Growth on dichlorobiphenyls with chlorine substitution on each ring by bacteria isolated from contaminated African soils

Abstract

Until recently, it was generally believed that the presence of more than one chlorine substituent prevented chlorinated biphenyls from serving as a sole source of carbon and energy for aerobic bacteria. In this study, we report the isolation of three aerobic strains, identified as Enterobacter sp. SA-2, Ralstonia sp. SA-4, and Pseudomonas sp. SA-6 from Nigerian polluted soils, that were able to grow on a wide range of dichlorobiphenyls (diCBs). In addition to growing on all monochlorobiphenyls (monoCBs), the strains were all able to utilize 2,2'-, 2,4'-, and 2,3-diCB as a sole source of carbon and energy. With the exception of strain SA-2, growth was also sustainable on 3,3'-, and 3,5-diCB. Washed benzoate-grown cells were typically able to degrade 68 to 100% of the diCB (100 ppm) within 188 h, concomitant with a cell number increase of up to three orders-of-magnitude and elimination of varying amounts of chloride. In many cases, stoichiometric production of a chlorobenzoate (CBA) as a product was observed. During growth on 2,2'-, and 2,4'-diCB, organisms exclusively attacked an o-chlorinated ring resulting in the production of 2-CBA and 4-CBA, respectively. A gradual decline in the concentration of the latter was observed, which suggested that the product was being degraded further. In the case of 2,3-diCB, the unsubstituted ring was preferentially metabolized. Initial diCB degradation rates were greatest for 2,4'-diCB (11.2 +/- 0.91 to 30.3 +/- 7.8 nmol/min per 10(9) cells) and lowest for 2,2'-diCB (0.37 +/- 0.12 to 2.7 +/- 1.2 nmol/min per 10(9) cells).

Pyrene-degradation potentials of Pseudomonas species isolated from polluted tropical soils

“…LP1 also performed better on chlorobenzoates tested than LP5 and LP6. One reason for this may be the fact that in the mechanic village where this organism was isolated, apart from oil products, other pollutants such as coils, capacitor, and transformer oil containing polychlorinated biphenyls (PCBs) abound and the selective pressure exerted by these pollutants led to acquisition of such special ability (Wackett and Hershberger 2001;Adebusoye et al 2007a).…”

Cometabolic degradation of polychlorinated biphenyls (PCBs) by axenic cultures of Ralstonia sp. strain SA-5 and Pseudomonas sp. strain SA-6 obtained from Nigerian contaminated soils

“…strain SA-5 and Pseudomonas sp. strain SA-6 to grow on broad and unusual spectrum of xenobiotic compounds including some congeners of diCBs, triCBs, di-and trichlorobenzenes as well as benzoate and naphthalene have been previously demonstrated (Adebusoye et al 2004(Adebusoye et al , 2007a. It was equally shown that growth of these strains were not sustainable on any tetraCBs tested.…”

“…The quantities of chloride released from this isomer into the culture media generally fell below 20% of the expected for total mineralization of the 3,4-dichlorophenyl ring. Our inability to achieve a mass balance between the substrate transformed and the 2,5-CBA and chloride recovered could in part be attributed to incomplete transformation of the PCB substrate to CBA (Furukawa et al 1979(Furukawa et al , 1983Yagi and Sudo 1980), or that the CBA formed was further metabolized to intermediate chlorinated products (Adebusoye et al 2007b). In the former, the results would suggest that at least some of the enzymes responsible for the various steps of the upper degradation pathway are far less tolerant of chlorines than the initial 2,3-dioxygenase.…”

“…Degradation experiments were conducted in chloride-free MS medium described previously (Adebusoye et al 2007b). Organisms were grown on MS medium supplemented with 2.5 mM benzoate at 25°C on an orbital shaker incubator (100 rpm; Labline Instruments Inc.).…”

“…Bacterial strains capable of growth on CBs and dichlorobiphenyls (diCBs) would be effective in degrading environmental mixtures of PCBs with the potential to offset the anticipated problems with the use of strain LB400 or H850. Interestingly, we have reported exceptional abilities of some bacterial strains obtained from tropical soils to grow with several congeners of CBs and diCBs (Adebusoye et al 2004(Adebusoye et al , 2007b as well as several congeners of chlorobenzenes and natural compounds (Adebusoye et al 2007a). In the current study, we report extensive degradation of Aroclor 1242 containing predominantly triCBs and tetrachlorobiphenyls (tetraCBs) by two of these bacterial strains namely, Ralstonia sp.…”