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Repression of sporulation in Bacillus subtilis by L-malate
Abstract:
L-Malate repressed sporulation in the wild-type strain of Bacillus subtilis. When 75 mM L-malate was added to the growth medium at the time of inoculation, the appearance of heat-resistant spores was delayed 6 to 8 h. The synthesis of extracellular serine protease, alkaline phosphatase, glucose dehydrogenase, and dipicolinic acid was similarly delayed. Sporulation was not repressed when malate was added to the culture at t4 or later. A mutant was selected for ability to sporulate in the presence of malate. This strain could also sporulate in the presence of glucose. The malate-resistant mutant grew poorly with malate as sole carbon source, although it possessed an intact citric acid cycle, and it showed increased levels of malic enzyme. This indicates a defect in the metabolism of malate in the mutant. A mutant lacking malate dehydrogenase activity was also able to sporulate in the presence of malate. A model for the regulation of sporulation by malate is presented and discussed. Citric acid cycle intermediates other than malate did not affect sporulation. In contrast to previous results, sporulation of certain citric acid cycle mutants could be greatly increased or completely restored by the addition of intermediates after the enzymatic block. The results indicate that the failure of citric acid cycle mutants to sporulate can be adequately explained by lack of energy and lack of glutamate.
Insights
L-Malate addition to Bacillus subtilis cultures repressed spore formation, delaying key sporulation factors. A malate-resistant mutant revealed defects in malate metabolism, impacting sporulation regulation.
Area of Science:
- Microbiology
- Molecular Biology
- Biochemistry
Background:
- Sporulation in Bacillus subtilis is a complex developmental process.
- The citric acid cycle plays a crucial role in cellular energy metabolism.
- Regulation of sporulation by nutrient availability is a key area of study.
Purpose of the Study:
- To investigate the effect of L-malate on Bacillus subtilis sporulation.
- To identify genetic factors involved in malate-mediated repression of sporulation.
- To elucidate the role of malate metabolism in the regulation of bacterial development.
Main Methods:
- Addition of L-malate to wild-type Bacillus subtilis cultures at different growth stages.
- Selection and characterization of malate-resistant sporulation mutants.
- Enzyme activity assays (malic enzyme, malate dehydrogenase) and growth studies.
Main Results:
- L-Malate significantly repressed sporulation and delayed the synthesis of key sporulation-associated enzymes and dipicolinic acid in wild-type Bacillus subtilis.
- Sporulation repression by L-malate was dependent on the timing of addition, with no effect after t4.
- A malate-resistant mutant exhibited poor growth on malate, increased malic enzyme levels, and a defect in malate metabolism, suggesting impaired malate utilization.
- A malate dehydrogenase-deficient mutant could sporulate in the presence of malate.
- Addition of citric acid cycle intermediates could restore sporulation in certain mutants, suggesting energy and glutamate limitation as causes for failure to sporulate.
Conclusions:
- L-Malate acts as a repressor of Bacillus subtilis sporulation, likely through its metabolic pathways.
- Mutational analysis identified a role for malate metabolism in the regulation of sporulation.
- Energy and glutamate availability are critical factors for successful sporulation in citric acid cycle mutants.