Cold Shock in a Mesophilic and a Psychrophilic Pseudomonad

Abstract

A mesophilic strain of Pseudomonas aeruginosa grown at 30[degree] and suspended to a concentration of equiv. 0.02 mg dry wt/ml in 30 m[image]-NaCl showed rapid loss of viability when chilled rapidly from 30[degree] to 0[degree] or [long dash]2[degree]. The viability of a psychrophilic pseudomonad grown at 30[degree] did not decrease to the same extent when a dilute suspension (equiv. 0.02 mg dry wt/ml) was rapidly chilled from 30[degree] to 0[degree] or [long dash]2[degree]. Concentrated suspensions (equiv. 3.0 mg dry wt/ml) of both the mesophile and the psychrophile released about the same proportion of total endogenous UV-absorbing compounds when rapidly chilled from 30[degree] - 5[degree], 0[degree] or [long dash]2[degree]. Loss of viability following rapid chilling of a dilute suspension of the mesophile or the psychrophile was partly or completely prevented by 5 m[image]Mg2+ and by bacteria-free filtrates from chilled concentrated suspensions of either bacterium. The viability of the bacteria grown at 10[degree] did not decrease when dilute suspensions were rapidly chilled from 10[degree] to [long dash]2[degree]. Bacteria grown at 10[degree] contained a greater proportion of unsaturated fatty-acids than bacteria grown at 30[degree]. Fatty-acid analyses showed that susceptibility of the mesophile and psychrophile to cold shock could be correlated with the contents of unsaturated fatty-acids in their lipids.