| Mycoplasma genitalium is the smallest self-replicating bacterium and the causative agent of a spectrum of urogenital diseases. Similar to other mycoplasmas, transcriptional regulation remains poorly understood in M. genitalium because of the lack of many regulatory genes due to a streamlined genome (0.58 Mb). Although M. genitalium has been shown to selectively induce the expression of heat shock genes though conserved mechanism, it remains unknown whether and how M. genitalium can regulate transcription of genes in response to other environmental signals likely to be encountered in vivo.;This project was to characterize the transcriptional changes of M. genitalium in response to osmolarity changes, an environmental condition M. genitalium encounters in human urethral tract as a urogenital pathogen, and investigate the mechanism involved in transcriptional regulation. First, using an oligonucleotide-based whole genome microarray, a set of genes was identified differentially expressed (39 upregulated and 72 downregulated) upon treating M. genitalium with 0.3 M sodium chloride (NaCl) for 1 h. Second, the mechanism underlying the upregulation of MG_149, a lipoprotein-encoding gene, was examined. Genetic analysis of the MG_149 promoter indicates that the -10 region is essential for promoter activity whereas the -35 region is not. Further, the osmoinduction of MG_149 was shown to be regulated by DNA supercoiling, as evidenced by: 1) the dose-dependent reduction of MG_149 in the presence of novobiocin; 2) the parallel patterns of expression of MG_122 (topA), a gene known to be transcriptionally sensitive to DNA supercoiling changes; 3) the rapid response of MG_149 to NaCl alone or NaCl and novobiocin; 4) the presence of Stress Induced Duplex Destabilization (SIDD) profile in the promoter region. Together, these results indicate that DNA supercoiling regulates the osmoinduction of MG_149. It is proposed that DNA supercoiling may represent an appealing mechanism for transcription regulation in M. genitalium and other mycoplasmas in response to environmental changes. |
