General Characteristics of Cold-Adapted Microorganisms

Although interest in microbes inhabiting low-temperature environments has increased in recent years, significant gaps remain in understanding what makes certain microorganisms cold adapted. Interest in the structural, biochemical, and physiological properties of psychrophilic microorganisms has motivated investigations to characterize the adaptations that maintain enzymatic reaction rates, macromolecular stability, and homeostasis at cold temperature. This chapter provides an overview on the state of knowledge about adaptations that allow certain bacteria and archaea to persist in the coldest regions of the biosphere. In general, the proteins of psychrophilic microorganisms must maintain flexibility to perform catalysis at low temperatures, whereas thermophilic proteins are rigid to protect them from thermal denaturation. Importantly, adaptations that enhance protein flexibility reduce the activation energy needed for the formation of the enzyme-substrate complex, resulting in enhanced catalytic activity at low temperature. The chapter discusses many of the most common and generally understood biochemical and physiological adaptations that appear unique to the psychrophilic lifestyle. Psychrophilic microorganisms use a range of strategies to persist at low temperatures, including possessing catalytically efficient enzymes, synthesizing specialized lipids that increase membrane flexibility, and producing proteins that affect freezing and ice structure. Coupled with technological advances in high-throughput DNA sequencing and proteomics, one can expect that information on cold-adapted bacteria and archaea will increase in the future.