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Journal of Bacteriology, June 1999, p. 3382-3391, Vol. 181, No. 11
Department of Molecular Biology and
Microbiology, Tufts University School of Medicine, Boston,
Massachusetts 02111,1 and Department of
Microbiology, Ohio State University, Columbus, Ohio
432102
Received 25 January 1999/Accepted 30 March 1999
A Bacillus subtilis mutant with a deletion in the
citC gene, encoding isocitrate dehydrogenase, the third
enzyme of the tricarboxylic acid branch of the Krebs cycle, exhibited
reduced growth yield in broth medium and had greatly reduced ability to
sporulate compared to the wild type due to a block at stage I, i.e., a
failure to form the polar division septum. In early stationary phase,
mutant cells accumulated intracellular and extracellular concentrations of citrate and isocitrate that were at least 15-fold higher than in
wild-type cells. The growth and sporulation defects of the mutant could
be partially bypassed by deletion of the major citrate synthase gene
(citZ), by raising the pH of the medium, or by
supplementation of the medium with certain divalent cations, suggesting
that abnormal accumulation of citrate affects survival of
stationary-phase cells and sporulation by lowering extracellular pH and
chelating metal ions. While these genetic and environmental alterations
were not sufficient to allow the majority of the mutant cell population to pass the stage I block (lack of asymmetric septum formation), introduction of the sof-1 mutant form of the Spo0A
transcription factor, when coupled with a reduction in citrate
synthesis, restored sporulation gene expression and spore formation
nearly to wild-type levels. Thus, the primary factor inhibiting
sporulation in a citC mutant is abnormally high
accumulation of citrate, but relief of this metabolic defect is not by
itself sufficient to restore competence for sporulation.
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Metabolic Imbalance and Sporulation in an
Isocitrate Dehydrogenase Mutant of Bacillus
subtilis
*
Corresponding author. Mailing address: Department of
Molecular Biology and Microbiology, Tufts University School of
Medicine, 136 Harrison Ave., Boston, MA 02111-1800. Phone: (617)
636-6761. Fax: (617) 636-0337. E-mail:
asonensh{at}opal.tufts.edu.
Present address: Department of Biotechnology, School of
Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka, Japan.
Journal of Bacteriology, June 1999, p. 3382-3391, Vol. 181, No. 11
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
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