A fusion promoter created by a new insertion sequence, IS1490, activates transcription of 2,4,5-trichlorophenoxyacetic acid catabolic genes in Burkholderia cepacia AC1100

Abstract

Transposition and transcriptional activation by insertion sequences in Burkholderia cepacia AC1100 were investigated. Two closely related new elements, IS1413 and IS1490, were identified and characterized. These elements are not highly related to other insertion sequences identified in AC1100 or other B. cepacia isolates. Based on their structures and the sequences of the inverted terminal repeats and the putative transposase protein, the insertion elements (IS elements) are similar to IST2 of Thiobacillus ferrooxidans and several related elements. All the IS elements that have been identified in this strain are found in multiple copies (10 to 40), and they have high-level promoter activity capable of stimulating transcription from a distance up to 500 bp from a target gene. Strain AC1100 was originally isolated after prolonged selection for the ability to utilize the herbicide 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) as a sole carbon source. Three IS elements are located near the first gene of the 2,4,5-T catabolic pathway, tftA. IS1490 inserted 110 bp upstream of tftA and created a fusion promoter responsible for constitutive transcription of the gene. Our results confirm the hypothesis that IS elements play a central role in transcription of 2,4,5-T genes and likely have stimulated rapid evolution of the metabolic pathway.