Martín-Galiano Antonio J, Overweg Karin, Ferrándiz Maria J, Reuter Mark, Wells Jerry M, de la Campa Adela G
Unidad de Genética Bacteriana, Centro Nacional de Microbiología, Instituto de Salud Carlos III, 28220, Majadahonda, Madrid, Spain.
Bacterial Infection and Immunity Group, Institute of Food Research, Norwich Research Park, Norwich NR4 7UA, UK.
Microbiology (Reading). 2005 Dec;151(Pt 12):3935-3946. doi: 10.1099/mic.0.28238-0.
Streptococcus pneumoniae, one of the major causes of morbidity and mortality in humans, faces a range of potentially acidic conditions in the middle and late stages of growth in vitro, in diverse human fluids during the infection process, and in biofilms present in the nasopharynx of carriers. S. pneumoniae was shown to develop a weak acid tolerance response (ATR), where cells previously exposed to sublethal pHs (5.8-6.6) showed an increased survival rate of up to one order of magnitude after challenge at the lethal pH (4.4, survival rate of 10(-4)). Moreover, the survival after challenge of stationary phase cells at pH 4.4 was three orders of magnitude higher than that of cells taken from the exponential phase, due to the production of lactic acid during growth and increasing acidification of the growth medium until stationary phase. Global expression analysis after short-term (5, 15 and 30 min, the adaptation phase) and long-term (the maintenance phase) acidic shock (pH 6.0) was performed by microarray experiments, and the results were validated by real-time RT-PCR. Out of a total of 126 genes responding to acidification, 59 and 37 were specific to the adaptation phase and maintenance phase, respectively, and 30 were common to both periods. In the adaptation phase, both up- and down-regulation of gene transcripts was observed (38 and 21 genes, respectively), whereas in the maintenance phase most of the affected genes were down-regulated (34 out of 37). Genes involved in protein fate (including those involved in the protection of the protein native structure) and transport (including transporters of manganese and iron) were overrepresented among the genes affected by acidification, 8.7 and 24.6 % of the acid-responsive genes compared to 2.8 % and 9.6 % of the genome complement, respectively. Cross-regulation with the response to oxidative and osmotic stress was observed. Potential regulatory motifs involved in the ATR were identified in the promoter regions of some of the regulated genes.
肺炎链球菌是人类发病和死亡的主要原因之一，在体外生长的中晚期、感染过程中的各种人体体液以及携带者鼻咽部的生物膜中，它面临一系列潜在的酸性环境。研究表明，肺炎链球菌会产生弱酸耐受反应（ATR），即先前暴露于亚致死pH值（5.8 - 6.6）的细胞在致死pH值（4.4，存活率为10⁻⁴）下受到挑战后，存活率提高了一个数量级。此外，由于生长过程中产生乳酸以及生长培养基酸化程度不断增加直至稳定期，稳定期细胞在pH 4.4受到挑战后的存活率比指数期细胞高出三个数量级。通过微阵列实验对短期（5、15和30分钟，适应阶段）和长期（维持阶段）酸性休克（pH 6.0）后的全局表达进行了分析，并通过实时RT-PCR对结果进行了验证。在总共126个对酸化有反应的基因中，分别有59个和37个基因特定于适应阶段和维持阶段，30个基因在两个时期都有。在适应阶段，观察到基因转录本的上调和下调（分别为38个和21个基因），而在维持阶段，大多数受影响的基因被下调（37个中的34个）。参与蛋白质命运（包括参与保护蛋白质天然结构的那些）和运输（包括锰和铁的转运蛋白）的基因在受酸化影响的基因中占比过高，与基因组互补序列中的2.8%和9.6%相比，分别占酸反应基因的8.7%和24.6%。观察到与氧化应激和渗透压应激反应的交叉调节。在一些受调控基因的启动子区域中鉴定出了参与ATR的潜在调控基序。
