Biodegradation of chlorophenols by pure and mixed cultures of isolated microorganisms

Abstract

Three strains to degrade chlorophenols were isolated through a selective enrichment procedure with 2,4,6-trichlorophenol (TCP) and 4-chlorophenol (4-CP). On the basis of their morphological and phenotypic characteristics, TCP degrading strain was identified as Pseudomonas solanacearum TCP114, and two 4-CP degrading strains were done as Pseudomonas testosteroni CPW301 and Arthrobacter ureafaciens CPR706, respectively. A 4-CP degrading bacterium, Pseudomonas testosteroni CPW301, dechlorinated and degraded 4-CP via a meta-cleavage pathway. CPW301 could also utilize phenol as a carbon and energy source without the accumulation of any metabolites. Resting cell experiments and enzyme assays of the cell extract indicated that both 4-CP and phenol were degraded via the same meta-cleavage pathway. When phenol was added as a secondary substrate, CPW301 could degrade 4-CP and phenol simultaneously. The addition of phenol enhanced the 4-CP degradation rate greatly because of the increased cell mass and 4-CP degradation activity. Another 4-CP degrading strain, Arthrobacter ureafaciens CPR706, produced hydroquinone as transient intermediate of 4-CP degradation. This result indicated that the chloro-substituent of 4-CP was eliminated to form hydroquinone, which was demonstrated to be oxidized by enzyme extracts from 4-CP grown cells. CPR706 exhibited much higher tolerance for 4-CP than CPW301, as indicated by the maximum degradable concentration (1.6 mM for CPR706 and 0.8 mM for CPW301). The average 4-CP degradation rate by CPR706 was 13 fold higher than that by CPW301 due to the better specific degradation rate and cell yield of CPR706 (0.32 g cell/g 4-CP) than those of CPW 301. CPR706 was demonstrated to degrade other para-substituted phenols through hydroquinone. The degradability of one component by a pure culture was strongly affected by the presence of other compounds in the medium. For example, when all three components (TCP, 4-CP, and phenol) were present in the me...