Survival of Escherichia coli during long-term starvation: effects of aeration, NaCl, and the rpoS and osmC gene products

The survival of Escherichia coli was investigated during long-term starvati on in rich media. In aerated cultures, E. coli lost the ability to form col onies earlier in NaCl-free Luria broth than in LB medium containing NaCl. I mproved survival at low aeration and the sensitivity to hydrogen peroxide i n aging cultures indicated a major role for oxidative stress in cell mortal ity. Mutants in rpoS, lacking the sigma (s) subunit of RNA polymerase, show ed altered survival in salt-containing media. However, in the absence of Na Cl, although these mutants exhibited a massive loss of viability during the first 2 days, this was followed by a stabilization of the number of surviv ors. The starved culture contained survivors until at least day 9, long aft er a wild-type strain had completely lost viability. This peculiar behavior suggests that, in rich media of low osmotic pressure, sigma (s) helps in s hort-term survival but hampers long-term survival. Mutants in osmC, a membe r of the rpoS regulon, also exhibited reduced survival and increased sensit ivity to oxidative stress. The biochemical function of the envelope protein OsmC remains unknown, but present data indicated that it participates, dir ectly or indirectly, in the defense against oxidative compounds. (C) 2001 E ditions scientifiques et medicales Elsevier SAS.