Dehalogenase genes of Pseudomonas putida PP3 on chromosomally located transposable elements

Pseudomonas putida PP3 utilizes halogenated alkanoic acids (HAA) such as 2,2-DCPA as its sole carbon and energy sources. Spontaneous HHA- mutants, isolated by selection for resistance to the toxic analogs monochloroacetic acid and dichloroacetic acid, arose at frequencies several orders of magnitude higher than expected for spontaneous mutations. Analysis of the five classes of mutants isolated suggested that the dehalogenase and HAA permease genes were on chromosomally located transposable elements and that the spontaneous mutations involved excision of these elements. This suggestion was confirmed by the observation that one of the elements can transpose to a target DNA molecule. The frequency of the excision event was strongly influenced by environmental conditions. Possible relationships between expression of cryptic genes and their location on transposable elements are discussed.