ABSTRACT
Akinetes of cyanobacteria have been shown to be tolerant to desiccation (Yamamoto, 1975; Sutherland et al., 1979; Rai and Pandey, 1981; Sili et al., 1994; Baker and Bellifemine, 2000) and seven year-old desiccated akinetes exhibited germination (Sili et al., 1994). Sediments as old as 64 years revealed the presence of viable akinetes (Livingstone and Jaworskii, 1980). The thermal tolerance of akinetes, represented by their germination capacity after heat treatments, varied from species to species. The germination potential of Anabaena vaginicola akinetes was almost completely lost after heat treatment at 55°C for 8 min or 60°C for 2 min (Rai and Pandey, 1981) while the akinetes of Anabaena circinalis survived a heat treatment of 45°C for 60 min (Baker and Bellifemine, 2000). Akinetes of Anabaena dried in sunlight (10 h) and by heat treatment (60°C for 50 h) germinated only up to 40% and 15%, respectively (Hori et al., 2003). Akinetes of A. circinalis have been reported to be susceptible to ultraviolet radiations (Fay, 1988). Dried akinetes of Anabaena cylindrica exposed to desiccation (28 d) and extreme low temperature (–80ºC) survived better than those subjected to vacuum (0.7 x 10-3 KPa) and high temperature (80ºC) under the laboratory conditions. Some proportion of the akinetes also survived for a period of 10 d in low Earth Orbit and also simulated conditions of Mars without UV radiations (28 d) (Olsson-Francis et al., 2009).
