarbamates) and fenamiphos (organophosphate) as sole carbon sources, respectively. This study was conducted by inoculating the strains into minimal salt media supplemented with the pesticides and subsequently measuring the growth using plate counts and optical density at 600 nm (OD600). The results of this study revealed that both new strains were capable of utilizing the each pesticide as sole carbon and nitrogen sources at a similar rate.  In each case growth of both strain B30E and B30F on EPTC seemed to be slightly better than on the other pesticides. The similar growth rate of Rhodococcus sp. strains B30E and B30F on these different classes of pesticide, suggests that soil bacteria involved in enhanced degradation may also be capable of rapidly degrading different classes of pesticides applied to the same field.