Suspensions of Serratia marcescens (ATCC strain 14041) in water were aerosolized in a rotating drum in the presence of various concentrations of oxygen. The colony-forming ability of aerosolized organisms was rapidly destroyed by contact with 0.25% or more oxygen at 40% relative humidity (RH) and 25 C, but was almost unimpaired for at least 5 hr in nitrogen containing not more than 10 ppm of oxygen. Completely hydrated organisms were insensitive to oxygen at pressures up to 100 psi for 4 hr. No loss in viability occurred in aerosols of washed cells in air at 97% RH. It is proposed that dehydration of the aerosolized cell results in sensitization to lethal effects of oxygen, but is not the primary cause of death. Mn ++ , Co ++ , glycerol, and thiourea enhanced the biological stability of aerosols in air. Numerous similarities between the effects of oxygen in this system and in systems using freeze-dried or irradiated organisms or cell-free enzymes support the hypothesis that closely related mechanisms are involved.

HESS, GEORGE E. (U. S. Army Chemical Corps, Fort Detrick, Maryland) AND MILTON SHON. Selection of thermostable Serratia marcescens from logarithmic-phase cultures as a means for inducing synchronous growth. J. Bacteriol. 83:781-784. 1962.-A relatively thermostable, apparently nonmultiplying, population of Serratia marcescens was found in cultures in the exponential phase of growth. Thermal treatment of the whole culture resulted in the death of the multiplying cell fraction, although the nonmultiplying fraction remained viable. Subcultivation of the thermally treated suspensions yielded cultures in which most of the viable organisms multiplied synchronously for at least two generations. Synchronous growth of organisms can be induced through various techniques (Campbell, 1957) which utilize the response of the organism to variables such as illumination level (von Denffer, 1958), incubation temperature (Lark and

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