Cold Tolerance in Cyanobacteria and Life in the Cryosphere

Cyanobacteria are commonly thought of as microbial phototrophs that are characteristic of warm water environments such as hot springs (Steunou et al., 2006), stratified lakes during summer (Vazquez et al., 2005) and tropical oceans (Johnson et al., 2006). It is less widely known that many cyanobacterial taxa achieve their greatest ecological success at the opposite thermal extreme, in polar and alpine environments. One of the first discoveries of the prolific growth of cyanobacteria in the cryosphere (the ensemble of cold environments containing snow and ice) was by the Swedish-Finnish explorer Adolf Erik Nordenskiöld. In his expedition across the Greenland Ice Cap in 1870 his team discovered black sediment that he called ‘cryoconite’, cold rock dust collecting in melt holes (Leslie, 1879). On closer inspection they observed that this material was composed of not only inorganic sediments but also black-pigmented cyanobacteria, now known to be mostly the heterocystous species Calothrix parietina (Gerdel and Drouet, 1960). They concluded that because of its dark colouration, this cyanobacteria and its bound sediment absorbs radiation and hastens melting of the ice, a process more recently documented on glaciers (Takeuchi et al., 2001) and ice shelves in the Canadian High Arctic (Mueller and Vincent, 2006).