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Escherichia coli W3110 was grown in a chemostat under conditions of carbon limitation at various temperatures and specific growth rates (μ). Exponential survivor-time curves following cold osmotic shock were biphasic. These could be described by the sum of two exponential functions representing the survival of sensitive and resistant fractions of the population where the size of the sensitive fraction was directly proportional to μ. Decimal reduction times for the more resistant fraction were unaffected by μ yet decreased with increasing growth temperature.
Sensitivity to cold shock was evaluated for an E. coli CR34 mutant, temperature-sensitive in initiation of DNA replication. When grown in the chemostat at the nonrestrictive temperature (30°C) sensitivity was directly proportional to μ . Following a rise in the incubation temperature to 42°C, sensitivity decreased markedly and reached a minimum 45 to 60 min after the temperature increase. Sensitivity of the E. coli mutant grown at 30°C and raised to 42°C for 1 h was low and relatively unaffected by growth rate.
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