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Methionineless death in Escherichia coli
Abstract:
Methionine auxotrophs of strains derived from Escherichia coli 15 lose their colony-forming ability when deprived of this amino acid. Late addition of methionine to liquid cultures did not restore plating efficiency but permitted growth of surviving cells. This phenomenon, termed methionineless death (mld), was not observed with methionine auxotrophs of E. coli strains B, W, or K(12), nor was a similar amino acidless death observed with corresponding auxotrophs of E. coli 15 for arginine, tryptophan, proline, isoleucine, and leucine. Mld was not dependent upon the genetic site determining methionine auxotrophy, nor did it affect the decarboxylation of methionine or the stability of methionyl-transfer ribonucleic acid synthetase activity of starved cells. Death was not altered by the presence of spermine or spermidine but was abolished by the methionine analogue, alpha-methylmethionine. Simultaneous starvation of another amino acid in a multiple auxotroph also significantly reduced mld, suggesting a possible role of protein synthesis. The onset of mld is correlated with a lower net increase of deoxyribonucleic acid.
Insights
Methionineless death (mld) in Escherichia coli 15 occurs when methionine is absent, causing cell death. This specific phenomenon was not observed in other E. coli strains or with different amino acid deprivations.
Area of Science:
- Microbiology
- Molecular Biology
- Bacterial Physiology
Background:
- Certain strains of Escherichia coli exhibit a phenomenon known as methionineless death (mld) when deprived of methionine.
- This specific cell death is unique to methionine auxotrophs of E. coli 15 and not observed in other strains or with other amino acid deprivations.
Purpose of the Study:
- To investigate the characteristics and underlying mechanisms of methionineless death (mld) in Escherichia coli 15.
- To determine if mld is specific to methionine or if similar phenomena occur with other essential amino acids.
Main Methods:
- Comparative analysis of methionine auxotrophs from different E. coli strains (15, B, W, K(12)) under amino acid starvation.
- Assessment of cell viability, growth recovery, and biochemical parameters (methionine decarboxylation, methionyl-tRNA synthetase activity) during starvation.
- Evaluation of the effect of methionine analogues and simultaneous starvation of other amino acids on mld.
Main Results:
- Methionineless death (mld) was observed exclusively in E. coli 15 methionine auxotrophs, not in other strains or with other amino acid deprivations.
- Late methionine addition did not restore viability, but allowed growth of survivors. Mld was not linked to genetic site, methionine decarboxylation, or methionyl-tRNA synthetase stability.
- Mld was abolished by alpha-methylmethionine and reduced by simultaneous starvation of other amino acids, suggesting a role for protein synthesis and a correlation with reduced DNA synthesis.
Conclusions:
- Methionineless death (mld) is a specific phenomenon in E. coli 15, distinct from general amino acid starvation responses.
- The onset of mld is associated with reduced deoxyribonucleic acid synthesis and potentially influenced by protein synthesis levels.
- Further research is warranted to elucidate the precise molecular pathways leading to mld in E. coli.