Smith Jenée N, Ahmer Brian M M
Department of Microbiology, The Ohio State University, Columbus Ohio 43210, USA.
J Bacteriol. 2003 Feb;185(4):1357-66. doi: 10.1128/JB.185.4.1357-1366.2003.
Salmonella, Escherichia, and Klebsiella do not encode any recognized type of N-acylhomoserine lactone (AHL) synthase, and consistent with this, they do not synthesize AHLs under any conditions tested. However, they do encode an AHL receptor of the LuxR family, named SdiA. MudJ fusions in four loci are known to respond to plasmid-encoded sdiA in Salmonella, but only the rck locus has been described. Here we report the location and sequence analysis of the remaining three loci. The srg-6::MudJ is within gtgA of the gifsy-2 prophage, and the srg-7::MudJ is within PSLT61 of the virulence plasmid. Both fusions are in the antisense orientation. The third fusion, srgE5::MudJ, is within a horizontally acquired gene of unknown function at 33.6 centisomes that we have named srgE. Previously, sdiA expressed from its natural position in the chromosome was demonstrated to activate a plasmid-based transcriptional fusion to the rck promoter in response to AHL production by other bacterial species. However, the MudJ fusions did not respond to chromosomal sdiA. Here we report that MudJ fusions to three of the four loci (not srg-6) are activated by AHL in an sdiA-dependent manner during growth in motility agar (0.25% agar) but not during growth in top agar (0.7% agar) or on agar plates (1.2% agar). In motility agar, the srgE promoter responds to sdiA at 30 degrees C and higher while the rck and srg-7 promoters respond only at 37 or 42 degrees C. Substantial AHL-independent SdiA activity was observed at 30 degrees C but not at 37 degrees C.
沙门氏菌、大肠杆菌和克雷伯氏菌不编码任何公认类型的N-酰基高丝氨酸内酯（AHL）合酶，与此一致的是，在任何测试条件下它们都不合成AHL。然而，它们确实编码一种LuxR家族的AHL受体，名为SdiA。已知沙门氏菌中四个位点的MudJ融合对质粒编码的sdiA有反应，但仅描述了rck位点。在此我们报告其余三个位点的定位和序列分析。srg-6::MudJ位于gifsy-2原噬菌体的gtgA内，srg-7::MudJ位于毒力质粒的PSLT61内。两种融合均为反义方向。第三个融合，srgE5::MudJ，位于33.6厘摩处一个功能未知的水平获得基因内，我们将其命名为srgE。先前已证明，从其在染色体上的天然位置表达的sdiA会响应其他细菌物种产生的AHL，激活与rck启动子的基于质粒的转录融合。然而，MudJ融合对染色体上的sdiA无反应。在此我们报告，在运动性琼脂（0.25%琼脂）中生长期间，四个位点中的三个（非srg-6）的MudJ融合以sdiA依赖的方式被AHL激活，但在顶层琼脂（0.7%琼脂）或琼脂平板（1.2%琼脂）中生长期间则不然。在运动性琼脂中，srgE启动子在30℃及更高温度下对sdiA有反应，而rck和srg-7启动子仅在37℃或42℃时有反应。在30℃时观察到大量不依赖AHL的SdiA活性，但在37℃时未观察到。
