Once widely used, polychlorinated biphenyls, or PCBs, are now classified as a highly toxic priority pollutant. PCB contamination is prevalent in former industrial areas, and affects surrounding land and water environments. The toxic threat of PCBs entering the human food supply emphasizes the importance of effective removal. Microbes acting as PCB degraders are isolated from soil and sewage treatment plants in a process known as bioremediation.
PCB Degraders
Scientists have already identified microbes that degrade lesser toxic PCBs. Research into isolating strains with greater degrading ability is ongoing, the majority of which focuses on aerobic bacteria isolated from soil. Various species of fungi are also known for degrading priority pollutants, including complex, insoluble organic compounds that may remain unaffected by bacteria.
PCB Degradation
PCB degradation involves the introduction of hydroxyl groups into a PCB molecule via dioxygenase enzyme action. The adherence to lipid molecules is sequentially lowered, causing oxidation and aromatic ring cleavage. As these are considered the rate-limiting steps of the process, the susceptibility of PCBs to degradation is likely to increase.
Biphenyls
Biphenyl is a potential carbon source for bacteria, and may also induce degradation pathways. Based on this, potential PCB degraders are isolated by culturing bacterial strains in media containing biphenyl. An acetonic spray is then used to identify biphenyl degradation, by measuring the yellow compound 2-hydroxy-6-oxo-6-phenyl-hexa-2, 4-dienoic acid, produced as a metabolite.
Ligninolytic Enzymes
Several fungi species contain ligninolytic enzymes, capable of degrading lignin. Measurement of enzyme activity is applied when isolating fungi. Fungi grown in media containing PCB, glucose, and other minerals undergo agar dilution in the presence of Poly R478 dye. Scientists believe decomposition of this dye by ligninolytic enzymes to be directly proportional to that of PCBs, which makes this process a useful indication of fungi degradation potential.
