Transposition of Pseudomonas toluene-degrading genes and expression in Escherichia coli

Abstract

PLASMIDS contribute to the metabolic versatility of soil pseudomonads by specifying enzymes responsible for the oxidation of unusual organic substrates^1,2. TOL plasmids determine an inducible sequence of enzymes that oxidise toluene, m-xylene, and p-xylene via alcohol and aldehyde intermediates to benzoate, m-toluate, and p-toluate, respectively, which are further metabolised by ring fission via the meta (or α-ketoacid) pathway—the enzymes of which also plasmid determined^3–5. TOL plasmids found in soil Pseudomonas strains⁶ are notably heterogeneous in molecular properties⁷. Analogous observations on the heterogeneity of plasmids carrying the genes for TEM-type β-lactamase⁸ led to the demonstration that this gene was promiscuously transposable between plasmids of Gram-negative bacteria⁹. We have found that tol genes can be transposed to other plasmids, including the broad host range plasmid RP4. Such a derivative, RP4-tol, allows the expression of a specialised Pseudomonas pathway to be studied in Escherichia coli. In this foreign host tol gene function can be detected but at a much lower level than in Pseudomonas.