Submitted to: Microbiological Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 29, 2000
Publication Date: N/A
Interpretive Summary: Organophosphate pesticides such as coumaphos and chlorfenvinphos are used throughout the world to control ticks on cattle. In the U.S., coumaphos is used by the USDA in a program designed to prevent the re-introduction of cattle fever through ticks imported from Mexico. This program employs a series of dipping vats placed at border crossing points in Mexico as well as vats on the U.S. side of the border. Although evaporation pits and waste lagoons were used for many years to dispose of coumaphos-containing dip wastes, the USDA recently adopted the use of a biofilter system to detoxify these dip wastes. In this study, scientists characterized an unusual enzyme that breaks down coumaphos. An understanding of this enzyme and the responsible gene will aid in the isolation of other useful pesticide degrading organisms and will lead to the development of better waste disposal technologies.
We characterized a novel organophosphorus hydrolase (OPH) activity expressed by Nocardiodes simplex NRRL B-24074, a member of a coumaphos-degrading microbial consortium from cattle dip waste. Like the previously characterized OPH from Nocardia sp. strain B-1 (NRRL B-16944), OPH activity in N. simplex is located in the cytoplasm and is expressed constitutively. The purified enzyme is monomeric, has a native molecular size of 45,000 d, and has a specific activity toward ethyl parathion of 33 umole/min-mg protein. Km constants for the enzyme with the structurally related organophosphate pesticides ethyl parathion and EPN were 100 uM and 345 uM, respectively. Although OPH activity in extracts did not require the addition of divalent cations, the purified enzyme lost activity during dialysis against phosphate buffer and this activity could be restored after incubation in buffer containing either cobalt sulfate or copper sulfate. Our results suggest that OPH activity in N. simplex is distinct from other known OPHs and that the responsible gene is unrelated to known genes.