Characterization of p-nitrophenol degrading actinomycetes from Hundung limestone deposits in Manipur, India

Abstract

p-Nitrophenol (PNP), a major nitroaromatic xenobiotic is released into the environment as a result of its widespread use and as a breakdown product of organophosphate (OP) agricultural pesticides such as parathion and methyl parathion. It is highly toxic to soil microflora and other non-target organisms. Of several Microbial Biotechnology Research Laboratory (MBRL) strains isolated from limestone deposits in Ukhrul, Manipur, India, two strains, (HS4-2 and HS6-1) were found to be promising PNP biodegraders, degrading up to 30 mg/L PNP in neutral basal salts medium (BSM, pH 7.0). Higher strength alkaline BSM (5X BSM, pH 8.0) was found to be more favorable for PNP degradation by these strains. Under these more optimal conditions, HS4-2 and HS6-1 could degrade up to 270 and 350 mg/L PNP respectively, remarkably high concentrations as PNP is quite toxic even at low concentrations. Only a few bacterial strains degrading such high concentrations of PNP have been reported. As these strains seem promising, they were subjected to phenotypic and genotypic characterization. The phenotypic characteristics of these strains were typical of actinomycetes. 16S recombinant deoxyribonucleic acid (rDNA) sequence analyses indicated strain HS6-1 to have the highest level of sequence similarity with Rhodococcus triatomae IMMIB RIV-085(T)/AJ854055 (98.28%) and HS4-2 with Brevibacterium casei NCDO2048 (T)/X76564 (99.37%). Strain HS6-1 may possibly be a novel species of Rhodococcus. Further studies on optimization, kinetics and pathways of biodegradation can improve the biodegrading capacities of these actinomycete strains.

Keywords: Nitroaromatics, p-nitrophenol, limestone deposits, Hundung, Brevibacterium, Rhodococcus