Jin S, Levin P A, Matsuno K, Grossman A D, Sonenshein A L
Department of Molecular Biology and Microbiology, Tufts University School of Medicine, Boston, Massachusetts 02111, USA.
J Bacteriol. 1997 Aug;179(15):4725-32. doi: 10.1128/jb.179.15.4725-4732.1997.
A Bacillus subtilis mutant with a deletion of citC, the gene encoding isocitrate dehydrogenase, the third enzyme of the tricarboxylic acid branch of the Krebs cycle, had a greatly reduced ability to sporulate. Analysis of expression of lacZ fusions to various sporulation gene promoters revealed that in the citC mutant development is probably blocked between stage 0 and stage II. That is, genes expressed very early in sporulation, under the direct control of the Spo0A transcription factor, were induced normally in the citC mutant. However, genes expressed after asymmetric septation (stage II) in wild-type cells were not induced in the citC mutant. Analysis of cell morphology by thin-section electron microscopy and immunofluorescence microscopy showed that the mutant formed axial chromosomal filaments and accumulated rings of FtsZ protein at potential polar division sites but failed to form asymmetric division septa, indicating that sporulation is blocked at stage I. The growth and sporulation defects of the B. subtilis citC mutant were fully overcome by introduction and expression of the Escherichia coli icd gene, encoding an isocitrate dehydrogenase similar to the enzyme from B. subtilis.
枯草芽孢杆菌的一个突变体缺失了citC基因，该基因编码异柠檬酸脱氢酶，即三羧酸循环（克雷布斯循环）分支中的第三种酶，其芽孢形成能力大幅降低。对与各种芽孢形成基因启动子融合的lacZ表达进行分析表明，在citC突变体中，发育可能在0期和II期之间受阻。也就是说，在芽孢形成早期、受Spo0A转录因子直接控制下表达的基因，在citC突变体中能正常诱导表达。然而，在野生型细胞中不对称隔膜形成后（II期）表达的基因，在citC突变体中并未被诱导表达。通过超薄切片电子显微镜和免疫荧光显微镜对细胞形态进行分析表明，该突变体形成了轴向染色体丝，并在潜在的极性分裂位点积累了FtsZ蛋白环，但未能形成不对称分裂隔膜，这表明芽孢形成在I期受阻。通过导入并表达大肠杆菌的icd基因（编码一种与枯草芽孢杆菌的酶类似的异柠檬酸脱氢酶），完全克服了枯草芽孢杆菌citC突变体的生长和芽孢形成缺陷。
