Bacterial PCB biodegradation

Abstract

The environment has become polluted with a variety of xenobiotics, including PCBs, as a result of the industrial development of useful halogenated compounds. While the PCBs may not exhibit the acute toxicity originally ascribed to them, they and their attendant byproducts remain as significant factors for adverse effects in the ecological food-chain. The use of microorganisms for bioremediation of PCBs is reviewed. This paper further details three new isolates obtained by conventional enrichment technics which show significant degradation capabilities for Aroclor 1242. These were identified by morphology, staining, and fatty acid analysis as Comamonas testosteroni, Rhodococcus rhodochrous, and a strain of Pseudomonas putida. These isolates demonstrated somewhat selective degradations of the congeners within Aroclor 1242; comprising total losses of 13.8, 19.1, and 24.6%, respectively. Each organism can attack dichloro-through tetrachlorobiphenyls. Analysis of chromatographic patterns from anaerobically digested Aroclor 1242 samples treated by these bacteria demonstrated decreases in di- through penta-substituted biphenyls. Each of these isolates, with discrete specificities, showed preferences for ‘open’ 2,3-sites, indicative of the action of 2,3-dioxygenase enzymes. The identification of many intermediates in the foregoing transformations was established by GC-MS analyses. Several variations in metabolic pathways, centering on the meta cleavage product 2-hydroxy-6-oxo-6-phenylhexa-2,4-dienoic acid (HOPDA) were suggested from these data. It is concluded that the described strains may be of future bioremediation use in processes which have an initial anaerobic dechlorination stage.