Biodegradation of 2-Chlorophenol by Rhodopseudomonas palustris

A phototrophic bacterial culture that assimilates 2-chlorophenol (2-CP) was enriched from effluents of paper and wood industry. The isolated bacterium was identified as Rhodopseudomonas palustris based on its morphological characteristics, biochemical reactions, and fatty acid methyl ester gas chromatography (FAME-GC) analysis. The bacterium R. palustris being photoheterotrophic in nutrition was also able to switch between phototropic, aerobic, and anaerobic modes of metabolism, as evidenced by modulation of the bacterial photopigments. The switching of anaerobic to aerobic metabolism was evidenced by the presence of catechol, a product of aerobic oxidation of 2-CP in the spent medium and the disappearance of photopigment-specific absorbance in the organism. R. palustris degraded about 97% of the supplemented 2-CP from the culture medium in 40 days along with production of an exo-polysaccharide, which probably provides protection from substrate toxicity and enhances its bioavailability. Thin-layer chromatography (TLC) and gas chromoatography–mass spectrometry (GC-MS) analysis of the R. palustris spent medium extracts indicated the presence of phenol. The GC-MS data also indicated that phenol is metabolized through an ortho-cleavage pathway. Further analysis of the R. palustris cell-free extracts for enzymes showed the presence of a chlorophenol dehalogenase (CD) and a chlorophenol nicotinamide adenine dinucleotide phosphate (NADPH)-oxidoreductase (CNOR) with respective specific activities of 0.114 and 0.26 μmol/min/mg, suggesting an initial reductive dechlorination step during 2-CP catabolism. The study thus highlights the important roles of phototrophic bacteria in the decontamination of environmental pollutants from the polluted sites.