Departamento de Bioquímica y Biología Molecular y Genética, Facultad de Veterinaria, Universidad de Extremadura, 10003 Cáceres, Spain.
BioMic Research Group, Meat and Meat Products Research Institute (IProCar), Universidad de Extremadura, 10004 Cáceres, Spain.
Genes (Basel). 2020 Oct 30;11(11):1292. doi: 10.3390/genes11111292.
The effect of initial pH on bacterial cell-growth and its change over time was studied under aerobic heterotrophic conditions by using three bacterial strains: ATCC 25922, KT2440, and CECT 5344. In Luria-Bertani (LB) media, pH evolved by converging to a certain value that is specific for each bacterium. By contrast, in the buffered Minimal Medium (MM), pH was generally more stable along the growth curve. In MM with glucose as carbon source, a slight acidification of the medium was observed for all strains. In the case of , a sudden drop in pH was observed during exponential cell growth that was later recovered at initial pH 7 or 8, but was irreversible below pH 6, thus arresting further cell-growth. When using other carbon sources in MM at a fixed initial pH, pH changes depended mainly on the carbon source itself. While glucose, glycerol, or octanoate slightly decreased extracellular pH, more oxidized carbon sources, such as citrate, 2-furoate, 2-oxoglutarate, and fumarate, ended up with the alkalinization of the medium. These observations are in accordance with pH change predictions using genome-scale metabolic models for the three strains, thus revealing the metabolic reasons behind pH change. Therefore, we conclude that the composition of the medium, specifically the carbon source, determines pH change during bacterial growth to a great extent and unravel the main molecular mechanism behind this phenotype. These findings pave the way for predicting pH changes in a given bacterial culture and may anticipate the interspecies interactions and fitness of bacteria in their environment.
本研究采用三种细菌菌株（ATCC 25922、KT2440 和 CECT 5344），在需氧异养条件下研究初始 pH 值对细菌细胞生长及其随时间变化的影响。在 Luria-Bertani (LB) 培养基中，pH 值通过收敛到特定于每种细菌的特定值而演变。相比之下，在缓冲的最小培养基 (MM) 中，pH 值通常在生长曲线中更稳定。在以葡萄糖为碳源的 MM 中，所有菌株的培养基都观察到轻微酸化。对于菌株 ，在指数期细胞生长过程中观察到 pH 值突然下降，随后在初始 pH 值 7 或 8 下恢复，但在 pH 值低于 6 时不可逆，从而阻止进一步的细胞生长。当在固定初始 pH 值的 MM 中使用其他碳源时，pH 值变化主要取决于碳源本身。虽然葡萄糖、甘油或辛酸略微降低了细胞外 pH 值，但更氧化的碳源，如柠檬酸、2-呋喃酸、2-氧戊二酸和富马酸，最终使培养基碱化。这些观察结果与使用三种菌株的基因组规模代谢模型对 pH 值变化的预测一致，从而揭示了 pH 值变化背后的代谢原因。因此，我们得出结论，培养基的组成，特别是碳源，在很大程度上决定了细菌生长过程中的 pH 值变化，并揭示了这种表型背后的主要分子机制。这些发现为预测给定细菌培养物中的 pH 值变化铺平了道路，并可能预测细菌在其环境中的种间相互作用和适应性。
