Survival of Common Bacteria in Liquid Culture under Carbon Dioxide at High Temperatures

Abstract

WE report results which are at variance with the general belief that high temperatures are necessarily lethal to microorganisms¹. Escherichia coil B, Aerobacter aerogenes, Bacillus subtilis, and Serratia marcescens were found to survive for 24 h in a CO₂ atmosphere at a temperature of up to 160° C. These organisms were routinely cultured in sterile trypticase soy broth (TSB) medium, and plated on TSB plates containing 1.5% of agar. Cultures were incubated at 37° C on a rotary shaker, sub-cultured every 48 h, and exposed to high temperatures and pressures while in the stationary phase, 48 h after subculturing. One millilitre of each culture was injected into 5 ml. glass tubes, which were then inserted into 75 m stainless steel bombs fitted with a plug and a needle valve, and flushed free of air with commercial grade CO₂ for 30 s before sealing and raising the pressure to up to 20 atm, and enclosing the entire bomb in an oven at 105–160° C for up to 24 h. Pyrene (m.p. 150° C) was liquefied inside such a bomb within 1 h at an oven temperature reading of 150° C, demonstrating effective heat transfer. Control tubes of each culture were maintained at 20° C in air during the experiment, to provide data on viability loss through standing.