Genetic characterization and evolutionary implications of a chromosomally encoded naphthalene-degradation upper...

Pseudomonas stutzeri strain AN10 is a naphthalene-degrading strain whose dissimilatory genes are chromosomally encoded. We sequenced a total of 11514bp including the entire naphthalene-degradation upper pathway (nah) of P. stutzeri AN10. Nine open reading frames, nahAaAbAcAdBFCED, encoding the enzymes for the degradation of naphthalene to salicylate, were identified. The nah genes of P. stutzeri AN10 have been compared with genes encoding isofunctional proteins from other Pseudomonas naphthalene-degradation upper pathways. The implications of the sequence homologies to the evolution of aromatic catabolic pathways are discussed. Our findings indicate that this entire catabolic module of P. stutzeri AN10 was recruited from other microorganisms and a short period of time has elapsed after its incorporation within the P. stutzeri AN10 genome. Comparisons also suggest the coexistence of two entire nah upper pathways in a host strain, and further recombination between them. These events could accelerate the evolution of modern catabolic pathways.