Complete Life Cycle and Heat Tolerance of Dry Colonies of a Terrestrial Cyanobacterium, <i>Nostoc</i> sp. HK-01

Abstract

The exact life cycle of cells in a terrestrial cyanobacterium, Nostoc sp. HK-01 which has several different types of cells, was confirmed by microscopic observation. All of types of cells were individually observed during 30-days of liquid incubation. The germination process from akinetes was recognized twice during the incubation period. The contribution of extracellular polysaccharides, EPS, for tolerance to heat in the dried colonies of Nostoc sp. HK-01 was also investigated. The survival rate of dried colonies of Nostoc sp. HK-01 with and without EPS were examined after exposure to temperatures at 100˚C. The contribution to heat tolerance of EPS was tested and verified by the cell staining method. The survival rate of both groups of cells, with EPS and without EPS, of Nostoc sp. HK-01 was not remarkably different and they both lived under these conditions for 12 hours. These results indicate that the contribution of EPS to their heat tolerance would be very low. The amounts of sucrose and trehalose in the dry colonies were investigated to determine the contribution to heat tolerance in akinete as a compatible solute. The amount of trehalose was lower than that of sucrose in the dry colonies. It can be assumed that trehalose did not contribute to their heat tolerance.©2017 Jpn. Soc. Biol. Sci.

Compatible Solutes in the Akinetes of the Terrestrial Cyanobacterium &lt;i&gt;Nostoc&lt;/i&gt; sp. HK-01 Contribute to Its Heat Tolerance

“…The accumulation of sucrose specifically in the akinetes of Nostoc sp. HK-01 has already been reported by Kimura et al [33]. The presence of trehalose in the colonies has also already been reported, although not specifically in the akinetes [33].…”

“…HK-01 akinetes could contribute to its heat tolerance as compatible solutes, including sucrose [33]. We isolated and identified substances other than sucrose (Figure 3).…”

“…We also detected trehalose in colonies of Nostoc sp. HK-01, although not specifically in akinetes [33]. It is possible that sucrose and/or trehalose function in akinetes as compatible solutes, but there is no evidence that these compounds contribute to the dry heat tolerance of akinetes.…”

“…We previously reported that dried colonies of the terrestrial cyanobacterium Nostoc sp. HK-01 were able to revive after exposure to dry heat at 100˚C for more than 10 h [32] [33]. However, the detailed mechanisms of heat tolerance among terrestrial cyanobacteria have not been completely elucidated; several reports have partially revealed the mechanisms of heat tolerance in other organisms.…”

“…HK-01, we previously confirmed the accumulation of sucrose in akinetes by quantitative analysis. We used different ratios of akinetes in the colonies in order to verify that selected substances specifically accumulated in akinetes [33]. We also detected trehalose in colonies of Nostoc sp.…”