Evidence for novel mechanisms of polychlorinated biphenyl metabolism in Alcaligenes eutrophus H850

Abstract

Previous studies indicated that Alcaligenes eutrophus H850 attacks a different spectrum of polychlorinated biphenyl (PCB) congeners than do most PCB-degrading bacteria and that novel mechanisms of PCB degradation might be involved. To delineate this, we have investigated the differences in congener selectivity and metabolite production between H850 and Corynebacterium sp. strain MB1, an organism that apparently degrades PCBs via a 2,3-dioxygenase. H850 exhibited a superior ability to degrade congeners via attack on 2-, 2,4-, 2,5-, or 2,4,5-chlorophenyl rings in PCBs but an inferior ability to degrade congeners via attack on a 4-chlorophenyl ring. Reactivity preferences were also reflected in the products formed from unsymmetrical PCBs; thus MB1 attacked the 2,3-chlorophenyl ring of 2,3,2',5'-tetrachlorobiphenyl to yield 2,5dichlorobenzoic acid, while H850 attacked the 2,5-chlorophenyl ring to yield 2,3-dichlorobenzoic acid and a novel metabolite, 2',3'-dichloroacetophenone. Furthermore, H850 oxidized 2,4,5,2',4',5'-hexachlorobiphenyl, a congener with no adjacent unsubstituted carbons, to 2',4',5'-trichloroacetophenone. The atypical congener selectivity pattern and novel metabolites produced suggest that A. eutrophus H850 may degrade certain PCB congeners by a new route beginning with attack by some enzyme other than the usual 2,3-dioxygenase.

Degradation of Aroclor 1221 in soil by a hybrid pseudomonad

“…Complete mineralization of PCBs cannot be achieved solely by anaerobic or aerobic natural microbial populations. Under aerobic conditions, degradation of chlorinated congeners stops at different stages so that chlorophenylcatechols, 215 meta-cleavage products, chloroacetophenones and chlorobenzoates accumulate as dead-end metabolites [4][5][6][7][8][9][10][11][12]. In contrast, anaerobic microbial treatment of PCB contaminated material leads to orthoand para-substituted less chlorinated congeners [13-17] which will not be degraded further.…”

Effects of 2,2′,5,5′-tetrachlorobiphenyl and biphenyl on cell membranes of Ralstonia eutropha H850

“…eutropha (formerly Alcaligenes eutrophus) H850 was obtained from the U.S. Department of Agriculture (USDA). The growth medium and conditions were as described by Bedard et al [15]. For membrane polarization and fatty acid analysis, cultures were grown to mid-exponential phase at 30³C in the same medium containing 0.1% (w/v) of either biphenyl or fructose as the sole carbon source.…”

Ecological fate, effects and prospects for the elimination of environmental polychlorinated biphenyls (PCBs)

“…Ortho cleavage of the 2,3 diol has been proposed as another alternative pathway for chlorobiphenyl dissimilation [94]. Products (primarily acetophenones) from this type of cleavage have been reported from PCB mixtures [81, 95], from 2-chlorobiphenyl [79] and from 4-chlorobiphenyl [96,97].…”