Microbial Growth on Dichlorobiphenyls Chlorinated on Both Rings as a Sole Carbon and Energy Source

Abstract

We have isolated bacterial strains capable of aerobic growth on ortho-substituted dichlorobiphenyls as sole carbon and energy sources. During growth on 2,2-dichlorobiphenyl and 2,4-dichlorobiphenyl strain SK-4 produced stoichiometric amounts of 2-chlorobenzoate and 4-chlorobenzoate, respectively. Chlorobenzoates were not produced when strain SK-3 was grown on 2,4-dichlorobiphenyl.Although bioremediation is an effective cleanup strategy for many contaminants, efforts to engineer bioremediation systems for polychlorinated biphenyl (PCB)-contaminated soils or sludges have been largely ineffective. One of the more promising PCB bioremediation strategies is sequential anaerobicaerobic treatment (1). Under anoxic conditions, highly chlorinated congeners can often be reductively dechlorinated (8,25), resulting in congeners that can potentially be degraded by aerobic bacteria. The lightly chlorinated congeners (one to five chlorines) remaining after reductive dechlorination can be either utilized as an aerobic growth substrate (12, 16) or cometabolically degraded in the presence of biphenyl (9,14).With few exceptions (5, 10), anaerobic PCB dechlorination rarely occurs at the ortho positions and generally results in accumulation of ortho-or ortho-and para-substituted congeners (19,21,27,28). Interestingly, ortho substitution of a PCB also greatly reduces aerobic biodegradability (4, 13). As reported by Furukawa (11), PCB isomers with two ortho chlorines, such as 2,2Ј-dichlorobiphenyl (2,2Ј-CB) or 2,6-CB, are rarely susceptible to aerobic cometabolic degradation. As a consequence, limited aerobic degradation of ortho-substituted congeners is a weak link in the development of effective anaerobic-aerobic PCB bioremediation strategies. Possible accumulation of ortho-substituted congeners such as 2,2Ј-CB may also have ecological and human health implications (7,22).Although numerous reports have shown that monochlorobiphenyls can serve as growth substrates (2,3,6,17,18,23), reports of unambiguous growth by natural isolates on CBs has been demonstrated only for Burkholderia sp. strain LB400 (20). To the best of our knowledge, growth on a di-ortho-substituted CB has not been demonstrated. Here we report the isolation and characterization of unique bacteria capable of using as growth substrates ortho-substituted CB congeners with chlorine substituents on both rings, including an isolate able to utilize 2,2Ј-CB.The CB-degrading bacteria were isolated from PCB-contaminated, tertiary lagoon sludge as previously described (16). One isolate (SK-3) was selected based on its ability to grow on both 4-chlorobiphenyl and 4-chlorobenzoic acid (4-CBA) (16). Another isolate (SK-4) was ultimately enriched and selected based on an ability to grow on 2,2Ј-CB.Cell growth and biotransformation of CBs were studied in Balch tubes sealed with Teflon-coated stoppers as reported previously (16). Experiments were done in a mineral salts medium (16) which was amended with 5 or 10 l of a solution of a single PCB congener dissolved in heptamethylnonane (...

Characterization of multiple novel aerobic polychlorinated biphenyl (PCB)-utilizing bacterial strains indigenous to contaminated tropical African soils

“…LB400, have been reported to possess an exceptional ability to degrade even a larger range of congeners including penta-and hexachlorobiphenyl co-metabolically (Bopp 1986;Bedard et al 1987a, b;Commandeur et al 1996;Potrawfke et al 1998). These other micro-organisms, however, have not been shown to utilize the range of xenobiotics reported for SA-2 (or any of the SA strains) in this investigation for growth as sole carbon sources (McCullar et al 1994;Kim and Picardal 2001;Rodrigues et al 2006).…”

Influence of chlorobenzoic acids on the growth and degradation potentials of PCB-degrading microorganisms

“…The process of PCBs bioremediation is still inefficient and not well established in spite of the existing body of knowledge on microbial biodegradation of these xenobiotics. Most PCB degraders are only able to biotransform these compounds to CBAs as dead-end products (Kobayashi et al 1996;Kim and Picardal 2001;Rodrigues et al 2006;Adebusoye et al 2007b, c). The biodegradation performance of the scavenging organism could be affected by the toxicity of the metabolites (Stratford et al 1996;Vrana et al 1996; Table 1 Growth of Ralstonia Values are means ± standard deviations for three replicate samples Fig.…”

Cometabolic degradation of mono-chloro benzoic acids by Rhodococcus sp. R04 grown on organic carbon sources

“…Chlorobenzoic acids (CBAs) generally are transformed slowly by aerobic PCB-degrading bacteria, degradation of which appeared to be the rate limiting step in the overall PCB-degradation process (Adriaens and Focht 1991a), although there was reports that bacteria in principal are able to use chloroaromatics as growth substrates with total elimination of chloride (Kim and Picardal 2001). Due to their toxicity, bacterial growth on halogenated aromatics as sole energy and carbon source is often suboptimal, showing long acclimation lag and slow growth rates.…”