Role of protein synthesis in the survival of carbon-starved Escherichia coli K-12

Abstract

In a typical Escherichia coli K-12 culture starved for glucose, 50% of the cells lose viability in ca. 6 days (Reeve et al., J. Bacteriol. 157:758-763, 1984). Inhibition of protein synthesis by chloramphenicol resulted in a more rapid loss of viability in glucose-starved E. coli K-12 cultures. The more chloramphenicol added (i.e., the more protein synthesis was inhibited) and the earlier during starvation it was added, the greater was its effect on culture viability. Chloramphenicol was found to have the same effect on a reLA strain as on an isogenic reU+ strain of E. coli. Addition of the amino acid analogs S-2-aminoethylcysteine, 7-azatryptophan, and p-fluorophenylalanine to carbon-starved cultures to induce synthesis of abnormal proteins had an effect on viability similar to that observed when 50 ,ug of chloramphenicol per ml was added at zero time for starvation. Both chloramphenicol and the amino acid analogs had delayed effects on viability, compared with their effects on synthesis of normal proteins. The need for protein synthesis did not arise from cryptic growth, since no cryptic growth of the starving cells was observed under the conditions used. From these and previous results obtained from work with peptidase-deficient mutants of E. coli K-12 and Salmonella typhimurium LT2 (Reeve et al., J. Bacteriol. 157:758-763, 1984), we concluded that a number of survival-related proteins are synthesized by E. coli K-12 cells as a response to carbon starvation. These proteins are largely synthesized during the early hours of starvation, but their continued activity is required for long-term survival.Starving bacteria are of interest in both an ecological and an applied context, and we have been interested in characterizing the physiological changes that occur during starvation (12,16,22). We have previously presented evidence (16) that protein degradation plays a role in the survival of carbon-starved bacteria. Mutants of Escherichia coli and Salmonella typhimurium that were deficient in protein degradation were found to possess a greatly decreased stability under conditions of carbon starvation. Although these mutants had no innate deficiency in their protein-synthetic machinery, they were unable to synthesize protein at the same rate as their corresponding wild-type strains during carbon starvation. This suggested that amino acids derived from protein degradation were utilized by these cells for new protein synthesis and that their increased susceptibility to carbon starvation originated from their inability to synthesize these proteins.In E. coli cells subjected to carbon starvation, the rate of protein synthesis drops to about 20% of the initial rate during the first hour of starvation (16) and then remains roughly constant for at least the next 47 h (unpublished data). We present evidence here that this protein synthesis is important for the survival of carbon-starved E. coli K-12; inhibition of normal protein synthesis during starvation greatly compromised survival. MATERIALS AND METHODSBacterial strains, ...

Escherichia coliis naturally transformable in a novel transformation system

“…The inability of plasmid pUC-cm to transfer a Cm r gene is not due to an inherent inability of E. coli to maintain the plasmid, as it can be artificially transformed into E. coli or naturally transformed into E. coli containing an Amp r marker and subsequently maintained. We suggest that chloramphenicol interrupted transformation by preventing the plasmid entering cells through inhibition of the synthesis of proteins required for DNA uptake (Reeve et al, 1984). When the chloramphenicol-containing upper layer was plated after 9 h of incubation, there were no effects on transformation efficiency, thus demonstrating that the transformation process was completed within 9 h.…”

Bacteria starved for prolonged periods develop increased protection against lethal temperatures

“…It has been demonstrated for both ,2-. coli and I4brio cells that an on-going protein synthesis and the expression of starvation specific proteins are necessary for prolonged survival during multiple as well as carbon starvation [5,22]. The molecular and physiological adaptation of I, qbrio cells during starvation has recently been reviewed.…”

Dormancy in non-sporulating bacteria

“…We wish to stress that these genetic studies deal with starvation processes but not with the transition to dormancy per se (which is evidently one of the possible consequences of starvation). Moreover, in these studies, the decrease of cell viability is judged on the basis of colony counts on agar plates, and changes in viability as an indicator of cell death and thus sensitivity to starvation [23,45]. However, it can not be excluded (and is in our view, on the basis of the material reviewed here, rather likely) that such a decrease actually reflects the formation of dormant cells.…”

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