Styrene lower catabolic pathway in Pseudomonas fluorescens ST: identification and characterization of genes for phenylacetic acid degradation

Pseudomonas fluorescens ST is a styrene degrading microorganism that, by the sequential oxidation of the vinyl side chain, converts styrene to phenylacetic acid. The cluster of styrene upper pathway catabolic genes (sty genes) has been previously localized on a chromosomal region. This report describes the isolation, sequencing and analysis of a new chromosomal fragment deriving from the ST strain genomic bank that contains the styrene lower degradative pathway genes (paa genes), involved in the metabolism of phenylacetic acid. Analysis of the paa gene cluster led to the description of 14 putative genes: a gene encoding a phenylacetyl-CoA ligase (paaF), the enzyme required for the activation of phenylacetic acid; five ORFs encoding the subunits of a ring hydroxylation multienzymatic system (paaGHIJK); the gene paaW encoding a membrane protein of unknown function; five genes for a β-oxidation-like system (paaABCDE), involved in the steps following the aromatic ring cleavage; a gene encoding a putative permease (paaL) and a gene (paaN) probably involved in the aromatic ring cleavage. The function of some of the isolated genes has been proved by means of biotransformation experiments.