Carlsson J, Hamilton I R
Department of Oral Microbiology, University of Umeå, Sweden.
Oral Microbiol Immunol. 1996 Dec;11(6):412-9. doi: 10.1111/j.1399-302x.1996.tb00204.x.
Experiments were conducted with Streptococcus mutans NCTC 10449 and Streptococcus sanguis ATCC 10556 to determine whether the acid end-products, lactate and acetate, were involved in the regulation of cellular growth and metabolism. The growth rate and culture biomass of both organisms was inhibited by the addition of lactate and acetate at concentrations as high as 200 mM to the cultures, although the final pH values of the lactate and acetate cultures were similar. In addition, the metabolic conversion of glucose to lactate was decreased by external lactate but stimulated by acetate. In spite of this, calculation of the yield of cell biomass per mole of ATP (YATP) showed that the yield of both organisms actually increased in the presence of added lactate, but decreased with acetate. This indicates that the two acids interacted with the cells of the organisms by different mechanisms. For both organisms, the final external undissociated lactic acid was relatively constant at concentrations between 0 and 200 mM added lactate, 24.9-32.5 mM for S. mutans and 8.0-11.5 mM for S. sanguis. On the other hand, the final concentration of undissociated acetic acid in the S. mutans cultures increased from 2.9 to 83.7 mM as the medium acetate concentration increased, and from 1.0 to 36.0 mM with the S. sanguis cultures. Counterflow experiments provided evidence for a lactate carrier in both S. mutans and S. sanguis, but an acetate carrier in these organisms could not be demonstrated. [14C]-lactate and [14C]-acetate were taken up into de-energized, chemostatgrown cells of S. mutans and S. sanguis in response to an artificially generated pH gradient but not by an imposed electrical gradient. Thus, under these conditions lactate uptake occurred via a symport process with only one proton. Growth of both organisms in the presence of increasing concentrations of acetate resulted in a small reduction (27%) in the transmembrane pH gradient (delta pH) as measured by the permeant acid, [14C]-salicylate. However, the uptake of [14C]-acetate for the estimation of delta pH revealed significant inhibition of the acetate concentration gradient in the presence external acetate, indicating that the cells expelled the acetate anion. The results indicate that, unlike acetate uptake, lactate transport by S. mutans and S. sanguis was strictly regulated via the lactate carrier in order to prevent excessive dissipation of the pH gradient. Clearly, the formation of acetate by oral streptococci is more problematic for cellular homeostasis than the formation of lactate.
使用变形链球菌NCTC 10449和血链球菌ATCC 10556进行实验，以确定酸性终产物乳酸和乙酸是否参与细胞生长和代谢的调节。向培养物中添加浓度高达200 mM的乳酸和乙酸会抑制这两种微生物的生长速率和培养物生物量，尽管乳酸和乙酸培养物的最终pH值相似。此外，外部乳酸会降低葡萄糖向乳酸的代谢转化，而乙酸则会刺激这种转化。尽管如此，每摩尔ATP的细胞生物量产率（YATP）计算表明，添加乳酸时两种微生物的产率实际上都增加了，但添加乙酸时产率却降低了。这表明这两种酸通过不同机制与微生物细胞相互作用。对于这两种微生物，添加乳酸浓度在0至200 mM之间时，最终外部未解离乳酸相对恒定，变形链球菌为24.9 - 32.5 mM，血链球菌为8.0 - 11.5 mM。另一方面，随着培养基中乙酸浓度增加，变形链球菌培养物中未解离乙酸的最终浓度从2.9 mM增加到83.7 mM，血链球菌培养物中则从1.0 mM增加到36.0 mM。逆流实验为变形链球菌和血链球菌中存在乳酸载体提供了证据，但未证明这些微生物中存在乙酸载体。[¹⁴C] - 乳酸和[¹⁴C] - 乙酸会响应人工产生的pH梯度而被摄取到变形链球菌和血链球菌的去能恒化器培养细胞中，但不会因施加的电势梯度而被摄取。因此，在这些条件下，乳酸摄取是通过仅与一个质子的同向转运过程发生的。在乙酸浓度不断增加的情况下培养这两种微生物，会导致通过渗透性酸[¹⁴C] - 水杨酸盐测量的跨膜pH梯度（ΔpH）略有降低（27%）。然而，用于估计ΔpH的[¹⁴C] - 乙酸摄取显示，在存在外部乙酸的情况下，乙酸浓度梯度受到显著抑制，表明细胞排出了乙酸阴离子。结果表明，与乙酸摄取不同，变形链球菌和血链球菌的乳酸转运通过乳酸载体受到严格调节，以防止pH梯度过度耗散。显然，口腔链球菌形成乙酸对细胞内稳态而言比形成乳酸更成问题。
