Svensäter G, Björnsson O, Hamilton I R
Department of Oral Biology, Centre for Oral Health Sciences, Malmö University, Malmö, Sweden.
Microbiology (Reading). 2001 Nov;147(Pt 11):2971-9. doi: 10.1099/00221287-147-11-2971.
Previous research with Streptococcus mutans and other oral streptococci has demonstrated that the acid shock of exponential-phase cells (pH 7.5 to 5.5) resulted in the induction of an acid tolerance response (ATR) increasing survival at low pH (3.5-3.0). The current study was designed to determine whether two fresh isolates, H7 and BM71, and two laboratory strains, Ingbritt and LT11, were capable of a stationary-phase ATR as estimated by a survival test at pH 3.5 for 3 h. All four strains were unable to generate a stationary-phase ATR under control conditions at pH 7.5, with the exception of a burst of survivors in the transition between the exponential and stationary phases when the carbon source (glucose) was depleted. Adaptation at pH 5.5 resulted in the expected pH-dependent exponential-phase ATR, but only the fresh isolates exhibited a stationary-phase ATR at this pH. Glucose starvation of cells in complex medium was shown to enhance acid tolerance for the fresh isolates, but not the laboratory strains. This tolerance was, however, greatly diminished for all strains in a defined medium with a low concentration of amino acids. Growth of strain H7 in complex medium resulted in the formation of at least 56 extracellular proteins, nine of which were degraded in the early stationary phase following the induction of proteolytic activity during the transition period. No proteolytic activity was observed with strain LT11 and only 19 extracellular proteins/peptides were apparent in the medium with only one being degraded in the early stationary phase. Strain H7 was also shown to have two- to fourfold higher levels of intracellular glycogen in the stationary phase than strain LT11. These results suggest that S. mutans H7 possessed the required endogenous metabolism to support amino acid/peptide uptake in the early-stationary phase, which resulted in the formation of basic end products that, in turn, contributed to enhanced intracellular pH homeostasis.
先前对变形链球菌和其他口腔链球菌的研究表明，指数生长期细胞（pH 7.5至5.5）的酸休克会诱导酸耐受反应（ATR），从而提高在低pH值（3.5 - 3.0）下的存活率。当前的研究旨在确定两种新分离株H7和BM71以及两种实验室菌株Ingbritt和LT11是否能够通过在pH 3.5下进行3小时的存活试验来评估其稳定期ATR。在pH 7.5的对照条件下，所有四种菌株均无法产生稳定期ATR，但当碳源（葡萄糖）耗尽时，在指数期和稳定期过渡阶段会出现一阵存活菌。在pH 5.5下进行适应会导致预期的pH依赖性指数期ATR，但只有新分离株在该pH值下表现出稳定期ATR。在复杂培养基中对细胞进行葡萄糖饥饿处理可增强新分离株的耐酸性，但对实验室菌株则无此作用。然而，在氨基酸浓度较低的限定培养基中，所有菌株的这种耐受性都大大降低。菌株H7在复杂培养基中的生长导致至少形成56种细胞外蛋白质，其中9种在过渡期诱导蛋白水解活性后在稳定期早期被降解。在菌株LT11中未观察到蛋白水解活性，并且在培养基中仅出现19种细胞外蛋白质/肽，其中只有一种在稳定期早期被降解。还显示菌株H7在稳定期的细胞内糖原水平比菌株LT11高两到四倍。这些结果表明，变形链球菌H7具有支持稳定期早期氨基酸/肽摄取所需的内源性代谢，这导致形成碱性终产物，进而有助于增强细胞内pH稳态。
