Comparative Metagenomics To Study The Impact Of Methyl Parathion On Farmland Bacterial Populations

Methyl parathion is a broad-spectrum organophosphate insecticide and acaricide that has been classified as a Class I insecticide with restrictions for use by the U.S. Environmental Protection Agency. It is commonly applied as a dust, powder, concentrate, emulsion, or granules to inhibit boll weevils and other insects found in agricultural crops. Studies showed that methyl parathion (MP) is generally hydrolyzable and rapidly breaks down in water and sediments via photolysis and biodegradation by various microorganisms. This study uses metagenomics to compare the effect of MP on farmland soil microorganisms population. It was found that the unamended soil sample contained an abundant phylum of proteobacteria (45%) which are known to degrade MP. However, upon amending the soil with MP a net reduction of microbial species was observed, including in species harboring degradation biomarkers. Based on bioinformatics data collected from MG-RAST, the methyl parathion degradation (MPD) pathway is likely incomplete, effectively blocked with the formation of p-nitrophenol (PNP). PNP is also poisonous and significantly reduces bacterial metabolism and growth. p-nitrophenol genes are primarily found on mobile elements that were not present within these soil samples. It is therefore likely that upon inoculation into MP , the underlying bacterial population degraded MP to PNP but were unable to proceed further and slowly died off. The putative MPD species found for this study is the Rhizobium sp. MTP-10005, an alphaproteobacterium, since it is the one that has the biodegradation capability via the maleylacetate and hydroxyquinol of the methyl parathion degradation pathway.