Biphenyl is an aromatic hydrocarbon with some toxicity. A number of bacteria are able to initiate the degradation of the compound by adding molecular oxygen to the ring. Pseudomonia sp. strain LB 400 is particularly noteworthy. It encodes four enzymes and catabolizes biphenyl to benzoate and 2-hydroxypenta-2,4-dienoate through four steps, often called the biphenyl upper pathway. Interestingly, after growth with biphenyl, many bacteria can oxidize polychlorinated biphenyls (PCBs), a group of man-made compounds composed of biphenyl molecules containing from 1 to 10 chlorines, and persistent and toxic in biophere. It has been shown that PCBs follow the same catabolic pathway as biphenyl and use the same enzymes. Biphenyl dioxygenase plays a critical role in PCB degradation by catalyzing the first step. Its activity varies depending on the number of chlorines and their positions on the aromatic ring. The EAWAG-BBD also contains the biodegradation pathway for one model PCB, 4-chlorobiphenyl. This pathway is a description of the upper pathway for metabolism of biphenyl as encoded by the bph locus of Pseudomonas sp. strain LB400 as described by [http://www.ncbi.nlm.nih.gov/pubmed/95344182|Seeger, et al. (1995)].