2.8.2 Hydrolases
Another group of enzymes commonly used in pesticide bioremediation is hydrolases
(Zhongli et al. 2001). The presence of hydrolysable groups in a pesticide or
xenobiotic molecule is an important factor in determining its anaerobic biodegradability. Hydrolases catalyze the hydrolysis of many major biochemical classes of
pesticides (esters, peptide bonds, carbon–halide bonds, ureas, thiosters, etc.) and
generally function in the absence of redox cofactors (Scott et al. 2008). Esterases are
enzymes that catalyze the hydrolysis of carboxylic esters (carboxyestrases), amides
(amidases), phosphate esters (phosphatases), etc. (Bansal 2012). Many insecticides
(organophosphates, carbamates, and pyrethroids) contain the carboxylic ester component, and the enzymes that can hydrolyze this type of ester bond are called
carboxyl-esterases. In this group, phosphotriesterases (PTEs) are one of the most
important classes (Chino-Flores et al. 2012). The first phosphotriestrase was isolated
from Pseudomonas aeruginosa strain MG, and this enzyme showed high catalytic
action against organophosphate pesticides. PTEs are encoded by genes called opd
(organophosphate-degrading), and the opd genes were first characterized in
Flavobacterium strain ATCC 27551 (Latifi et al. 2012). These enzymes distinctively
hydrolyzed phosphorus bonds such as P-O, P-F, P-NC, and P-S, and the hydrolysis
mechanism involved a water molecule at the phosphorus center. This enzyme
showed its potential to eliminate organophosphorus pesticide-contaminated environments (Ortiz-Hernandez et al. 2003).
Microbial degradation of organophosphorus compounds by hydrolysis of P-Oalkyl and P-O-aryl bonds is considered to be the most important step in detoxification (Sogorb and Vilanova 2002). Analogous phosphor-monoesterase and
diesterase, which degraded methyl and dimethyl phosphate, respectively, have
been reported in Klebsiella aerogenes (Wolfenden and Spence 1967). Organophosphorus hydrolase (OPH) and organophosphorus acid anhydrolase (OPAA) are one
of the most widely studied organophosphorus degrading enzymes (Mulbry and
Karns 1989; Singh et al. 1999). In bacterial enzymes, OPH from P. diminuta has a
wide range of substrate specificity (Manavathi et al. 2005). The highly active OPAA
molecule from Alteromonas undina is composed of a single polypeptide with a
molecular weight of 53 kDa (Cheng et al. 1993). However, another OPAA was
isolated from Alteromonas spp. JD6.5 is composed of 517 amino acids with a
molecular weight of 60 kDa and has been reported to play an important role in
cellular dipeptide metabolism (DeFrank and White 2002).
Other structurally and functionally distinct organophosphorus degradation
enzymes were three unique parathion hydrolases, which were characterized from
Gram-negative bacterial isolates. An exclusive phosphotriesterase has been characterized from Nocardioides simplex NRRL B-24074. Another novel
phosphotriesterase HOCA (Hydrolysis of Caroxone) was isolated from
P. monteilii (Horne et al. 2002a, b). This enzyme is required by the host for
phosphate metabolism and was suggested to originate from phosphodi- or
monoesterase. The enzyme phosphonatase was found capable to degrade
2 Bioremediation of Pesticides: An Eco-Friendly Approach for Environment. . .
51
Another group of enzymes commonly used in pesticide bioremediation is hydrolases
(Zhongli et al. 2001). The presence of hydrolysable groups in a pesticide or
xenobiotic molecule is an important factor in determining its anaerobic biodegradability. Hydrolases catalyze the hydrolysis of many major biochemical classes of
pesticides (esters, peptide bonds, carbon–halide bonds, ureas, thiosters, etc.) and
generally function in the absence of redox cofactors (Scott et al. 2008). Esterases are
enzymes that catalyze the hydrolysis of carboxylic esters (carboxyestrases), amides
(amidases), phosphate esters (phosphatases), etc. (Bansal 2012). Many insecticides
(organophosphates, carbamates, and pyrethroids) contain the carboxylic ester component, and the enzymes that can hydrolyze this type of ester bond are called
carboxyl-esterases. In this group, phosphotriesterases (PTEs) are one of the most
important classes (Chino-Flores et al. 2012). The first phosphotriestrase was isolated
from Pseudomonas aeruginosa strain MG, and this enzyme showed high catalytic
action against organophosphate pesticides. PTEs are encoded by genes called opd
(organophosphate-degrading), and the opd genes were first characterized in
Flavobacterium strain ATCC 27551 (Latifi et al. 2012). These enzymes distinctively
hydrolyzed phosphorus bonds such as P-O, P-F, P-NC, and P-S, and the hydrolysis
mechanism involved a water molecule at the phosphorus center. This enzyme
showed its potential to eliminate organophosphorus pesticide-contaminated environments (Ortiz-Hernandez et al. 2003).
Microbial degradation of organophosphorus compounds by hydrolysis of P-Oalkyl and P-O-aryl bonds is considered to be the most important step in detoxification (Sogorb and Vilanova 2002). Analogous phosphor-monoesterase and
diesterase, which degraded methyl and dimethyl phosphate, respectively, have
been reported in Klebsiella aerogenes (Wolfenden and Spence 1967). Organophosphorus hydrolase (OPH) and organophosphorus acid anhydrolase (OPAA) are one
of the most widely studied organophosphorus degrading enzymes (Mulbry and
Karns 1989; Singh et al. 1999). In bacterial enzymes, OPH from P. diminuta has a
wide range of substrate specificity (Manavathi et al. 2005). The highly active OPAA
molecule from Alteromonas undina is composed of a single polypeptide with a
molecular weight of 53 kDa (Cheng et al. 1993). However, another OPAA was
isolated from Alteromonas spp. JD6.5 is composed of 517 amino acids with a
molecular weight of 60 kDa and has been reported to play an important role in
cellular dipeptide metabolism (DeFrank and White 2002).
Other structurally and functionally distinct organophosphorus degradation
enzymes were three unique parathion hydrolases, which were characterized from
Gram-negative bacterial isolates. An exclusive phosphotriesterase has been characterized from Nocardioides simplex NRRL B-24074. Another novel
phosphotriesterase HOCA (Hydrolysis of Caroxone) was isolated from
P. monteilii (Horne et al. 2002a, b). This enzyme is required by the host for
phosphate metabolism and was suggested to originate from phosphodi- or
monoesterase. The enzyme phosphonatase was found capable to degrade
2 Bioremediation of Pesticides: An Eco-Friendly Approach for Environment. . .
51