Japanese sake: the new pick-me-up? Yeast strain makes fatigue-fighting ornithine

Date:
August 27, 2020
Source:
Nara Institute of Science and Technology
Summary:
Researchers have found that that a mutant strain of sake yeast
produces high levels of the amino acid ornithine. Ornithine has
been found to reduce fatigue and improve sleep quality, and the
non-genetically modified mutant yeast strain discovered in this
study could be easily applied to brewing sake, a traditional
Japanese alcoholic beverage, as well as wine and beer.



FULL STORY ==========================================================================
Fans of sake, the traditional Japanese alcoholic beverage, may have
even more reason to enjoy it now: Japanese scientists have discovered
that a mutant strain of sake yeast produces high levels of the amino
acid ornithine.


==========================================================================
In a study published this month in Metabolic Engineering, researchers
from the Nara Institute of Science and Technology and the Nara Prefecture Institute of Industrial Development have revealed that a mutant strain
of sake yeast produces 10 times the amount of the amino acid ornithine
compared with the parent yeast strain.

Ornithine is a non-protein-making amino acid and a precursor to two amino
acids -- arginine and proline. It has been found to perform several physiological functions, such as reducing fatigue and improving sleep
quality.

"We wanted to obtain sake yeast strains with improved ethanol tolerance,"
says a first author of this article, Masataka Ohashi. "During sake fermentation, the yeast is exposed to high concentrations of ethanol,
which impedes yeast cell growth, viability and fermentation. Increased
ethanol tolerance in sake yeast strains could improve ethanol production
and reduce fermentation time." To find ethanol-tolerant yeast strains,
the researchers isolated mutants that accumulated proline, which can
alleviate ethanol toxicity, using a conventional mutagenesis (i.e.,
one that doesn't involve genetic modification). They also conducted
whole genome sequencing analysis, and performed brewing tests with sake
yeast strains. Then they identified and analyzed a new mutation in a
gene that encodes a variant of N-acetyl glutamate kinase that increases intracellular ornithine level.

"We previously constructed self-cloning industrial yeast strains that accumulate proline to increase ethanol tolerance and productivity of
yeast," explains Prof. Hiroshi Takagi, a corresponding author. "But
those yeasts have not been yet acceptable to consumers because they're considered to be genetically modified, even though a self-cloning yeast
has no foreign genes or DNA sequences -- they only have yeast DNA."
The researchers successfully isolated non-genetically modified yeasts
that produced 10 times the amount of ornithine compared with the parent
strain, which is widely used in Japanese sake breweries, and the sake
brewed with them contained 4-5 times more ornithine.

The results of this study will contribute to the development of improved
yeast strains for production of high levels of ornithine, and the strain obtained in this study could be readily applied to sake, wine, and beer brewing. Ornithine- accumulating yeast strains could also be used in
the production of ornithine- rich dietary supplements made from these
yeasts and their products.

Prof. Takagi also describes "There are two major purposes for breeding
of industrial yeast: improvement of fermentation ability with enhanced tolerance to environmental stresses during fermentation processes and
diversity of product taste and flavor with modified metabolic pathways. In yeast, amino acid metabolisms vary under different growth environments
and the metabolic styles form a complicated but robust network. The
elucidation of metabolic regulatory mechanisms and physiological roles
for amino acids is important fundamental research for understanding
life phenomenon. The yeast is reliable and safe in food production,
and thus the development of novel strains that overproduce 'functional
amino acids' such as ornithine, proline and branched-amino acids, would
greatly contribute to food-related industries."

========================================================================== Story Source: Materials provided by
Nara_Institute_of_Science_and_Technology. Note: Content may be edited
for style and length.


========================================================================== Journal Reference:
1. Masataka Ohashi, Ryo Nasuno, Shota Isogai, Hiroshi
Takagi. High-level
production of ornithine by expression of the feedback inhibition-
insensitive N-acetyl glutamate kinase in the sake yeast
Saccharomyces cerevisiae. Metabolic Engineering, 2020; 62: 1 DOI:
10.1016/ j.ymben.2020.08.005 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200827101812.htm

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