EFFECT OF INCUBATION MEDIA ON RECOVERY OF ESCHERICHIA-COLI-K12 HEATED AT 52-DEGREES-C

The exposure of exponentially grown E. coli K12 to 52.degree. C for 30 min in Tris/Mg2+ buffer resulted in a considerable loss of viability when plated on tryptone agar. When such heated bacteria were held at 37.degree. C for 2 h in tryptone broth before plating on tryptone agar, there was a significant increase in viability. Thus, heat damage was repaired in tryptone broth but not on tryptone agar. Recovery was greater in tryptone broth than in synthetic medium. In tryptone broth, recA or polA mutants also recovered but a lex mutant did not. As a result of heating, the sensitivity of bacteria to UV radiation, to mitomycin C and to plating on high salt medium was enhanced. After incubation for 2 h in tryptone broth at 37.degree. C, the bacteria regained their resistance to UV and mitomycin C and tolerance to high salt medium. Recovery of viability required RNA and protein synthesis, but recovery of UV resistance did not require protein synthesis. Heating for 30 min inhibited the release of acid-soluble material from DNA in all strains of E. coli used.