Key Laboratory of Genome Sciences and Information, Beijing Institute of Genomics, Chinese Academy of Sciences, Beijing, China.
Graduate Institute of Biomedical Sciences, College of Medicine, Chang Gung University, Taoyuan, Taiwan.
BMC Genomics. 2018 May 23;19(1):386. doi: 10.1186/s12864-018-4781-z.
Streptococcus salivarius is an abundant isolate of the human oral microbiota. Since both pH and glucose availability fluctuate frequently in the oral cavity, the goal of this study was to investigate regulation by CodY, a conserved pleiotropic regulator of Gram positive bacteria, in response to these two signals. The chemostat culture system was employed to precisely control the growth parameters, and the transcriptomes of wild-type S. salivarius 57.I and its CodY-null derivative (ΔcodY) grown at pH 7 and 5.5, with limited and excessive glucose supply were determined.
The transcriptomic analysis revealed that CodY was most active at pH 7 under conditions of glucose limitation. Based on whether a CodY binding consensus could be located in the 5' flanking region of the identified target, the transcriptomic analysis also found that CodY shaped the transcriptome via both direct and indirect regulation. Inactivation of codY reduced the glycolytic capacity and the viability of S. salivarius at pH 5.5 or in the presence of HO. Studies using the Galleria mellonella larva model showed that CodY was essential for the toxicity generated from S. salivarius infection, suggesting that CodY regulation was critical for immune evasion and systemic infections. Furthermore, the CodY-null mutant strain exhibited a clumping phenotype and reduced attachment in biofilm assays, suggesting that CodY also modulates cell wall metabolism. Finally, the expression of genes belonging to the CovR regulon was affected by codY inactivation, but CodY and CovR regulated these genes in opposite directions.
Metabolic adaptation in response to nutrient availability and growth pH is tightly linked to stress responses and virulence expression in S. salivarius. The regulation of metabolism by CodY allows for the maximal utilization of available nutrients and ATP production. The counteractive regulation of the CovR regulon could fine tune the transcriptomes in response to environmental changes.
唾液链球菌是人类口腔微生物群中丰富的分离株。由于口腔中的 pH 值和葡萄糖供应经常波动，因此本研究的目的是研究 CodY（一种革兰氏阳性细菌的保守多效调节因子）对这两个信号的响应调节。恒化器培养系统用于精确控制生长参数，并且确定了在 pH 值为 7 和 5.5 下，在有限和过量葡萄糖供应下，野生型 S. salivarius 57.I 及其 CodY 缺失突变体（Δ codY）的转录组。
转录组分析表明，CodY 在葡萄糖限制条件下 pH 值为 7 时最活跃。根据是否可以在鉴定的靶标 5'侧翼区域找到 CodY 结合共识，转录组分析还发现 CodY 通过直接和间接调节来塑造转录组。codY 的失活降低了 S. salivarius 在 pH 值为 5.5 或存在 HO 时的糖酵解能力和活力。使用 Galleria mellonella 幼虫模型的研究表明，CodY 对于 S. salivarius 感染产生的毒性是必不可少的，这表明 CodY 调节对于免疫逃避和全身感染至关重要。此外，CodY 缺失突变株在生物膜测定中表现出聚集表型和附着减少，表明 CodY 还调节细胞壁代谢。最后，CovR 调控子的基因表达受到 codY 失活的影响，但 CodY 和 CovR 以相反的方向调节这些基因。
对营养物质可用性和生长 pH 值的代谢适应与 S. salivarius 中的应激反应和毒力表达紧密相关。CodY 对代谢的调节允许最大程度地利用可用营养物质和产生 ATP。CovR 调控子的反向调节可以微调转录组以响应环境变化。
