Algae at Extreme Low Temperatures

Abstract

In vitro cryopreservation is the storage of viable cells at ultra-low temperatures (196C), usually in liquid nitrogen or its vapor phase. Under these conditions it is assumed that metabolism is arrested and cells are stable for indefinite periods, so long as liquid nitrogen supply is maintained. The fact that cells tolerate cryogenic temperatures is remarkable as survival after cryopreservation is common to a wide range of biodiversity. The in vitro cryobank is one of the most, if not the most extreme low-temperature environment that an organism, or component part thereof, will ever encounter on earth. It is fascinating to speculate how, with the aid of cryoprotection (Fuller, 2004) so many diverse life-forms survive such extreme cold. Cryopreservation has important applications for astrobiology and in vivo studies of extremophiles; as water and temperature are physical determinants of life, indeed water is a prerequisite for life. This chapter considers cryoconservation in a wider context, appraising the comparative utilities of both natural and artificial cryobanks as repositories and research tools that may be used to help understand how life survives extreme cold. Algae are the subject of choice as they are one of the oldest and most diverse groups of organisms; their ancestral, fossil remains have been found in strata dating from 1.4 billion to 2.1 billion years (Cloud et al., 1969; Han and Runnegar, 1992). Algae are ubiquitous primary producers and formidable extremophiles, yet, compared with other biological resources, their preservation in cryobanks (Day et al., 2005) and their utilization as a valuable economic resource remains limited.