Sturr M G, Guffanti A A, Krulwich T A
Department of Biochemistry, Mount Sinai School of Medicine, City University of New York, New York 10029.
J Bacteriol. 1994 Jun;176(11):3111-6. doi: 10.1128/jb.176.11.3111-3116.1994.
The effect of external pH on growth of alkaliphilic Bacillus firmus OF4 was studied in steady-state, pH-controlled cultures at various pH values. Generation times of 54 and 38 min were observed at external pH values of 7.5 and 10.6, respectively. At more alkaline pH values, generation times increased, reaching 690 min at pH 11.4; this was approximately the upper limit of pH for growth with doubling times below 12 h. Decreasing growth rates above pH 11 correlated with an apparent decrease in the ability to tightly regulate cytoplasmic pH and with the appearance of chains of cells. Whereas the cytoplasmic pH was maintained at pH 8.3 or below up to external pH values of 10.8, there was an increase up to pH 8.9 and 9.6 as the growth pH was increased to 11.2 and 11.4, respectively. Both the transmembrane electrical potential and the phosphorylation potential (delta Gp) generally increased over the total pH range, except for a modest fall-off in the delta Gp at pH 11.4. The capacity for pH homeostasis rather than that for oxidative phosphorylation first appeared to become limiting for growth at the high edge of the pH range. No cytoplasmic or membrane-associated organelles were observed at any growth pH, confirming earlier conclusions that structural sequestration of oxidative phosphorylation was not used to resolve the discordance between the total electrochemical proton gradient (delta p) and the delta Gp as the external pH is raised. Were a strictly bulk chemiosmotic coupling mechanism to account for oxidative phosphorylation over the entire range, the deltaGp/deltap ration (which would equal the H+/ATP ratio) would rise from about 3 at pH 7.5 to 13 at pH 11.2, dropping to 7 at pH 11.4 only because of the rise in cytoplasmic pH relative to other parameters. Moreover, the molar growth yields on malate were higher at pH 10.5 than at pH 7.5, indicating greater rather than lesser efficiency in the use of substrate at the more alkaline pH.
在不同pH值的稳态、pH控制培养条件下，研究了外部pH对嗜碱坚强芽孢杆菌OF4生长的影响。在外部pH值为7.5和10.6时，观察到的世代时间分别为54分钟和38分钟。在更高的碱性pH值下，世代时间增加，在pH 11.4时达到690分钟；这大约是生长的pH上限，倍增时间低于12小时。pH高于11时生长速率下降与紧密调节细胞质pH的能力明显下降以及细胞链的出现有关。在外部pH值达到10.8之前，细胞质pH维持在8.3或更低，随着生长pH分别增加到11.2和11.4，细胞质pH分别增加到8.9和9.6。除了在pH 11.4时磷酸化电位（ΔGp）略有下降外，跨膜电位和磷酸化电位（ΔGp）在整个pH范围内总体上都增加。在pH范围的上限，pH稳态能力而非氧化磷酸化能力似乎首先成为生长的限制因素。在任何生长pH下均未观察到细胞质或膜相关细胞器，这证实了早期的结论，即随着外部pH升高，氧化磷酸化的结构隔离并未用于解决总电化学质子梯度（Δp）和ΔGp之间的不一致。如果严格的整体化学渗透偶联机制在整个范围内解释氧化磷酸化，那么ΔGp/Δp比值（等于H⁺/ATP比值）将从pH 7.5时的约3上升到pH 11.2时的13，仅由于细胞质pH相对于其他参数的升高，在pH 11.4时降至7。此外，苹果酸的摩尔生长产率在pH 10.5时高于pH 7.5时，表明在更高的碱性pH下底物利用效率更高而非更低。
