Isolation and characterization of microorganisms that degrade 4-chlorobiphenyl to 4-chlorobenzoic acid

Abstract

We designed a simple method that assesses the ability of aerobic microorganisms in soils to degrade 4-chlorobiphenyl (4-CB) to 4-chlorobenzoic acid. We screened bacteria in 46 soil samples collected from fields, paddy fields and gardens for strains that grew on biphenyl and degraded 4-CB. Sixty-five strains that utilized biphenyl were isolated from 21 (46%) of 46 soil samples, a high frequency. A simple screening method that used high-pressure liquid chromatography showed that 62 (95%) of the 65 strains that used biphenyl also degraded 4-CB. The results of metabolite analysis indicated that each isolate, without exception, produced 4-chlorobenzoic acid in a culture medium with a transitory yellow tinge. Metabolites of 4-CB were further investigated in an assay that used resting cells of Bacillus sp. strain TH 1171. The yellow metabolite was found to be 2-hydroxy-6-oxo-6-(4'-chlorophenyl) hexa-2,4-dienoic acid from the mass spectrum of its trimethylsilyl derivative. We examined the ability of the resting cells of strain TH 1171 incubated for 24h with a mixture of PCB congeners to degrade PCB by gas chromatography-mass spectrometry. Congeners 2-, 3-, and 4-chlorobiphenyl completely disappeared during incubation. 2,2'-, 2,3'-, and 2,4'-Dichlorobiphenyl and 2,4-, 2,5-, and 2,6-dichlorobiphenyl were transformed into mono- and dichlorobenzoic acids, respectively. The resulting degradation of 2,2'-, 2,3'-, and 2,4'-dichlorobiphenyl indicates that strain TH 1171 degrades chlorophenyl moieties of the PCB congeners. A possible biodegradation pathway of 4-CB via 2,3-dihydroxy-4'-chlorobiphenyl is proposed.