Svensäter Gunnel, Sjögreen Bodil, Hamilton Ian R
Department of Oral Microbiology, Malmö University, S-21421 Malmö, Sweden1.
Department of Oral Biology, University of Manitoba, 780 Bannatyne Ave, Winnipeg, Manitoba, Canada R3E 0W22.
Microbiology (Reading). 2000 Jan;146 ( Pt 1):107-117. doi: 10.1099/00221287-146-1-107.
The authors have previously demonstrated that Streptococcus mutans shows an exponential-phase acid-tolerance response following an acid shock from pH 7.5 to 5.5 that enhances survival at pH 3.0. In this study the response of S. mutans H7 to acid shock was compared with the responses generated by salt, heat, oxidation and starvation. Prior induction of the acid-tolerance response did not cross-protect the cells from a subsequent challenge by the other stresses; however, prior adaptation to the other stresses, except heat (42 degrees C), protected the cells during a subsequent acid challenge at pH 3.5. Starvation by fivefold dilution of the basal medium (BM) plus fivefold reduction of its glucose content increased the numbers of survivors 12-fold, whereas elimination of glucose from fivefold-diluted BM led to a sevenfold enhancement compared to the control cells; this indicated a relationship between the acid and starvation responses. The stress responses were further characterized by comparing the 2D electrophoretic protein profiles of exponential-phase cells subjected to the various stress conditions. Cells were grown to exponential phase at pH 7.5 (37 degrees C) and then incubated for 30 min under the various stress conditions in the presence of 14C-labelled amino acids followed by cell extraction, protein separation by 2D gel electrophoresis and image analysis of the resulting autoradiograms. Using consistent twofold or greater changes in IOD % as a measure, oxidative stress resulted in the upregulation of 69 proteins, 15 of which were oxidation-specific, and in the downregulation of 24 proteins, when compared to the control cells. An acid shock from pH 7.5 to 5.5 enhanced synthesis of 64 proteins, 25 of them acid-specific, while 49 proteins exhibited diminished synthesis. The dilution of BM resulted in the increased formation of 58 proteins, with 11 starvation-specific proteins and 20 showing decreased synthesis. Some 52 and 40 proteins were enhanced by salt and heat stress, with 10 and 6 of these proteins, respectively, specific to the stress. The synthesis of a significant number of proteins was increased by more than one, but not all stress conditions; six proteins were enhanced by all five stress conditions and could be classified as general stress proteins. Clearly, the response of S. mutans to adverse environmental conditions results in complex and diverse alterations in protein synthesis to further cell survival.
作者们此前已经证明，变形链球菌在从pH 7.5至5.5的酸休克后会呈现指数期耐酸反应，这种反应可提高其在pH 3.0时的存活率。在本研究中，将变形链球菌H7对酸休克的反应与盐、热、氧化和饥饿所引发的反应进行了比较。预先诱导耐酸反应并不能使细胞免受随后其他应激的挑战；然而，预先适应其他应激（除42℃热应激外），可使细胞在随后pH 3.5的酸刺激中受到保护。通过将基础培养基（BM）稀释五倍并将其葡萄糖含量降低五倍来造成饥饿，可使存活菌数增加12倍，而从五倍稀释的BM中去除葡萄糖，与对照细胞相比，可使存活菌数增加7倍；这表明了酸反应与饥饿反应之间的关系。通过比较处于各种应激条件下的指数期细胞的二维电泳蛋白质谱，对这些应激反应进行了进一步表征。细胞在pH 7.5（37℃）下生长至指数期，然后在存在14C标记氨基酸的情况下，于各种应激条件下孵育30分钟，随后进行细胞提取、通过二维凝胶电泳进行蛋白质分离以及对所得放射自显影片进行图像分析。以IOD%中一致的两倍或更大变化作为衡量标准，与对照细胞相比，氧化应激导致69种蛋白质上调，其中15种是氧化特异性的，24种蛋白质下调。从pH 7.5至5.5的酸休克增强了64种蛋白质的合成，其中25种是酸特异性的，而49种蛋白质的合成减少。BM的稀释导致58种蛋白质的形成增加，其中11种是饥饿特异性蛋白质，20种蛋白质合成减少。盐和热应激分别增强了约52种和40种蛋白质，其中分别有10种和6种蛋白质是应激特异性的。大量蛋白质的合成因不止一种但并非所有应激条件而增加；6种蛋白质在所有5种应激条件下均增强，可归类为一般应激蛋白。显然，变形链球菌对不利环境条件的反应导致蛋白质合成发生复杂多样的改变，以促进细胞存活。
