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

Abstract

Contaminated sites in Lagos, Nigeria were screened for the presence of chlorobiphenyl-degrading bacteria. The technique of continual enrichment on Askarel fluid yielded bacterial isolates able to utilize dichlorobiphenyls (diCBs) as growth substrates and six were selected for further studies. Phenotypic typing and 16S rDNA analysis classified these organisms as species of Enterobacter, Ralstonia and Pseudomonas. All the strains readily utilized a broad spectrum of xenobiotics as sole sources of carbon and energy. Growth was observed on all monochlorobiphenyls (CBs), 2,2'-, 2,3-, 2,4'-, 3,3'- and 3,5-diCB as well as di- and trichlorobenzenes Growth was also sustainable on Askarel electrical transformer fluid and Aroclor 1221. Time-course studies using 100 ppm of 2-, 3- or 4-CB resulted in rapid exponential increases in cell numbers and CB transformation to respective chlorobenzoates (CBAs) within 70 h. Significant amounts of chloride were recovered in culture media of cells incubated with 2-CB and 3-CB, suggesting susceptibilities of both 2- and 3-chlorophenyl rings to attack, while the 4-CB was stoichiometrically transformed to 4-CBA. Extensive degradation of most of the congeners in Aroclor 1221 was observed when isolates were cultivated with the mixture as a sole carbon source. Aroclor 1221 was depleted by a minimum of 51% and maximum of 71%. Substantial amounts of chloride eliminated from the mixture ranged between 15 and 43%. These results suggest that some contaminated soils in the tropics may contain exotic micro-organisms whose abilities and potentials are previously unknown. An understanding of these novel strains therefore, may help answer questions about the microbial degradation of polychlorinated biphenyls (PCBs) in natural systems and enhance the potential use of bioremediation as an effective tool for cleanup of PCB-contaminated soils.

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

“…However, like 3-CBA, the effect of this acid was more pronounced on the growth of strain SA-3. Additionally, both strains grew exponentially without lag phases in the presence of these acids similar to growth curves observed in their absence (Adebusoye et al 2007c). …”

“…During growth studies on CB congeners however, no apparent inhibition of growth or degradation by the build-up of CBA metabolites as dead-end products was observed (Adebusoye et al 2007c). The concentration of CBA possibly liberated to the medium by the partial degradation of the congeners is negligible in comparison with the combined CBA concentration added.…”

“…SA-6 capable of utilizing all monochlorobiphenyls (CBs) and some dichlorobiphenyls were isolated from transformer-fluid contaminated soils in Lagos, Nigeria after several months of enrichment cultivation on Askarel fluid and Aroclor 1221 as the sole carbon source. Identification of these strains was based on the sequencing of the full-length 16S rRNA genes coupled with phenotypic characterization using API 20 E system (bioMerieux Vitek, Inc. Hazelwood, MO) as previously described (Adebusoye et al 2007c). The 16S rRNA gene sequences have since been deposited in the GenBank database under the accession numbers DQ854840, DQ854842, DQ854843, DQ854845, and DQ854841 respectively for strains SA-1, SA-2, SA-3, SA-5, and SA-6.…”

Enrichment and Identification of Askarel oil (PCB blend) degrading bacteria enriched from landfill sites in Edo State, Nigeria

“…(Furukawa et al, 1979;Bopp 1986;Bedard et al, 1987, Kim and Picardal 2000and Adebusoye et al, 2008. However these notable achievements, in most developing countries such as Nigeria most PCB items and PCB waste oils are discharged into the environment without proper monitoring and determination of the fate of such compounds (Adebusoye et al, 2008). Furthermore from research studies, the isolation and studies on degradation of PCB item and its derivatives (transformer oil) in Nigeria is still at its infancy.…”

Decrease of the level of extractable polychlorinated biphenyls in soil microcosms: Influence of granular activated carbon and inoculation by natural microbial consortia

“…This family of 209 molecules, consisting of a biphenyl core with one to nine chlorine atoms, was used in numerous applications such as insulation, lubrication, pesticide extension, adhesion, heat transfer, sealing, painting, and carbonless copy paper during the 20th century. Although its applications were severely regulated, contaminated soils are still found near old transformers and industrial sites (Adebusoye et al, 2008;Vasilyeva et al, 2010) and PCBs represent an ubiquitous source of pollution.…”