NTN GENES DETERMINING THE EARLY STEPS IN THE DIVERGENT CATABOLISM OF 4-NITROTOLUENE AND TOLUENE IN PSEUDOMONAS SP - STRAIN TW3

Pseudomonas sp. strain TW3 is able to oxidatively metabolize 4-nitroto luene and toluene via a route analogous to the upper pathway of the TO L plasmids. We report the sequence and organization of five genes, ntn WCMAB, which are very similar to and in the same order as the xyl ope ron of TOL plasmid pWW0 and present evidence that they encode enzymes which are expressed during growth on both 4-nitrotoluene and toluene a nd are responsible for their oxidation to 4-nitrobenzoate and benzoate , respectively. These genes encode an alcohol dehydrogenase homolog (n tnW), an NAD(+)-linked benzaldehyde dehydrogenase (ntnC), a two-gene t oluene monooxygenase (ntnMA), and part of a benzyl alcohol dehydrogena se (ntnB), which have 84 to 99% identity at the nucleotide and amino acid levels with the corresponding xylWCMAB genes. The xylB homolog on the TW3 genome (ntnB) appears to be a pseudogene and is interrupted by a piece of DNA which destroys its functional open reading frame, im plicating an additional and as-yet-unidentified benzyl alcohol dehydro genase gene in this pathway. This conforms with the observation that t he benzyl alcohol dehydrogenase expressed during growth on 4-nitrotolu ene and toluene differs significantly from the XylB protein, requiring assay via dye-linked electron transfer rather than through a nicotina mide cofactor. The further catabolism of 4-nitrobenzoate and benzoate diverges in that the former enters the hydroxylaminobenzoate pathway a s previously reported, while the latter is further metabolized via the beta-ketoadipate pathway.