Abstract
The heat tolerance of dry colonies of a terrestrial cyanobacterium, Nostoc sp. HK-01 by exposure to temperatures at 100 °C, the boiling point of liquid water, was examined. The cells of Nostoc sp. HK-01 can live under these conditions for 10 hours. All of the viable cells were akinetes which are dormant cells. Akinetes have a high tolerance to high temperatures. The photosynthetic ability of cells of HK-01 was normal even after the heat exposure. The percentage of decreased water content in the dry colony was 5 percent during the heat exposure for 24 hours. The reasons for the decrease in the percentage of survival rates of colonies under the high heat condition are related to the remaining water in the dry colony, and/or, DNA damage of individual cells. Furthermore, there is a possibility that there are highly tolerant cells in the dry colony since there are cells that survived over 24 hours after the heat exposure.
