Molecular and biochemical characterization of the tetralin degradation pathway in Rhodococcus sp. strain TFB.

The tetralin biodegradation pathway in Rhodococcus sp. strain TFB, a Gram-positive bacterium resistant to genetic manipulation, was characterized using a proteomic approach. Relative protein expression in cell free extracts from tetralin- and glucose-grown cells was compared using the 2D-DIGE technique. Identification of proteins specifically expressed in tetralin-grown cells was used to characterize a complete set of genes involved in tetralin degradation by reverse genetics. We propose a tetralin degradation pathway analogous to that described for Sphingomonas macrogolitabida strain TFA. TFB thn genes are organized into three operons; two contain all of the structural genes and are transcribed in the same direction, while the third operon, thnST, is transcribed in the opposite direction and encodes a two-component regulatory system, whose transcription is higher in tetralin-grown cells. In addition to tetralin induction, TFB thn structural genes are subject to glucose repression. Primer extension assays and translational thnA1::gfp and thnS::gfp fusions were used to characterize putative promoter regions. A mutational analysis of the thnA1 promoter region allowed us to define nucleotides within the cis regulatory elements that are important for the control of thn gene expression.