Serine Starvation Research Articles

Genetic transformation in a synchronous culture of Streptococcus pneumoniae.

Cultures of synchronized Streptococcus pneumoniae cells were prepared by amino acid starvation followed by refeeding, and the cellular reactivity towards the competence-activator for genetic transformation, i.e., competence induction on the addition of the activator, was investigated. Cyclical fluctuation in the level of competence was observed during the cell cycle. Especially, cells at division showed reduced cellular ability to develop competence. It was also observed that deprivation of nutritionally required amino acids had quite different effects on the induction of competence, depending upon the amino acid removed: glutamine or serine starvation caused a significant reduction in the level of competence induced by the activator, whereas deprivation of other amino acids (histidine, leucine, isoleucine, valine, arginine and cysteine) did not.

Accumulation of ppGpp in a relA mutant of Escherichia coli during amino acid starvation.

In Escherichia coli, amino acid starvation triggers the rapid synthesis of two guanosine polyphosphates, pppGpp and ppGpp (the 3'-pyrophosphates of GTP and GDP, respectively). Determination of the turnover rate of the ppGpp pool indicated that during serine deprivation, as opposed to other amino acid starvations, the rate of ppGpp degradation is dramatically decreased. This results in a slow but significant accumulation of this regulatory nucleotide in a relA mutant during serine starvation. Similar ppGpp accumulation can be seen during serine starvation in different serine auxotrophic mutants carrying different relA alleles. On the other hand, no ppGpp accumulation is induced in various relaxed strains by serine hydroxamate treatment.

Effect of Serine Hydroxamate on Phospholipid Synthesis in Escherichia coli

Serine hydroxamate, which inhibits the charging of seryl-transfer ribonucleic acid, reduced the synthesis of phospholipid and nucleic acids in Escherichia coli. This effect was analogous to depriving amino acid auxotrophs of their nutritional requirement and appears to be a manifestation of the stringent response shown by rel(+) strains of E. coli. Amino acid starvation (serine or methionine) alone or serine hydroxamate treatment alone results in 60 to 80% inhibition of lipid accumulation, 90% inhibition of ribonucleic acid accumulation, and an increase in guanosine tetraphosphate (ppGpp). These three effects were reversed by addition of chloramphenicol (CM). A combination of serine starvation and serine hydroxamate treatment resulted in inhibition of lipid and RNA accumulation as well as an increase in ppGpp, but the consequences of the double block were not reversed by CM. We conclude that a strong interrelationship exists among these processes and that CM acts to relax a stringent response by mechanisms other than interference with ppGpp formation. All species of phospholipid were affected by a stringent response evoked by amino acid starvation or addition of serine hydroxamate, but in all cases the synthesis of phosphatidylethanolamine was most severely inhibited. Serine hydroxamate was not incorporated into lipid but specifically caused phosphatidylserine accumulation. Serine starvation produced a dramatic alteration of the distribution of isotope incorporated into phospholipid, which resulted from the stringent response compounded with the limitation of a substrate for phosphatidylserine synthesis.