Department of Microbiology and Cell Science, College of Agricultural and Life Sciences, University of Florida, Gainesville, FL 32611, USA.
BMC Microbiol. 2012 Sep 1;12:187. doi: 10.1186/1471-2180-12-187.
The S. mutans LrgA/B holin-like proteins have been shown to affect biofilm formation and oxidative stress tolerance, and are regulated by oxygenation, glucose levels, and by the LytST two-component system. In this study, we sought to determine if LytST was involved in regulating lrgAB expression in response to glucose and oxygenation in S. mutans.
Real-time PCR revealed that growth phase-dependent regulation of lrgAB expression in response to glucose metabolism is mediated by LytST under low-oxygen conditions. However, the effect of LytST on lrgAB expression was less pronounced when cells were grown with aeration. RNA expression profiles in the wild-type and lytS mutant strains were compared using microarrays in early exponential and late exponential phase cells. The expression of 40 and 136 genes in early-exponential and late exponential phase, respectively, was altered in the lytS mutant. Although expression of comYB, encoding a DNA binding-uptake protein, was substantially increased in the lytS mutant, this did not translate to an effect on competence. However, a lrgA mutant displayed a substantial decrease in transformation efficiency, suggestive of a previously-unknown link between LrgA and S. mutans competence development. Finally, increased expression of genes encoding antioxidant and DNA recombination/repair enzymes was observed in the lytS mutant, suggesting that the mutant may be subjected to increased oxidative stress during normal growth. Although the intracellular levels of reaction oxygen species (ROS) appeared similar between wild-type and lytS mutant strains after overnight growth, challenge of these strains with hydrogen peroxide (H2O2) resulted in increased intracellular ROS in the lytS mutant.
Overall, these results: (1) Reinforce the importance of LytST in governing lrgAB expression in response to glucose and oxygen, (2) Define a new role for LytST in global gene regulation and resistance to H2O2, and (3) Uncover a potential link between LrgAB and competence development in S. mutans.
变形链球菌 LrgA/B 孔样蛋白已被证实影响生物膜形成和氧化应激耐受性，且受氧分压、葡萄糖水平以及 LytST 双组分系统调控。本研究旨在确定 LytST 是否参与调控变形链球菌中 lrgAB 表达对葡萄糖和氧分压的应答。
实时 PCR 结果显示，在低氧条件下，LytST 通过调控糖代谢影响 lrgAB 表达的生长时相依赖性。然而，当细胞在有氧条件下生长时，LytST 对 lrgAB 表达的影响则不那么显著。通过比较野生型和 lytS 突变株在早期指数和晚期指数生长期的微阵列 RNA 表达谱，发现 lytS 突变株中 40 个和 136 个基因的表达分别发生改变。尽管 lytS 突变株中 comYB（编码 DNA 结合摄取蛋白）的表达显著增加，但这并没有转化为对感受态的影响。然而，lrgA 突变株的转化效率显著降低，提示 LrgA 与变形链球菌感受态发育之间存在以前未知的联系。最后，在 lytS 突变株中观察到抗氧化和 DNA 重组/修复酶编码基因的表达增加，表明该突变株在正常生长过程中可能受到更高的氧化应激。尽管野生型和 lytS 突变株在过夜生长后细胞内活性氧（ROS）水平相似，但用过氧化氢（H2O2）挑战这些菌株后，lytS 突变株的细胞内 ROS 增加。
总的来说，这些结果：（1）证实了 LytST 在调控葡萄糖和氧分压应答中 lrgAB 表达的重要性；（2）定义了 LytST 在全局基因调控和对 H2O2 抗性中的新作用；（3）揭示了 LrgAB 与变形链球菌感受态发育之间的潜在联系。
