Carbamate Pesticides and Their Biological Degradation: Prospects for Enzymatic Bioremediation

Biochemistry of Microbial Degradation of Hexachlorocyclohexane and Prospects for Bioremediation

“…Multiple systems have been reported for several other pesticides and toxins. For example, at least three and often more have been described for organophosphates, carbamates, glyphosate, triazines, 2,4,6-trinitrotoluene, and even other organochlorines like endosulfan and trichloroethylene (3,28,81,154,156,157,164,188; C. J. Hartley, S. J. Dorrian, L. J. Briggs, M. R. Williams, R. J. Russell, and J. G. Oakeshott, international patent application PCT/Au2007/000640). This unusual feature of the lin system may reflect the relative recalcitrance of HCH to degradation, as is also suggested by the length of the lin pathway.…”

“…The first detoxification step in other xenobiotic catabolic systems, for example, the Oph/OpdA organophosphate-degrading enzyme, approach diffusion-limited kinetics (194), and some of those for glyphosate, carbamates, and atrazine also have specificity constants in excess of 10 4 s Ϫ1 M Ϫ1 (28,154). However, the specificity constants of LinB for its preferred HCH isomer are nearly 3 orders of magnitude lower, and the specificity constant of LinA has not been estimated at this time.…”

“…The technology does depend on a liquid, or at least very moist, environment to allow the enzyme access to the substrate. Nevertheless, enzymatic bioremediants are now commercially available for the cleanup of certain pesticides in large-scale liquid wastes (1,15,28,154) and show promise for the treatment of various stockpiles, soils, and, in some cases, external surfaces of commodities (22,35). The good results for the enzymatic treatment of stockpiles are of particular interest with respect to very concentrated HCH deposits like dump sites, where microbial growth is severely limited by the availability of nutrients.…”

Heterologous expression of the methyl carbamate-degrading hydrolase MCD

“…Although MCD is almost certainly the current best candidate for a free-enzyme pesticide bioremediant for carbamate insecticides, it is considerably slower than the high benchmark rate set by the only commercially produced free-enzyme bioremediant, OpdA (Horne et al, 2002;Scott et al, 2008), which has a k cat /K m for some substrates of nearly 10 8 s −1 M −1 (Jackson et al, 2005). It should be possible to increase substantially the rate at which MCD operates by in vitro evolution, not least because there is a facile plate assay for high throughput screening of libraries of mutant MCDs for enhanced hydrolysis (Cheesman et al, 2007). Moreover, we have previously improved the phosphotriestease, OpdA, and atrazine dechlorinase, AtzA, to enhance their suitability as free-enzyme bioremediants using similar methods Scott et al, 2009).…”

“…The environmental fate of the carbamates depends to a significant degree on their metabolism by soil microflora (Cheesman et al, 2007) and three enzymes that may contribute to this metabolism have been identified. CahA (Hayatsu et al, 2001;Hashimoto et al, 2006) and CehA (Bornscheuer, 2002), isolated from an Arthrobacter sp.…”