Division of Infectious Diseases, Department of Pediatrics, Center for Antimicrobial Resistance and Microbial Genomics, McGovern Medical School, University of Texas Health Sciences Center at Houston, Houston, Texas, USA.
Department of Infectious Diseases, MD Anderson Cancer Center, Houston, Texas, USA.
Infect Immun. 2021 Oct 15;89(11):e0021521. doi: 10.1128/IAI.00215-21. Epub 2021 Aug 9.
The mechanisms by which bacteria sense the host environment and alter gene expression are poorly understood. LiaFSR is a gene regulatory system unique to Gram-positive bacteria, including group A Streptococcus (GAS), and responds to cell envelope stress. We previously showed that LiaF acts as an inhibitor to LiaFSR activation in GAS. To better understand gene regulation associated with LiaFSR activation, we performed RNA sequencing on isogenic deletion mutants fixed in a LiaFSR "always on" (Δ) or "always off" (Δ) state. Transcriptome analyses of Δ and Δ in GAS showed near perfect inverse correlation, including the gene encoding the global transcriptional regulator SpxA2. In addition, mutant transcriptomes included genes encoding multiple virulence factors and showed substantial overlap with the CovRS regulon. Chromatin immunoprecipitation quantitative PCR demonstrated direct gene regulation following activation of the response regulator, LiaR. High SpxA2 levels as a result of LiaFSR activation were directly correlated with increased CovR-regulated virulence gene transcription. Furthermore, consistent with known virulence gene repression by phosphorylated CovR, elevated SpxA2 levels were inversely correlated with CovR phosphorylation. Despite increased transcription of several virulence factors, Δ (high SpxA2) exhibited a paradoxical virulence phenotype in both mouse and human blood models of disease. Likewise, despite decreased virulence factor transcription with Δ (low SpxA2), increased virulence was observed in an mouse model of disease-a phenotype attributable, in part, to known SpxA2-associated transcription. Our findings provide evidence of a critical role of LiaFSR in sensing the host environment and suggest a potential mechanism for gene regulatory system cross talk shared by many Gram-positive pathogens.
细菌感知宿主环境并改变基因表达的机制尚不清楚。 LiaFSR 是一种独特的革兰氏阳性菌（包括 A 组链球菌（GAS））的基因调控系统，对细胞包膜应激作出反应。我们之前表明 LiaF 作为 GAS 中 LiaFSR 激活的抑制剂。为了更好地理解与 LiaFSR 激活相关的基因调控，我们对固定在 LiaFSR“始终开启”（Δ）或“始终关闭”（Δ）状态的同基因缺失突变体进行了 RNA 测序。GAS 中 Δ 和 Δ 的转录组分析显示近乎完美的反向相关，包括编码全局转录调节剂 SpxA2 的基因。此外，突变体转录组包括编码多种毒力因子的基因，并与 CovRS 调控子有很大的重叠。染色质免疫沉淀定量 PCR 表明，响应调节剂 LiaR 的激活后，直接进行基因调控。由于 LiaFSR 激活导致的高 SpxA2 水平与增加的 CovR 调节的毒力基因转录直接相关。此外，与已知的由磷酸化 CovR 抑制的毒力基因一致，SpxA2 水平的升高与 CovR 磷酸化呈负相关。尽管一些毒力因子的转录增加，但 Δ（高 SpxA2）在疾病的小鼠和人血液模型中表现出矛盾的毒力表型。同样，尽管 Δ（低 SpxA2）的毒力因子转录减少，但在疾病的小鼠模型中观察到增加的毒力，这部分归因于已知的 SpxA2 相关转录。我们的发现提供了 LiaFSR 在感知宿主环境中的关键作用的证据，并表明了许多革兰氏阳性病原体共享的基因调控系统串扰的潜在机制。
