Abstract
Pseudomonas aeruginosa and Pseudomonas mendocina degrading malathion were studied. Morphological, biochemical and 16S rRNA genes for bacterial identification were selected. Biodegradation of some organophosphorus compounds with the 2 bacterial isolates was determined by high performance liquid chromatography (HPLC). P. aeruginosa strain completely removed diazinon, malathion and fenitrothion, but not chlorpyrifos within 14 days. P. mendocina strain was not able to degrade malathion, diazinon and chlorpyrifos completely and no significant degradation for chlorpyrifos. The bacterial growth curve showed a steady increase in the two bacterial isolates masses during malathion degradation. The highest growth rates were with yeast extract, glucose and citrate for the 2 isolates, but not with phenol. Shaked high inoculum density with incubation at 30°C of malathion bacterial cultures were found to be the optimum conditions for malathion degradation. Bacterial culture extracts subjected to liquid chromatography/mass spectrometry (LC/MS) analysis revealed that the separated products were malathion monocarboxylic acid and malathion dicarboxylic acid. Molecular characterization of carboxylesterase enzyme revealed that carboxylesterase amino acid sequences of the 2 isolates showed high identity to other carboxylesterase enzymes of P. aeruginosa and P. mendocina, respectively. Phylogenetic analysis showed that P. aeruginosa was localized in a separate branch from other carboxylesterase producing Pseudomonas sp. So, it is suggested that this enzyme is a novel esterase enzyme. Use of pesticide-degrading microbial systems for removal of organophosphorus compounds from the contaminated sites requires an understanding of ecological requirements of degrading strains. The results provided an important insight into determining the bioremediation potential of both strains. But the mentioned bacteria cannot be the aim of bioremediation due to risk of public health hazard, hence these bacteria cannot be used in bioremediation but their purified enzymes could. Key words: Biodegradation, carboxylestrase, organopgosphorus pesticides, Pseudomonas aeruginosa, Pseudomonas mendocina.
Highlights
Organophosphorus compounds (OPCs) have been used worldwide as plasticizers, petroleum additives and as pesticides since the Second World War
Bacterial culture extracts subjected to liquid chromatography/mass spectrometry (LC/MS) analysis revealed that the separated products were malathion monocarboxylic acid and malathion dicarboxylic acid
A total of 18 bacterial isolates were recovered from thirtysix domestic sewage, agricultural wastewater and soil samples collected from different sites in Beni-Suef City, Egypt
Summary
Organophosphorus compounds (OPCs) have been used worldwide as plasticizers, petroleum additives and as pesticides since the Second World War. OPCs are biodegradable, they are highly toxic to mammals and other non-target animals (Ragnarsdottir, 2000). Organophosphorus compounds inhibit the acetylcholinestrase resulting in the over-stimulation of acetylcholine receptors in the synapses Overstimulation of acetylcholine receptors at the cholinergic synapses of autonomic, central nervous systems and neuromuscular junctions causes agitation, hypersalivation, confusion, convulsion, respiratory failure and death (Eddleston et al, 2008)
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