Lipid synthesis in stringent Escherichia coli: an artifact in acetate labeling of phospholipids during a shiftdown in growth rate

Evidence that glucose starvation-sensitive mutants are altered in the relB locus

Genetic mapping studies indicate that the relaxed-control mutants isolated on the basis of sensitivity to glucose starvation contain lesions in the relB locus. These mutants, which are sensitive to protein synthesis inhibitors such as sulfacetamide, exhibit relaxed control of both RNA and phospholipid syntheses.

Regulation of fatty acid synthesis during the cessation of phospholipid biosynthesis in Escherichia coli

In 1975, Cronan et al. (J. Biol. Chem. 250:5835-5840) reported that free fatty acids accumulated during glycerol starvation of an Escherichia coli glycerol auxotroph. On the basis of labeling experiments showing significant incorporation of [14C]acetate into the fatty acid fraction of glycerol-starved cells, these authors concluded that fatty acid synthesis proceeded normally in the absence of phospholipid synthesis. Since these findings might have been due to an increase in the intracellular specific activity of the [1-14C]acetyl coenzyme A pool of the glycerol-starved cells, we reexamined the effect of glycerol starvation on fatty acid synthesis. We found that (i) the incorporation of 3H2O and/or [2,3-14C]succinate into the fatty acid fraction of glycerol auxotrophs is severely reduced during starvation, (ii) the incorporation of [1-14C]acetate into the lipid fraction of an acetate-requiring glycerol auxotroph is inhibited by 95% during glycerol starvation, and (iii) the accumulation of fatty acids, as measured by microtitration, in glycerol-starved cells is less than 10% that of glycerol-supplemented cells. These results indicate that fatty acid synthesis is inhibited in the absence of phospholipid synthesis of E. coli.

Stringent control of peptidoglycan biosynthesis in Escherichia coli K-12

[3H]Diaminopimelic acid (Dap) was incorporated exclusively into peptidoglycan by Escherichia coli strains auxotrophic for both lysine and Dap. The rate of [3H]Dap incorporation by stringent (rel+) strains was significantly decreased when cells were deprived of required amino acids. The addition of chloramphenicol to amino acid-starved rel+ cultured stimulated both peptidoglycan and ribonucleic acid synthesis. In contrast, a relaxed (relA) derivative incorporated [3H]Dap at comparable rates in the presence or absence of required amino acids. Physiologically significant concentrations of guanosine 5'-diphosphate 3'-diphosphate (ppGpp) inhibited the in vitro synthesis of both carrier lipid-linked intermediate and peptidoglycan catalyzed by a particulate enzyme system. The degree of inhibition was dependent on the concentration of ppGpp in the reaction mixture. Thus, the results of in vivo and in vitro studies indicate that peptidoglycan synthesis is stringently controlled in E. coli.