Nucleotide sequence and functional analysis of the genes encoding 2,4,5-trichlorophenoxyacetic acid oxygenase in Pseudomonas cepacia AC1100

Abstract

Pseudomonas cepacia AC1100 is able to use the chlorinated aromatic compound 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) as the sole source of carbon and energy. One of the early steps in this pathway is the conversion of 2,4,5-T to 2,4,5-trichlorophenol (2,4,5-TCP). 2,4,5-TCP accumulates in the culture medium when AC1100 is grown in the presence of 2,4,5-T. A DNA region from the AC1100 genome has been subcloned as a 2.7-kb SstI-XbaI DNA fragment, which on transfer to Pseudomonas aeruginosa PAO1 allows the conversion of 2,4,5-T to 2,4,5-TCP. We have determined the directions of transcription of these genes as well as the complete nucleotide sequences of the genes and the number and sizes of the polypeptides synthesized by pulse-labeling experiments. This 2.7-kb DNA fragment encodes two polypeptides with calculated molecular masses of 51 and 18 kDa. Proteins of similar sizes were seen in the T7 pulse-labeling experiment in Escherichia coli. We have designated the genes for these proteins tftA1 (which encodes the 51-kDa protein) and tftA2 (which encodes the 18-kDa protein). TftA1 and TftA2 have strong amino acid sequence homology to BenA and BenB from the benzoate 1,2-dioxygenase system of Acinetobacter calcoaceticus, as well as to XylX and XylY from the toluate 1,2-dioxygenase system of Pseudomonas putida. The Pseudomonas aeruginosa PAO1 strain containing the 2.7-kb SstI-XbaI fragment was able to convert not only 2,4,5-T to 2,4,5-TCP but also 2,4-dichlorophenoxyacetic acid to 2,4-dichlorophenol and phenoxyacetate to phenol.