Mercade M, Cocaign-Bousquet M, Loubière P
Laboratoire de Biotechnologie-Bioprocédés, Institut National des Sciences Appliquées, UMR INSA/CNRS 5504 & UMR INSA/INKA 792 Toulouse Cedex 4, France.
J Appl Microbiol. 2006 Jun;100(6):1364-72. doi: 10.1111/j.1365-2672.2006.02867.x.
To analyse the phenotype of a relA acid-resistant mutant of Lactococcus lactis ssp. cremoris MG1363, and to compare the glyceraldehyde-3-phosphate dehydrogenase regulation in both strains.
Lactococcus lactis ssp. cremoris MG1363 and the relA mutant affected in the (p)ppGpp synthetase were grown in a series of batch-mode fermentation at different pH-regulated conditions with glucose as carbon substrate. All the determinants of the glyceraldehyde-3-phosphate dehydrogenase (GAPDH) regulation were quantified. In L. lactis MG1363, the GAPDH was strongly inhibited in vitro by decreased pH values, but this inhibition was totally compensated in vivo by the lower NADH/NAD+ ratio and more efficiently by the important increase in the intracellular amount of GAPDH. In contrast to the wild type, GAPDH activity of the relA strain was not increased when grown at low pH but the level of GAPDH remained constitutively high. However, pH homeostasis was not improved in the relA mutant and it grew slower and exhibited a lower glycolytic flux than the wild-type strain at low pH.
Despite a better resistance to acid stress, the increased survival in L. lactis relA mutant at low pH was not related with an improved pH homeostasis but was associated with a diminished capacity to maintain a high flux through glycolysis.
The phenotype of a strong acid-resistant L. lactis strain was established in acid conditions and some key metabolic parameters compared with the wild type. This analysis led to the conclusion that growth and survival seem to be antinomic parameters, since improving one of them leads to a decrease in the other one.
分析乳酸乳球菌乳脂亚种MG1363的relA耐酸突变体的表型，并比较两株菌中甘油醛-3-磷酸脱氢酶的调控情况。
将乳酸乳球菌乳脂亚种MG1363和在（p）ppGpp合成酶方面有缺陷的relA突变体，在以葡萄糖为碳源底物、不同pH调控条件下进行一系列分批式发酵培养。对甘油醛-3-磷酸脱氢酶（GAPDH）调控的所有决定因素进行了定量分析。在乳酸乳球菌MG1363中，体外实验表明GAPDH活性受pH值降低的强烈抑制，但在体内较低的NADH/NAD⁺比值可完全补偿这种抑制作用，而细胞内GAPDH含量的显著增加能更有效地补偿。与野生型不同，relA菌株在低pH条件下生长时GAPDH活性并未增加，但其GAPDH水平持续保持较高。然而，relA突变体的pH稳态并未改善，在低pH条件下其生长较慢且糖酵解通量低于野生型菌株。
尽管乳酸乳球菌relA突变体对酸胁迫具有更好的抗性，但其在低pH条件下存活率的提高与pH稳态的改善无关，而是与维持较高糖酵解通量的能力降低有关。
在酸性条件下确定了一株强酸抗性乳酸乳球菌菌株的表型，并与野生型比较了一些关键代谢参数。该分析得出结论：生长和存活似乎是相互矛盾的参数，因为改善其中一个会导致另一个下降。
