Evolutionary relationship of biphenyl-catabolic genes in soil bacteria

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Biphenyl(BP) utilizing bacteria are widely distributed in the environment. Thirty two different BP-strains isolated far clasified into four groups according to the homologies of BP-catabolic bph genes and immunological properties of BP-ring-cleavage dioxygenases. The bph operon of Pseudomonas pseudoalcaligenes KF707 is organized as bphA1A2A3A4BCXD.Biphenyl dioxygenase is a multi-component enzyme which composed of large subunit(encoded by bphA1) and small subunit(encoded by bphA2)of terminal deioxygenase, ferredoxin(encoded by bphA3)and ferredoxin reductase(encoded by bphA4). bphB encodes BP-dihydrodiol dehydrogenase, bphC encodes BP-ring meta-cleavage dioxygenase, and bphD encodes hydrolase. The bph operon is very similar to toluene catabolic tod operon of Pseudomonas putida F1 in the gene organization and nucleotide sequences. The gene components responsible for substrate specificity between the bph and tod operons were investigated. The large and small subunits of the terminal dioxygease and the ring meta-cleavage compound hydrolase were critical for their discrete metabolic specificities. From the results obtained in this study it can be postulated that BP-utilizing bacteria, along with other aromatics utilizing bacteira, might be involved in the final degradation of plant lignin.