TITLE:
Compatible Solutes in the Akinetes of the Terrestrial Cyanobacterium Nostoc sp. HK-01 Contribute to Its Heat Tolerance
AUTHORS:
Shunta Kimura, Midori Ong, Sosaku Ichikawa, Kaori Tomita-Yokotani
KEYWORDS:
Akinete, Compatible Solute, Cyanobacteria, Dry Heat Tolerance, Nostoc sp. HK-01
JOURNAL NAME:
American Journal of Plant Sciences,
Vol.8 No.11,
October
19,
2017
ABSTRACT: 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 Nostoc sp. HK-01 can
revive after dry heat exposure at 100℃ for more than 10 h. We investigated the
compatible solutes that protect the biomolecules in Nostoc 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-performance
liquid chromatography and liquid chromatography-electrospray ionization-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 Nostoc sp. HK-01 akinetes.