Compatible Solutes in the Akinetes of the Terrestrial Cyanobacterium Nostoc sp. HK-01 Contribute to Its Heat Tolerance

摘要

The detailed mechanisms that facilitate the heat tolerance of terrestrial cyanobacteria have not been completely elucidated, although several reports have revealed aspects of the heat tolerance mechanisms of several other organisms. The dormant cells, called akinetes, of the terrestrial cyanobacterium style="font-family:Verdana;">Nostoc style="font-family:Verdana;"> sp. HK-01 can revive after dry heat exposure at 100 style="white-space:nowrap;">℃ for more than 10 h. We investigated the compatible solutes that protect the biomolecules in style="font-family:Verdana;">Nostoc style="font-family:Verdana;"> sp. HK-01 akinetes using colonies containing various proportions of akinetes. We extracted the intracellular substances from each colony with 80% ethanol, which we purified with a series of analytical columns and analyzed by high- style="font-family:Verdana;">performance liquid chromatography and liquid chromatography style="font-family:Verdana;">- style="font-family:Verdana;">electrospray ionization style="font-family:Verdana;">- style="font-family:;" "=""> style="font-family:Verdana;">mass spectrometry. The compatible solutes were screened for their ability to prevent protein aggregation upon heating using the model enzyme lactate dehydrogenase. We detected an accumulation of glucosylglycerol, betaine, and glycine in akinetes. In addition, we confirmed that betaine, glycine, sucrose, and trehalose contributed to the prevention of the protein aggregation. The levels of sucrose and glycine in the colonies were approximately 1000× higher than those of glucosylglycerol, betaine, or trehalose. Our results indicated that sucrose and glycine are the main compatible solutes in the hydrophilic fractions of the cell extracts of style="font-family:Verdana;">Nostoc style="font-family:Verdana;"> sp. HK-01 akinetes.