Studies on the degradation of chlorinated phenolic compounds by Pseudomonas spp.

Abstract

Chlorinated aromatic compounds used as herbicides, pesticides, preservative . solvent . and lubricants constitute a major class of environmental pollutants. The degradation of many chlorinated aromatics in the environment has been found to be facilitated by bacteria. The present study was conducted to explore the potential of new microbial strains (bacteria and fungi) for the biodegradation and biotransformation studies of chlorinated phenols. Chlorinated phenol degrading bacteria were isolated from a chlorophenol contaminated site. Initially 20 isolates having the ability to utilize Pentachlorophenol (PCP : 10 ppm) were screened and six were selected on the basis of best growth, When these isolates were characterized morphologically and biochemically, they were found to be Pseudomonas sp. All these bacterial strains along with two other strains P. putida RE 20-t. and P. putida F 1 were checked for their growth and tolerance limits on different concentrations (50-500 ppm) of chlorinated phenols on nutrient agar and mineral salt media (PNR) with and without glucose. · On nutrient agar plates containing 2-Chlorophenol (2-CP) rich growth was observed upto the maximum concentration of 400 ppm while ?n PNR-G agar plates rich growth was observed at a maximum concentration of 3 50 ppm and on P. R agar plates bacterial strains showed the best growth at 100 ppm. With 4-Chlorophenol (4-CP) rich growth was seen upto the maximum concentration of 300, 100 and 50 ppm on nutrient agar, PNR-G and PNR agar plates. 2,4-Dichlorophenol (2,4-DCP) showed the maximum tolerance upto the concentration of 300 ppm. In mineral media containing glucose and 2 4- DCP rich growth was observed upto 300 ppm only by CP-1while when 2.4-DCP was ' supplied as the sole source of carbon and energy rich growth was show n upto a concentration of 150 ppm. With 2,5-Dichlorophenol (2,5-DCP) on nutrient agar plates rich growth was observed upto 200 ppm and on PNR-G maximum growth tolerance was observed at 150 ppm and about all the bacterial strains showed growth on 2.5-DCP as a sole source of 100 ppm. 2.6- Dichlorophenol (2,6-DCP) showed rich growth upto 300 ppm. In this case low level of growth was observed at 400 ppm. While on P. R-G agar plates bacterial strain CP-1 showd a rich growth at a concentration of 150 ppm. On P1 TR with and without glucose rich growth was observed upto 150 and 100 ppm. So all the three isomers of dichlorophenols showed nearly the same pattern of growth tolerance. In case of

Pentachlorophenol (PCP) rich growth was observed upto 300 ppm on nutrient agar plates. 200 ppm on PNR-G and 100 ppm on PNR agar plates. Further one bacterial strain identified as Pseudomonas aeruginosa CP-1 was selected and characterized for growth and biotransformation studies. Optimum pH and temperature for growth was found to be 7.5 and 25 °C respectively. Shake flask transformation of 2-CP with growing cell condition showed the maximum degradation of 50 % of 300 ppm initial concentration while with 4-CP 22.9 % reduction was observed on sixth day of incubation. 2,6-DCP showed maximum reduction of 27.01 % upto the maximum concentration of 150 ppm respectively. With induced and uninduced washed cell suspension maximum reduction was observed with uninduced washed cells with all the chlorinated phenols. So with growing cell condition the cell mass increased while concentration of the chlorinated phenols decreased with the passage of time while induced and uninduced washed cell suspension indicated that induction had not much effect on the degradative ability of Pseudomonas aeruginosa CP-1.

In the present study five fungal strains (FCP1-FCP5) capable to assimilate Pentachlorophenol were isolated from soil. The isolated strains were identified as Aspergillus niger, Penicillium islandius, Bjerkandera adusta, Aspergillus terreus and Cephalosporium curtipes. Three of the five fungal isolates; FCPI, FCP2 and FCP3 showed best growth with pentachlorophenol as well as with 2-chlorophenol; 2-chlorophenol: 2.4- dichlorophenol; 2,5-dichlorophenol and 2,6-dichlorophenol on agar media. None of the ' fungal isolate utilized any of the chlorophenol as sole source of carbon and energy. When ' fungal strains were adopted to higher concentrations of chlorinated phenols, they show ed good growth on concentrations of PCP up to 60 ppm, with 2-, and 4-chlorophenol up to 70 ppm, with 2,5- and 2,6-dichlorophenol up to 50 ppm and with 2,4-dichlorophenol up to 30 ppm in mineral salt agar media with glucose.