Determining the limits of microbial life at subzero temperatures

Determining the low-temperature limit of life is a challenge complicated by the reduced availability of liquid water as water freezes and by the low rates of diffusion and reaction brought on by low temperatures. And yet, many microorganisms are able to grow at temperatures of -2 °C to 4 °C and many also survive much lower temperatures of -80 °C to -196 °C. A variety of approaches for determining the low-temperature limit of life are examined in this chapter and relevant data are reported. Theoretical approaches investigate the presence of liquid water at temperatures below 0 °C as well as universal laws of biology which may inform the low-temperature limits of life. Both reductionist and holistic experimental approaches reveal the known limits of cellular components, processes, and whole cells with multiple lines of evidence suggesting that cell reproduction occurs down to temperatures of -20 °C. Finally, observational studies of microorganisms in low-temperature environments of the polar regions expose how the low-temperature limit of life is entangled with other factors (perhaps inextricably) and that time at low temperatures may limit evolution and cold adaptation of terrestrial life.