A comparison of thermal adaptation of membrane lipids in psychrophilic and thermophilic bacteria

Bacteria can be categorized according to their growth ~,empcrature ranges into psychrophiles (0-20C), mesophiles (10-50C) and thermophiles (40-110C) 1; psychrophiles may also be able to grow below zero and there are reports of growth at temperatures as low as -12C 2.Individual members of the groups generally have temperature spans of 20-40 centigrade degrees, the same as most life forms, but as a group the bacteria span a much greater thermal range than any other.Some psychrophiles with particularly low optimum growth temperatures and some thermophiles with high optimum growth temperatures have rather restricted growth temperature ranges of approximately 15 centigrade degrees.Although it is convenient and useful to classify bacteria into thermal groups, taken together they display a continuum of thermal tolerance.The overlapping growth temperature ranges of the three groups are indicative that there are no real boundaries and this is emphasized by the existence of psychrotrophs (or