Exponentially growing tetracycline-treated Escherichia coli cells rele
ase (an) as yet unidentified compound(s) into the medium. These compou
nds produce a protective effect on E. coli cells under conditions of h
eat, oxidative, and osmotic shocks, or in the presence of tetracycline
. The protective effect is manifested as an acceleration of growth in
the presence of tetracycline or under conditions of heat shock or as a
shortening of the period of adaptation to other stresses.