Ahmer B M, van Reeuwijk J, Timmers C D, Valentine P J, Heffron F
Department of Molecular Microbiology and Immunology, Oregon Health Sciences University, Portland 97201-3098, USA.
J Bacteriol. 1998 Mar;180(5):1185-93. doi: 10.1128/JB.180.5.1185-1193.1998.
Quorum sensing is a phenomenon in which bacteria sense and respond to their own population density by releasing and sensing pheromones. In gram-negative bacteria, quorum sensing is often performed by the LuxR family of transcriptional regulators, which affect phenotypes as diverse as conjugation, bioluminescence, and virulence gene expression. The gene encoding one LuxR family member, named sdiA (suppressor of cell division inhibition), is present in the Escherichia coli genome. In this report, we have cloned the Salmonella typhimurium homolog of SdiA and performed a systematic screen for sdiA-regulated genes. A 4.4-kb fragment encoding the S. typhimurium sdiA gene was sequenced and found to encode the 3' end of YecC (homologous to amino acid transporters of the ABC family), all of SdiA and SirA (Salmonella invasion regulator), and the 5' end of UvrC. This gene organization is conserved between E. coli and S. typhimurium. We determined that the S. typhimurium sdiA gene was able to weakly complement the E. coli sdiA gene for activation of ftsQAZ at promoter 2 and for suppression of filamentation caused by an ftsZ(Ts) allele. To better understand the function of sdiA in S. typhimurium, we screened 10,000 random lacZY transcriptional fusions (MudJ transposon mutations) for regulation by sdiA. Ten positively regulated fusions were isolated. Seven of the fusions were within an apparent operon containing ORF8, ORF9, rck (resistance to complement killing), and ORF11 of the S. typhimurium virulence plasmid. The three ORFs have now been named srgA, srgB, and srgC (for sdiA-regulated gene), respectively. The DNA sequence adjacent to the remaining three fusions shared no similarity with previously described genes.
群体感应是一种细菌通过释放和感知信息素从而感知自身种群密度并做出反应的现象。在革兰氏阴性菌中，群体感应通常由LuxR家族的转录调节因子来执行，这些调节因子会影响诸如接合、生物发光和毒力基因表达等多种表型。编码一种名为sdiA（细胞分裂抑制抑制因子）的LuxR家族成员的基因存在于大肠杆菌基因组中。在本报告中，我们克隆了鼠伤寒沙门氏菌的sdiA同源物，并对sdiA调控的基因进行了系统筛选。对一个编码鼠伤寒沙门氏菌sdiA基因的4.4 kb片段进行了测序，发现它编码YecC（与ABC家族的氨基酸转运体同源）的3'端、整个SdiA和SirA（鼠伤寒沙门氏菌侵袭调节因子）以及UvrC的5'端。这种基因组织在大肠杆菌和鼠伤寒沙门氏菌之间是保守的。我们确定鼠伤寒沙门氏菌的sdiA基因能够在一定程度上互补大肠杆菌的sdiA基因，从而激活启动子2处的ftsQAZ，并抑制由ftsZ（Ts）等位基因引起的丝状化。为了更好地理解sdiA在鼠伤寒沙门氏菌中的功能，我们筛选了10000个随机的lacZY转录融合体（MudJ转座子突变体），以检测其是否受sdiA调控。分离出了10个正向调控的融合体。其中7个融合体位于一个明显的操纵子内，该操纵子包含鼠伤寒沙门氏菌毒力质粒的ORF8、ORF9、rck（抗补体杀伤）和ORF11。现在这三个ORF分别被命名为srgA、srgB和srgC（代表sdiA调控基因）。其余三个融合体附近的DNA序列与先前描述的基因没有相似性。
