spoT-dependent accumulation of guanosine tetraphosphate in response to fatty acid starvation in Escherichia coli.

We previously isolated a mutant of Escherichia coli that is preferentially affected in the synthesis of rRNA and has a mutation in the gene (accD) encoding a subunit of acetyl-CoA carboxylase. Using this mutant and other mutants of the pathway for fatty acid and phospholipid biosynthesis as well as cerulenin, a specific inhibitor of fatty acid synthesis, we show that (i) inhibition of fatty acid synthesis in the presence of both a carbon source and all 20 amino acids stimulates the accumulation of guanosine tetraphosphate (ppGpp) and leads to preferential inhibition of rRNA synthesis, (ii) this ppGpp accumulation is spoT dependent, and (iii) the generation of the metabolic signal that stimulates this spoT-mediated response probably does not depend on either phospholipid starvation or a significant reduction in the level of ATP.