Investigation of the Biodegradation of 4 - CHL Chlorobenzoic Acid

Abstract

As part of our efforts in establishing bioremediation of a PCB metabolized dead end product, 4-Chlorobenzoic acid, we assessed the aerobic biodegradation of 4- Chlorobenzoic acid (4CBA) by three microorganisms viz. Pseudomonas aeruginosa MTCC 2297, Bacillus subtilis and Pleurotus ostreatus. The ability of these organisms to degrade 4CBA in liquid medium was improved by the use of continuous culture, repeated sequential subculturing and providing a combination of other carbon source. Each organism was observed to have different tolerance limit of the compound above which they could not grow. Tolerance limit in Bacillus subtilis was found to be 0.8 mg mL-1, Pseudomonas aeruginosa had higher tolerance limit of 4.8 mg mL-1, while it was found to be much higher, 10 mg mL-1, in Pleurotus ostreatus. P. aeruginosa effectively degraded 4CBA in concentrations of 3, 3.5, 4 and 4.5 mg mL-1 at a rate of 0.028, 0.037, 0.049 and 0.051 mg h-1 respectively, while B. subtilis degraded 4CBA in the concentrations of 0.2, 0.4, 0.6 and 0.8 mg mL-1 at a rate of 0.012, 0.027, 0.041 and 0.048 mg h-1 respectively. The metabolite obtained from the degradation was 4-Chlorocatecol (4CC), suggesting that the pathway involved in degradation is most likely to be Oxygenolytic Dehalogenation. The fungal stain showed a clear zone of disappearance of 4CBA on Potato Dextrose Agar plates till a concentration as high as 10 mg mL-1. Quantitative estimation of its degradation was not determined due to its prolonged incubation time.