J. Gen. Appl. Microbiol., 52, 125–130 (2006)

tants discharged from pulp and paper mills, tanneries, distilleries, dye and paint manufacturing and pharmaceuticals industry (Crosby, 1981). The major source of CPs is as by-products when chlorine is used for bleaching of pulp and for disinfections of drinking water. Therefore, large amounts of chlorinated aromatic compounds, including CPs, have been discharged into the environment (Steinle et al., 1998). Among chlorophenols, pentachlorophenol (PCP) is a wide spectrum biocide with applications in agriculture, industry and public health (Bevenue and Beckman, 1967). PCP a highly toxic pesticide has been widely used in disinfectants and preservatives (Rao, 1978). The U.S. Environmental Protection Agency regulates PCP as a priority pollutant and also considers 1.0 mg/L of PCP hazardous for land disposal (Freeman, 1989; Sittig, 1981). PCP is expected to be recalcitrant to aerobic biodegradation because it is highly chlorinated and, in general, aromatic compounds with higher amounts of chlorine are more resistant to biodegradation (Anandarajah et al., 2000). In addition, this compound is very harmful to microorganisms because it destroys membrane function due to its ability to uncouple oxidative phosphorylation (Copley, 2000; Ito and Ohnishi, 1982). In spite of these adverse properties, several microorganisms have been isolated from sites contaminated with PCP and their metabolite biodegradation pathways have been elucidated. In addition to this, different researchers have reported the PCP degrading microorganism (bacteria) from the natural environment. A number of microorganisms, Sphingomonas chlorophenolica formerly called Flavobacterium sp. (Chanama and Crawford, 1997), Mycobacterium chlorophenolicus, Mycobacterium fortuitum (Haggblom et al., 1988), Pseudomonas cepacia (Karns et al., 1983a, b), Pseudomonas sp. (Suzuki, 1977) and Rhodococcus sp. (Apajalahti and Salkinoje-Salonen, 1986), Corynebacterium sp. (Reiner et al., 1978), Arthrobacter sp. ATCC 33790 (Schenk et al., 1989) were found to metabolize PCP through chlorinated hydroquinone intermediates. There are still many unknown bacteria that have tremendous degradation capacity for PCP present in nature. Therefore, this study has emphasized the isoIsolation and characterization of two potential pentachlorophenol degrading aerobic bacteria from pulp paper effluent sludge