Departamento de Genética, Facultad de Biología, Universidad de Sevilla, Seville, Spain.
Genetics. 2010 Apr;184(4):947-58. doi: 10.1534/genetics.109.109918. Epub 2010 Jan 18.
The virulence plasmid of Salmonella enterica (pSLT) is an F-like conjugative plasmid. High rates of pSLT transfer occur in the mammalian gut, a microaerobic environment. In this study, we describe genetic screens for host-encoded activators and repressors of the transfer operon (tra) of pSLT. We show that the transcription factor ArcA is an activator of conjugation, especially under microaerobiosis. In turn, succinate dehydrogenase (SdhABCD) is a repressor of mating in aerobiosis. ArcA binds upstream of the main tra promoter (p(traY)) and activates tra transcription, as previously described in F, R1, and R100. In the absence of ArcA, transfer of pSLT decreased 7-fold in aerobiosis and >100-fold in microaerobiosis. In aerobiosis, ArcA activates the traY promoter in an ArcB-independent manner, as described in other F-like plasmids. In microaerobiosis, however, the ArcB sensor is necessary for activation of p(traY). Lack of Sdh causes a >20-fold increase in pSLT transfer in aerobiosis, but has little effect under microaerobiosis. Sdh inhibits conjugal transfer by reducing traJ transcription, probably in an indirect manner. In turn, the sdhCDAB operon is repressed by the ArcAB system under microaerobiosis. Hence, the ArcAB two-component system of S. enterica stimulates pSLT transfer under microaerobiosis by two concerted actions: activation of the tra operon and repression of the sdhCDAB operon.
鼠伤寒沙门氏菌（Salmonella enterica）的毒力质粒（pSLT）是一种 F 型可接合质粒。在哺乳动物肠道中，pSLT 以很高的频率发生转移，而肠道是一个微需氧环境。在本研究中，我们描述了针对 pSLT 转移操纵子（tra）的宿主编码激活子和抑制剂的遗传筛选。我们发现转录因子 ArcA 是接合的激活子，特别是在微需氧条件下。相反，琥珀酸脱氢酶（SdhABCD）在需氧条件下是交配的抑制剂。ArcA 结合在主要 tra 启动子（p(traY))的上游，激活 tra 转录，如先前在 F、R1 和 R100 中所描述的。在没有 ArcA 的情况下，pSLT 在需氧条件下的转移减少了 7 倍，在微需氧条件下减少了 100 倍以上。在需氧条件下，ArcA 以与其他 F 型质粒中描述的方式独立于 ArcB 激活 traY 启动子。然而，在微需氧条件下，ArcB 传感器对于 p(traY)的激活是必要的。缺乏 Sdh 会导致 pSLT 在需氧条件下的转移增加 20 倍以上，但在微需氧条件下影响很小。Sdh 通过降低 traJ 转录抑制接合转移，可能是间接的。反过来，sdhCDAB 操纵子在微需氧条件下受到 ArcAB 系统的抑制。因此，鼠伤寒沙门氏菌的 ArcAB 双组分系统通过两种协同作用刺激 pSLT 在微需氧条件下的转移：tra 操纵子的激活和 sdhCDAB 操纵子的抑制。
