Tolerance of the widespread cyanobacterium Nostoc commune to extreme temperature variations (-269 to 105°C), pH and salt stress

Nostoc commune is a widespread colonial cyanobacterium living on bare soils that alternate between frost and thaw, drought and inundation and very low and high temperatures. We collected N. commune from alternating wet and dry limestone pavements in Sweden and tested its photosynthesis and respiration at 20A degrees C after exposure to variations in temperature (-269 to 105A degrees C), pH (2-10) and NaCl (0.02-50 g NaCl kg(-1)). We found that dry field samples and rewetted specimens tolerated exposure beyond that experienced in natural environmental conditions: -269 to 70A degrees C, pH 3-10 and 0-20 g NaCl kg(-1), with only a modest reduction of respiration, photosynthesis and active carbon uptake at 20A degrees C. (CO2)-C-14 uptake from air declined markedly below zero and above 55A degrees C, but remained positive. Specimens maintained a high metabolism with daily exposure to 6 h of rehydration and 18 h of desiccation at -18 and 20A degrees C, but died at 40A degrees C. The field temperature never exceeded the critical 40A degrees C threshold during the wet periods, but it frequently exceeded this temperature during dry periods when N. commune is already dry and unaffected. We conclude that has N. commune an excellent tolerance to low temperatures, long-term desiccation and recurring cycles of desiccation and rewetting. These traits explain why it is the pioneer species in extremely harsh, nutrient-poor and alternating wet and dry environments.