Preliminary characterization of four 2-chlorobenzoate-degrading anaerobic bacterial consortia

Dechlorination was the initial step of 2CB biodegradation in four 2-chlorob enzoate-degrading methanogenic consortia. Selected characteristics of ortho reductive dehalogenation were examined in consortia developed from the hig hest actively dechlorinating dilutions of the original 2CB consortia, desig nated consortia M34(-9), P20(-9), P21(-9) and M50(-7). In addition to 2-chl orobenzote, all four dilution consortia dehalogenated 4 of 32 additional ha logenated aromatic substrates tested, including 2-bromobenzoate; 2,6-dichlo robenzoate; 2,4-dichlorobenzoate; and 2-chloro-5-hydroxybenzoate. Dehalogen ation occurred exclusively at the ortho position. Both ortho chlorines were removed from 2,6-dichlorobenzoate. Benzoate was detected from 2-bromobenzo ate and 2,6-dichlorobenzoate. 4-Chlorobenzoate and 3-hydroxybenzoate were f ormed from 2,4-dichlorobenzoate and 2-chloro-5-hydroxybenzoate, respectivel y. Only benzoate was further degraded. Slightly altering the structure of t he parent "benzoate molecule'' resulted in observing reductive biotransform ations other than dehalogenation. 2-Chlorobenzaldehyde was reduced to 2-chl orobenzyl alcohol by all four consortia. 2-chloroanisole was O-demethoxylat ed by three of the four consortia forming 2-chlorophenol. GC-MS analysis in dicated reduction of the double bond in the propenoic side chain of 2-chlor ocinnamate forming 2-chlorohydrocinnamate. None of the reduction products w as dechlorinated. The following were not dehalogenated: 3- and 4-bromobenzo ate; 3- and 4-chlorobenzoate; 2-, 3-, and 4-fluorobenzoate; 2-, 3-, and 4-i odobenzoate; 2-, 3-, and 4-chlorophenol; 2-chloroaniline; 2-chloro-5-methyl benzoate; 2,3-dichlorobenzoate; 2,5-dichlorobenzoate; 2,4,5-trichlorophenox yacetic acid; and 2,4-dichlorophenoxyacetic acid. Consortia M34(-9), P20(-9 ), P21(-9), and M50(-7) dechlorinated 2-chlorobenzoate at less than or equa l to 4 mm. Dechlorination rates were highest for consortia P20-9 followed b y those of M50(-7) with rates declining above 2 and 3mm 2CB, respectively. The major physiological types of microorganisms in consortia M34(-9), P20(- 9), P21(-9), and M50(-7) were sulfate-reducing and hydrogen-utilizing anaer obes.