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A decrease in S-adenosylmethionine synthetase activity increases the probability of spontaneous sporulation
Abstract:
Starting with a relaxed (relA) strain, mutants with reduced activity of adenosine triphosphate:L-methionine S-adenosyl transferase (EC 2.5.1.6; SAM synthetase) were isolated in Bacillus subtilis. One such mutant (gene symbol metE1) had only 3% of the normal SAM synthetase activity but grew almost as well as the parent strain. Another mutant was isolated (gene symbol spdC1) as being able to sporulate continually at a high frequency; it had one-half the normal SAM synthetase activity at 33 degrees C. Both mutants continually and spontaneously entered spore development at a higher frequency than the parent strain in a medium containing excess glucose, ammonium ions, and phosphate. Sporulation was prevented by a high concentration of SAM (1 mM or more) or by the combination of adenosine and methionine (0.5 mM or more each), both of which are precursors of SAM. In contrast to this continual increase in the spore titer, addition of decoyinine, an inhibitor of GMP synthetase, rapidly initiated massive sporulation. Various amino acid analogs also induced sporulation in the relA strain, the methionine analogs ethionine and selenomethionine being most effective.
Insights
Mutants of Bacillus subtilis with reduced SAM synthetase activity exhibit altered sporulation. High levels of S-adenosylmethionine (SAM) or its precursors inhibit sporulation, while decoyinine and amino acid analogs induce it.
Area of Science:
- Microbiology
- Molecular Biology
- Biochemistry
Background:
- Bacillus subtilis sporulation is a complex developmental process.
- Regulation of sporulation is influenced by nutrient availability and intracellular signaling molecules.
- S-adenosylmethionine (SAM) is a crucial methyl donor involved in various cellular processes.
Purpose of the Study:
- To investigate the role of SAM synthetase activity in Bacillus subtilis growth and sporulation.
- To identify mutants with altered SAM synthetase levels and characterize their sporulation phenotypes.
- To explore the effects of SAM, its precursors, and other small molecules on sporulation frequency.
Main Methods:
- Isolation and characterization of Bacillus subtilis mutants with reduced SAM synthetase activity (metE1, spdC1).
- Growth analysis and sporulation assays under various conditions.
- Treatment with S-adenosylmethionine (SAM), adenosine, methionine, decoyinine, and amino acid analogs.
Main Results:
- Mutants with significantly reduced SAM synthetase activity showed near-normal growth but increased spontaneous sporulation.
- High concentrations of SAM or its precursors (adenosine and methionine) inhibited sporulation.
- Decoyinine (GMP synthetase inhibitor) and certain amino acid analogs (ethionine, selenomethionine) potently induced sporulation in the relA strain.
Conclusions:
- SAM synthetase activity is not essential for Bacillus subtilis growth but plays a regulatory role in sporulation.
- Intracellular SAM levels appear to negatively regulate sporulation initiation.
- Specific signaling molecules and amino acid analogs can override normal regulatory pathways to trigger sporulation.