Department of Oral Biology, University of Florida, College of Dentistry, Gainesville, FL 32610, USA.
J Bacteriol. 2011 Feb;193(4):862-74. doi: 10.1128/JB.01257-10. Epub 2010 Dec 10.
Streptococcus mutans, a primary agent of dental caries, has three (p)ppGpp synthases: RelA, which is required for a mupirocin-induced stringent response; RelP, which produces (p)ppGpp during exponential growth and is regulated by the RelRS two-component system; and RelQ. Transcription of relPRS and a gene cluster (SMu0835 to SMu0837) located immediately upstream was activated in cells grown with aeration and during a stringent response, respectively. Bioinformatic analysis predicted that SMu0836 and SMu0837 encode ABC exporters, which we designated rcrPQ (rel competence-related) genes, respectively. SMu0835 (rcrR) encodes a MarR family transcriptional regulator. Reverse transcriptase PCR (RT-PCR) and quantitative RT-PCR analysis showed that RcrR functions as an autogenous negative regulator of the expression of the rcrRPQ operon. A mutant in which a polar insertion replaced the SMu836 gene (Δ836polar) grew more slowly and had final yields that were lower than those of the wild-type strain. Likewise, the Δ836polar strain had an impaired capacity to form biofilms, grew poorly at pH 5.5, and was more sensitive to oxidative stressors. Optimal expression of rcrPQ required RelP and vice versa. Replacement of rcrR with a nonpolar antibiotic resistance marker (Δ835np), which leads to overexpression of rcrPQ, yielded a strain that was not transformable with exogenous DNA. Transcriptional analysis revealed that the expression of comYA and comX was dramatically altered in the Δ835np and Δ836polar mutants. Collectively, the data support the suggestion that the rcrRPQ gene products play a critical role in physiologic homeostasis and stress tolerance by linking (p)ppGpp metabolism, acid and oxidative stress tolerance, and genetic competence.
变形链球菌是龋齿的主要病原体，它有三种（p）ppGpp 合酶：RelA，它是 mupirocin 诱导严格反应所必需的；RelP，在指数生长期产生（p）ppGpp，受 RelRS 双组分系统调节；和 RelQ。当细胞在通气和严格反应条件下生长时，relPRS 和位于其上游的基因簇（SMu0835 到 SMu0837）的转录分别被激活。生物信息学分析预测，SMu0836 和 SMu0837 分别编码 ABC 外排泵，我们将其分别命名为 rcrPQ（与竞争相关的基因）。SMu0835（rcrR）编码 MarR 家族转录调节剂。逆转录 PCR（RT-PCR）和定量 RT-PCR 分析表明，RcrR 作为 rcrRPQ 操纵子表达的自体负调控因子。一个在 SMu836 基因处发生极性插入的突变体（Δ836polar）生长更缓慢，最终产量低于野生型菌株。同样，Δ836polar 菌株形成生物膜的能力受损，在 pH 5.5 下生长不良，并且对氧化应激剂更敏感。rcrPQ 的最佳表达需要 RelP，反之亦然。用非极性抗生素抗性标记（Δ835np）取代 rcrR，导致 rcrPQ 过表达，得到的菌株不能转化外源 DNA。转录分析表明，Δ835np 和 Δ836polar 突变体中 comYA 和 comX 的表达发生了显著改变。总的来说，这些数据支持以下观点，即 rcrRPQ 基因产物通过连接（p）ppGpp 代谢、酸和氧化应激耐受以及遗传竞争力，在生理动态平衡和应激耐受中发挥关键作用。
