Center for Oral Biology, University of Rochester School of Medicine and Dentistry, Rochester, New York, USA.
J Bacteriol. 2012 Apr;194(8):2010-9. doi: 10.1128/JB.06737-11. Epub 2012 Feb 10.
The ability of Streptococcus mutans to produce and tolerate organic acids from carbohydrate metabolism represents a major virulence factor responsible for the formation of carious lesions. Pyruvate is a key metabolic intermediate that, when rerouted to other metabolic pathways such as amino acid biosynthesis, results in the alleviation of acid stress by reducing acid end products and aiding in maintenance of intracellular pH. Amino acid biosynthetic genes such as ilvC and ilvE were identified as being upregulated in a proteome analysis of Streptococcus mutans under acid stress conditions (A. C. Len, D. W. Harty, and N. A. Jacques, Microbiology 150:1353-1366, 2004). In Lactococcus lactis and Staphylococcus carnosus, the ilvE gene product is involved with biosynthesis and degradation of branched-chain amino acids, as well as in the production of branched-chain fatty acids (B. Ganesan and B. C. Weimer, Appl. Environ. Microbiol. 70:638-641, 2004; S. M. Madsen et al., Appl. Environ. Microbiol. 68:4007-4014, 2002; and M. Yvon, S. Thirouin, L. Rijnen, D. Fromentier, and J. C. Gripon, Appl. Environ. Microbiol. 63:414-419, 1997). Here we constructed and characterized an ilvE deletion mutant of S. mutans UA159. Growth experiments revealed that the ilvE mutant strain has a lag in growth when nutritionally limited for branched-chain amino acids. We further demonstrated that the loss of ilvE causes a decrease in acid tolerance. The ilvE strain exhibits a defect in F(1)-F(o) ATPase activity and has reduced catabolic activity for isoleucine and valine. Results from transcriptional studies showed that the ilvE promoter is upregulated during growth at low pH. Collectively, the results of this investigation show that amino acid metabolism is a component of the acid-adaptive repertoire of S. mutans.
变形链球菌产生和耐受碳水化合物代谢产生的有机酸的能力是导致龋齿形成的主要毒力因子。丙酮酸是一种关键的代谢中间产物，当它被重新定向到其他代谢途径，如氨基酸生物合成途径时，通过减少酸的终产物并有助于维持细胞内 pH 值，从而减轻酸应激。在酸胁迫条件下对变形链球菌的蛋白质组分析中，鉴定出丙氨酸生物合成基因如 ilvC 和 ilvE 上调（A. C. Len、D. W. Harty 和 N. A. Jacques， Microbiology 150:1353-1366, 2004）。在乳球菌和肉葡萄球菌中，ilvE 基因产物参与支链氨基酸的生物合成和降解，以及支链脂肪酸的产生（B. Ganesan 和 B. C. Weimer， Appl. Environ. Microbiol. 70:638-641, 2004；S. M. Madsen 等人， Appl. Environ. Microbiol. 68:4007-4014, 2002；和 M. Yvon、S. Thirouin、L. Rijnen、D. Fromentier 和 J. C. Gripon， Appl. Environ. Microbiol. 63:414-419, 1997）。在这里，我们构建并表征了变形链球菌 UA159 的 ilvE 缺失突变株。生长实验表明，当营养受到支链氨基酸限制时，ilvE 突变株的生长有一个延迟。我们进一步证明，缺失 ilvE 会导致耐酸能力下降。ilvE 菌株的 F(1)-F(o)ATP 酶活性降低，对异亮氨酸和缬氨酸的分解代谢活性降低。转录研究的结果表明，ilvE 启动子在低 pH 值下生长时上调。总的来说，这项研究的结果表明，氨基酸代谢是变形链球菌酸适应谱的一个组成部分。
