Genetic characterization and evolutionary implications of a chromosomally encoded naphthalene-degradation upper pathway from Pseudomonas stutzeri AN10

Pseudomonas stutzeri strain AN10 is a naphthalene-degrading strain whose di ssimilatory genes are chromosomally encoded. We sequenced a total of 11514 bp including the entire naphthalene-degradation upper pathway (nah) of P. s tutzeri AN10. Nine open reading frames, nahAaAbAcAdBFCED, encoding the enzy mes for the degradation of naphthalene to salicylate, were identified. The nah genes of P. stutzeri AN10 have been compared with genes encoding isofun ctional proteins from other Pseudomonas naphthalene-degradation upper pathw ays. The implications of the sequence homologies to the evolution of aromat ic catabolic pathways are discussed. Our findings indicate that this entire catabolic module of P, stutzeri AN10 was recruited from other microorganis ms and a short period of time has elapsed after its incorporation within th e P. stutzeri AN10 genome. Comparisons also suggest the coexistence of two entire nah upper pathways in a host strain, and further recombination betwe en them. These events could accelerate the evolution of modern catabolic pa thways. (C) 1999 Elsevier Science B.V. All rights reserved.