Craig J E, Ford M J, Blaydon D C, Sonenshein A L
Department of Molecular Biology and Microbiology, Tufts University School of Medicine, Boston, Massachusetts 02111, USA.
J Bacteriol. 1997 Dec;179(23):7351-9. doi: 10.1128/jb.179.23.7351-7359.1997.
The citB gene of Bacillus subtilis encodes aconitase, the enzyme of the Krebs citric acid cycle, which is responsible for the interconversion of citrate and isocitrate. A B. subtilis strain with an insertion mutation in the citB gene was devoid of aconitase activity and aconitase protein, required glutamate for growth in minimal medium, and was unable to sporulate efficiently in nutrient broth sporulation medium. Mutant cells failed to form the asymmetric septum characteristic of sporulating cells and were defective in transcription of the earliest-expressed spo genes, that is, the genes dependent on the Spo0A phosphorelay. However, this early block in sporulation was partially overcome when cells of the citB mutant were induced to sporulate by resuspension in a poor medium. Accumulation of citrate in the mutant cells or in their culture fluid may be responsible for the early block, possibly because citrate can chelate divalent cations needed for the activity of the phosphorelay.
枯草芽孢杆菌的citB基因编码乌头酸酶，这是三羧酸循环中的一种酶，负责柠檬酸和异柠檬酸的相互转化。在citB基因中存在插入突变的枯草芽孢杆菌菌株缺乏乌头酸酶活性和乌头酸酶蛋白，在基本培养基中生长需要谷氨酸，并且在营养肉汤芽孢形成培养基中不能有效地形成芽孢。突变细胞未能形成芽孢形成细胞特有的不对称隔膜，并且在最早表达的spo基因（即依赖Spo0A磷酸化传递的基因）的转录方面存在缺陷。然而，当citB突变体的细胞通过重悬于不良培养基中被诱导形成芽孢时，这种芽孢形成的早期阻断被部分克服。突变细胞或其培养液中柠檬酸的积累可能是造成早期阻断的原因，可能是因为柠檬酸可以螯合磷酸化传递活性所需的二价阳离子。
