Membrane phase behavior of a psychrotrophic and mesophilic bacillus

The phase properties of membranes isolated from the psychrotrophBacillus psychrophilus and the mesophileB. megaterium were examined using wide-angle X-ray diffraction. The temperature at which the transition from liquid-crystalline to crystalline (gel) phase occurred was below −30°C for both microorganisms, regardless of the temperature at which the microbial cells were grown. Thus the membranes for both microorganisms were exclusively liquid-crystalline over the entire growth temperature range. Indeed, the membrane was completely fluid at temperatures where growth of the psychrotroph ceases, thus indicating that the phase transition temperature is not the determinant of the minimum growth temperature.