Isolation and assessment of Pseudomonas aeruginosa and Bacillus cereus as PCB-degrading bacteria in environmental bioremediation

Classical methods of treatment of polychlorinated biphenyls (PCBs) in environmental matrices such as soil encapsulation, high-temperature heating, thermal desorption, and chemical decontamination, have been costly, and they leave behind problems of environmental footprints. They must therefore give way to bioremediation techniques which are less costly and result in ecofriendly products. The aim of the study was to assess the suitability of PCB degrading bacteria (using published data) from their environmental matrix for use in environmental bioremediation. Initial isolation of the bacteria was obtained by culturing ash samples taken from the combustion chamber of an MP400 Incinerator of infectious waste at Komfo Anokye Teaching hospital (KATH) in Kumasi, Ghana, and composite soil samples taken from a transformer-servicing site at an electricity substation in Sunyani, Ghana. Test for thermotolerance was carried out by the culturing of bacteria from the soil samples and exposing them to higher temperatures (55 degrees C and 65 degrees C) to assess their resilience in an incubator for 48 h. Growing cultures were sub-cultured, after which a cocktail of bacteria isolate characterization assays was carried out on the growing isolates. These included biochemical tests on the bacterial suspensions using the analytical profile index (API 20E) for examining Enterobacteriaceae and other non-fastidious bacteria. This was followed by MALDI-ToF-MS analyses of the bacterial strains to profile and image their proteins. A molecular step was needed which was the conventional polymerase chain reaction (PCR) method, using specific primer pairs, to amplify and accentuate sections of the bacterial DNA extracts. Results of the study showed a confirmed sample site in Ghana for harvesting bacteria capable of degrading polychlorinated biphenyls (PCBs). MALDI-ToF-MS analyses revealed the possible species as Pseudomonas aeruginosa and Bacillus cereus. The conventional PCR and gel electrophoresis steps confirmed the presence of bph genes encoding the 2,3-dioxygenase enzymes in bacteria with PCB-degrading ability as documented in published data. The serial dilution of the bacterial suspensions was modified from 10-7 to 10-5 which was enough for distinct colonies to be counted, and it was a novel contribution to environmental microbiology. The confirmation of Pseudomonas and Bacillus species isolated from a transformer oil-impacted soil in this study shows promise in growing these strains in various environmental media such as in a gaseous medium to mineralize gas -phase PCBs from combustion smoke or in bottom ash residues to degrade solidphase PCBs. It can also be applied in bioremediation of waste liquid systems containing PCBs.