Bacterial Degradation and Bioremediation of Chlorinated Herbicides and Biphenyls

Chlorinated herbicides (e.g. s-triazines) and polychlorobiphenyls (PCBs) are persistent organic pollutants (POPs) that are widely distributed in the environment. s-Triazine herbicides are used in agriculture and forestry in diverse regions of the world. PCBs were produced worldwide for industrial applications, and an important amount of these compounds have been released into the environment. PCBs and s-triazines are toxic compounds that could act as endocrine disrupters and cause cancer. Therefore, environmental pollution with s-triazines and PCBs is of increasing concern. Bioremediation is an attractive technology for the decontamination of polluted sites. Microorganisms play a main role in the removal of POPs from the environment. Diverse bacteria able to degrade s-triazines and PCBs have been characterized. Bacterial degradation of s-triazine herbicides involves hydrolytic reactions catalyzed by amidohydrolases encoded by the atz genes. Anaerobic and aerobic bacteria are capable of biotransforming PCBs. Higher chlorinated PCBs are subjected to reductive dehalogenation by anaerobic microorganisms. Lower chlorinated biphenyls are oxidized by aerobic bacteria. Genome analyses of PCB-degrading bacteria have increased the knowledge of their metabolic capabilities and their adaptation to stressful conditions. For the removal of s-triazines and PCBs from the environment, efficient bioremediation processes have to be established. In this report, bacterial degradation of s-triazines and PCBs is described and novel strategies to improve bioremediation of these POPs are discussed.