Molecular Characterization of Chlorpyrifos Degrading Bacteria Isolated from Contaminated Dairy Farm Soils in Nakuru County, Kenya

Abstract

Chlorpyrifos [O, O-diethyl O-(3,5,6-trichloro-2-pyridinyl) phosphonothioate] is an organophosphate widely used as an insecticide against a broad spectrum of pests, including as an acaricide against ticks and mites. Due to environmental persistence and toxicity, it should be eliminated quickly from contaminated sites through biodegradation. Microbial bioremediation is one of the most viable ways of removing Chlorpyrifos (CP) from the environment. However, few studies have been conducted on the bacterial diversity that degrades Chlorpyrifos. The enrichment culture technique conducted in this study isolated chlorpyrifos degrading bacteria in soils from dairy farms in Nakuru County, Kenya. The growth response of the bacteria and degradation of Chlorpyrifos was monitored every five days using UV-VIS Spectrophotometer (600nm). Sequential soil and liquid culture enrichments led to the isolation of eighteen (MA1-MA18) bacterial chlorpyrifos degraders with DNA sequences homologous to members of the genera Pseudomonas, Stenotrophomonas, Bacillus, Alicaligenes, and Achromobacter. The efficacy of four (4) strains was further investigated using Gas Chromatography-Mass Spectrometry (GC-MS) analysis. The results showed that all four strains significantly degraded Chlorpyrifos in Minimum Salt Medium (MSM), Lysinibacillus sp.HBUM206408 (79.52%), Stenotrophomonas maltophilia (71.43%), Pseudomonas putida (73.32%), and Achromobacter insuavis (71.03%), producing 2-Hydroxy-3,5,6-trichloropyridine (TCP) as a metabolite in MSM as the only source of carbon. Therefore, these strains can be used for the bioremediation of Chlorpyrifos in contaminated soil. There is a need for further studies to determine the possible mechanisms and other metabolites of Chlorpyrifos degradation by the isolates obtained in the study. Besides, future studies should explore the efficacy and survival of the organisms in the contaminated environment.