Mycoremediation and Environmental Sustainability by Ram Prasad

Author:Ram Prasad
Language: eng
Format: epub
Publisher: Springer International Publishing, Cham

7.5 Degradation of Insecticides

7.5.1 Degradation of Organophosphate

The biodegradation of organophosphorus insecticides (OPs) has been studied in soils and in bacterial cultures (Benning et al. 1994; Lai et al. 1994). Less attention has been given to the metabolic removal of these compounds by fungi in general and WRF in particular especially considering the catalytic efficiencies of LMEs . P. chrysosporium is the most studied WRF proving its ability to degrade a variety of pesticides. The fungus has been demonstrated to mineralize 12.2–27.5% of 14C-radiolabeled chlorpyrifos, fonofos and terbufos to CO2, which has been attributed to LMEs. Proposed pathway for degradation of chlorpyrifos is given in Fig. 7.3. Hernandez et al. (1998) demonstrated that chloroperoxidase from the fungus Caldariomyces fumago was able to oxidize seven of ten OPs assayed, although no oxidation was detected when other heme proteins such as lignin peroxidase, horseradish peroxidase or cytochrome c were used. On the other hand, a fungal laccase produced by Pleurotus ostreatus has been reported as able to perform the oxidative degradation of two OP nerve agents, VX and RVX, with a mediator-assisted reaction. Hydrolytic cleavage of fenitrothion and fenitrooxon by the non-ligninolytic fungi showed that OP degradation by fungi was not necessarily by LMEs , rather by many other metabolic pathways (Baarschers and Heitland 1986). WRF including Coriolopsis polyzona, P. chrysosporium, P. ostreatus and T. versicolor are known to cause significant removal of pesticides (as measured by substrate disappearance) in vivo (Pointing 2001). These suggest that the ability to degrade OP insecticides may be widespread or at least relatively common among the fungi, though the metabolic system varies.

Fig. 7.3Proposed pathway degradation of chlorpyrifos (Modified from Chen et al. 2012). Abbreviation: TCP 3,5,6-trichloro-2-pyridinol and DETP diethylthiophosphoric acid

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