Expression of Salmonella typhimurium genes required for invasion is regulated by changes in DNA supercoiling

Abstract

The ability to enter intestinal epithelial cells is an essential virulence factor of salmonellae. We have previously cloned a group of genes (invA, B, C, and D) that allow S. typhimurium to penetrate tissue culture cells (J. E. Galan and R. Curtiss III, Proc. Natl. Acad. Sci. USA 86:6383-6387, 1989). Transcriptional and translational cat and phoA fusions to invA (the proximal gene in the invABC operon) were constructed, and their expression was studied by measuring the levels of alkaline phosphatase or chloramphenicol acetyltransferase activity in mutants grown under different conditions. It was found that when strains containing the fusions were grown on media with high osmolarity, a condition known to increase DNA superhelicity, the level of invA transcription was approximately eightfold higher than that in strains grown on media with low osmolarity. The osmoinducibiity of invA was independent of ompR, which controls the osmoinducibility of other genes. Strains grown in high-osmolarity media in the presence of subinhibitory concentrations of gyrase inhibitors (novobiocin or coumermycin Al), which reduce the level of DNA supercoiling, showed reduced expression of invA. Nevertheless, invA was poorly expressed in topA mutants of S. typhimurium, which have increased DNA superhelicity. In all cases, the differential expression of the invasion genes was correlated with the ability of S. typhimurium to penetrate tissue culture cells. These results taken together indicate that expression of S. typhimurium invasion genes is affected by changes in DNA supercoiling and suggest that this may represent a way in which this organism regulates the expression of these genes.

Comparison of type III secretion system virulence among fluoroquinolone-susceptible and -resistant clinical isolates of Pseudomonas aeruginosa

“…Concomitantly, development of mutations conferring resistance to fluoroquinolones as a result of heavy exposure may have occurred, either in parallel or following an assortive recombination of chromosomal regions encoding resistance and virulence genes [34]. Alternatively, Preisler et al [35] have reported that the gyrA mutations that confer fluoroquinolone resistance also affect supercoiling of DNA, which has been shown to affect virulence gene expression [36][37][38]. Other studies have revealed that inhibition of DNA gyrase with antibiotics (i.e., novobiocin) specifically affects transcription of type III virulence genes [36][37][38][39].…”

“…Alternatively, Preisler et al [35] have reported that the gyrA mutations that confer fluoroquinolone resistance also affect supercoiling of DNA, which has been shown to affect virulence gene expression [36][37][38]. Other studies have revealed that inhibition of DNA gyrase with antibiotics (i.e., novobiocin) specifically affects transcription of type III virulence genes [36][37][38][39]. Thus, the potential for fluoroquinolone resistance to affect TTSS gene expression as a result of changes in DNA supercoiling has already been demonstrated in other bacterial species [36,37].…”

Oral delivery of DNA vaccines using attenuated Salmonella typhimurium as carrier

“…The transmigration of M cells by Salmonella is an active process which requires the induction of genes encoded by so-called pathogenicity islands. Such genes are strongly induced when Salmonella are grown under anaerobic conditions and high salt [15,16]. To take this into consideration, cultures were always grown without aeration.…”

Aptameric enzyme subunit for homogeneous DNA sensing

“…We designed a thrombin-inhibiting aptamer, to which we attached 36-, 27-or 18-mer complementary sequences of target DNAs at its 5 0 or 3 0 end. We used three different DNA sequences as the target DNAs: a part of the Salmonella invA gene (nucleotide positions 426 to 452) was used for the AES invA series (Galan et al 1990), a part of the SARS coronavirus genomic antisense sequence (genome location 15348 to 15383) (Rota et al 2003;Marra et al 2003) for the AES SARS 1 series and a part of the SARS coronavirus genomic sequence (genome location 15561 to 15596) for the AES SARS 2 series. The 36-, 27-and 18-mer DNA sequences were used as the target DNAs, and these complementary strands were added to the thrombin-inhibiting aptamer at its 5 0 or 3 0 end.…”