Department of Microbiology, Boston University School of Medicine, Boston, Massachusetts 02118.
Appl Environ Microbiol. 1986 Jul;52(1):86-91. doi: 10.1128/aem.52.1.86-91.1986.
We investigated the intracellular physiological conditions associated with the induction of butanol-producing enzymes in Clostridium acetobutylicum. During the acidogenic phase of growth, the internal pH decreased in parallel with the decrease in the external pH, but the internal pH did not go below 5.5 throughout batch growth. Butanol was found to dissipate the proton motive force of fermenting C. acetobutylicum cells by decreasing the transmembrane pH gradient, whereas the membrane potential was affected only slightly. In growing cells, the switch from acid to solvent production occurred when the internal undissociated butyric acid concentration reached 13 mM and the total intracellular undissociated acid concentration (acetic plus butyric acids) was at least 40 to 45 mM. Similar values were obtained when cultures were supplemented with 50 mM butyric acid initially or when a phosphate-buffered medium was used instead of an acetate-buffered medium. To measure the induction of the enzymes involved in solvent synthesis, we determined the rates of conversion of butyrate to butanol in growing cells. The rate of butanol formation reached a maximum in the mid-solvent phase, when the butanol concentration was 50 mM. Although more solvent accumulated later, de novo enzyme synthesis decreased and then ceased.
我们研究了与丁酸梭菌产丁醇酶诱导相关的细胞内生理条件。在生长的产酸阶段，内部 pH 值随外部 pH 值的降低而降低，但整个分批培养过程中内部 pH 值并未低于 5.5。发现丁醇通过降低跨膜 pH 梯度来耗散发酵丁酸梭菌细胞的质子动力势，而膜电位仅受到轻微影响。在生长细胞中，当内部未离解丁酸浓度达到 13 mM 且总细胞内未离解酸浓度（乙酸加丁酸）至少为 40 至 45 mM 时，从酸到溶剂的转变发生。当最初用 50 mM 丁酸补充培养物或使用磷酸盐缓冲培养基代替乙酸盐缓冲培养基时，也获得了类似的值。为了测量参与溶剂合成的酶的诱导，我们测定了在生长细胞中丁酸转化为丁醇的速率。在溶剂中期，当丁醇浓度达到 50 mM 时，丁醇的形成速率达到最大值。尽管后来积累了更多的溶剂，但新酶的合成减少，然后停止。
