Degradation of anaerobic reductive dechlorination products of Aroclor 1242 by four aerobic bacteria

We studied the aerobic degradation of eight PCB congeners which comprise from 70 to 85% of the anaerobic dechlorination products from Aroclor 1242, including 2-, 4-, 2,4-, 2,6-, 2,2'-, 2,4'-, 2,2',4-, and 2,4,4'-chlorobiphenyl (CB), and the biodegradation of their mixtures designed to simulate anaerobic dechlorination profiles M and C. Strains Comamonas testosteroni VP44 and Rhodococcus erythreus NY05 preferentially oxidized a para-substituted ring, while Rhodococcus sp. RHA1, similar to well known strain Burkholderia sp. LB400, preferably attacked an ortho-chlorinated ring. Strains with ortho-directed attack extensively degraded 2,4'- and 2,4,4'-CB into 4-chlorobenzoate, while bacteria with para-directed attack transformed these congeners mostly into potentially problematic meta-cleavage products. The strains that preferentially oxidized an ortho-substituted ring readily degraded seven of the eight congeners supplied individually; only 2,6-CB was poorly degraded. Degradation of 2,2'- and 2,4,4'-CB was reduced when present in mixtures M and C. Higher efficiencies of degradation of the individual congeners and defined PCB mixtures M and C and greater production of chlorobenzoates were observed with bacteria that preferentially attack an ortho-substituted ring. PCB congeners 2,4'-, 2,2',4-, and 2,4,4'-CB can be used to easily identify bacteria with ortho-directed attack which are advantageous for use in the aerobic stage of the two-phase (anaerobic/aerobic) PCB bioremediation scheme.