COLD TEMPERATURE ADAPTATION AND GROWTH OF MICROORGANISMS

Most microorganisms must accommodate a variety of changing conditions and stresses in their environment in order to survive and multiply. Be cause of the impact of temperature on all reactions of the cell, adapt ations to fluctuations in temperature are possibly the most common. Wi despread in the environment and well-equipped for cold temperature gro wth, psychrophilic and psychrotrophic microorganisms may yet make nume rous adjustments when faced with temperatures lower than optimum. Phos pholipid and fatty acid alterations resulting in increased membrane fl uidity at lower temperatures have been described for many cold toleran t microorganisms while others may make no similar adjustment. While th e enzymes of cold growing bacteria have been less extensively studied than those of thermophilic bacteria, it appears that function at low t emperature requires enzymes with flexible conformational structure, in order to compensate for lower reaction rates. In many organisms, incl uding psychrophilic and psychrotrophic bacteria, specific sets of cold shock proteins are induced upon abrupt shifts to colder temperatures. While this cold shock response has not been fully delineated, it appe ars to be adaptive, and may function to promote the expression of gene s involved in translation when cells are displaced to lower temperatur es. The cold shock response of Escherichia coli has been extensively s tudied, and the major cold shock protein CspA appears to be involved i n the regulation of the response. Upon cold shock, the induction of Cs pA and its counterparts in most microorganisms studied is prominent, b ut transient; studies of this response in some psychrotrophic bacteria have reported constitutive synthesis and continued synthesis during c old temperature growth of CspA homologues, and it will be interesting to learn if these are common mechanisms of among cold tolerant organis ms. Psychrotrophic microorganisms continue to be a spoilage and safety problem in refrigerated foods, and a greater understanding of the phy siological mechanisms and implications of cold temperature adaptation and growth should enhance our ability to design more effective methods of preservation.