A new toxic phenomenon: yeast is not a simple microorganism that we have always thought of

These findings reveal a selfish side of
yeast behavior.

A recently discovered phenomenon known as "latecomer killing" describes how yeast kills its own clones and other nearby microbes to survive
when it lacks glucose.

Yeast is not a simple single-celled microbe as we have always thought of, but a competitive killer
.
When yeast lacks glucose, it releases a toxin that can kill any other microbes that enter its habitat, even its own clones
.
This previously unknown toxic phenomenon has increased our understanding of
single-celled microbial behavior and the evolution of single-celled organisms to multicellular organisms.
It also has potentially valuable uses
in the food industry.

Baking bread became popular as a new pastime during the pandemic, so now you may find a small packet of dried yeast
hidden in many kitchen cupboards.
This tiny, live fungus has been an important part of our diet for thousands of years, allowing us to enjoy fluffy bread, sweet wine, and sparkling beer
.
Yeast was previously thought to be a simple, single-celled microbe, but now researchers at the University of Tokyo have demonstrated that it has a lethal survival strategy
.

There are more than 1500 known yeast species
.
Some are necessary for roasting and brewing, while others can cause infections
that affect human and animal health.

Tetsuhiro Hatakeyama, assistant professor at the Graduate School of Arts and Sciences, explains: "In the critical survival scenario of glucose starvation, yeast releases toxins into their habitat, killing other microbes, while yeast itself acquires
resistance.
We call this phenomenon late homicide
.
What surprised us even more was that the toxins produced by yeast can also kill clones they are not adapted to, so they not only risk killing invading microbes, but also killing their own offspring
.
This seemingly dangerous and near-suicidal behavior has never been found in single-celled organisms before and is even thought to be non-existent
.
”

While many bacteria and fungi exhibit cooperative behavior, this study is the first to detect competition
in clonal cells of single-celled organisms.
This gives us an understanding of microbial ecology and why some microbes grow during fermentation while others do not
.
To make this discovery, the researchers cultured cloned cells (from the same parent cells)
under glucose-restricted and glucose-rich conditions, respectively.
When these cells bonded together, growth patterns showed that yeast cells that had adapted to glucose starvation could poison latecomers while preserving food resources
for themselves.

Yeast cells poisoned by toxins produced by cloned cells
.
Dead cells are labeled
with dyes.

"Our study reveals a selfish side of yeast behavior," Hatakeyama said
.
"The phenomenon we found is similar to a thought experiment proposed by the ancient Greek philosopher Cyrene Kaneades, known as the plank of Caneades: If a sailor grabs a plank that can only support one person to escape from a shipwreck and then pushes away another sailor who is following him, will he be charged with murder?"

The researchers believe that this strategy may help yeast avoid mass starvation, while also helping to select toxin-producing offspring that are more likely to continue their lineage
.
This strategy was observed in several different types of yeast – originally extracted from beer, bread and wine – which could mean that the phenomenon may be more
widespread in this different species.

This discovery could be used to develop growth control mechanisms for economically important yeast species, such as yeast
used in the food industry.
While not included in this study, it may also pave the way
for better control of yeast types that can negatively affect human and animal health.
The team will next explore the implications
of this discovery for cell evolution.

Hatakeyama explains: "For the development of multicellular organisms, it is necessary not only to mutually activate cell growth, but also to mutually inhibit cell growth or programmed cell death
in cloned cells.
It is well known that fungi are more prone to evolutionary transitions between unicellular and multicellular organisms than other organisms, so we wanted to unravel the relationship between
afterkill and multicellular organism evolution.
"We hope that this research will make a significant contribution
to our understanding of ecosystem development and evolutionary transitions.
"

References: Autotoxin-mediated latecomer killing in yeast communities" by Arisa H.
Oda, Miki Tamura, Kunihiko Kaneko, Kunihiro Ohta and Tetsuhiro S.
Hatakeyama, 7 November 2022, PLOS Biology.