TU Delft researchers discover a yeast that does not need to breathe

Yeast that grows without oxygen? TU Delft biotechnologists dusted off a type of yeast that had been briefly described 50 years ago and that can perform this remarkable feat.

The relatively unknown yeast species Schizosaccharomyces japonicus could perhaps be used to make very good beer. (Photo: Helena Lopes / Unsplash)

It won’t be tamed easily and it forms crazy strands when shone upon with the tiniest bit of light. Still, biotechnologists Sanne Wiersma and Jonna Bouwknegt (Applied Sciences) have high expectations of this yeast, the Schizosaccharomyces japonicus. It could well be the future tool in the production of alcohol.

Sanne Wiersma: “It looks like the yeast has taken a gene from a bacteria. That is truly fascinating.” (Photo: Wiersma)
What is so special about it?

This little known yeast, that lives in fruit and the juices of plants, appears to have a gene which allows it to produce a substance, the equivalent of cholesterol for humans, that enables it to survive without oxygen. The researchers wrote about it in the scientific journal PNAS. Wiersma explains why japonicus’ trick is so amazing and so promising. (Read the interview beneath the picture).

We already have the baker’s yeast Saccharomyces cerevisiae to make wine, beer, bread and biofuels. What can Schizosaccharomyces japonicus give us?
“The yeasts that we now use in industry usually need oxygen to multiply. It would be useful to have microorganisms that do not need to breathe. Breathing microorganisms produce CO2 as a by-product when they burn sugar. They also generate a lot of heat, pushing up the costs of cooling.

Yeasts need oxygen to produce an important building block called ergosterol, the yeast variant of cholesterol. This substance strengthens cell membranes. Only a few types of yeast, including the baker’s yeast Saccharomyces cerevisiae, can absorb the molecule ergosterol from their food so you need to either feed the yeast the right nutrition or aerate it well in advance. Preferably, you wouldn’t do either.”

Enter Schizosaccharomyces japonicus.
“Right. This ‘beastie’ is not in the least bit interested in oxygen or ergosterol. It is able to produce hopanol, a substance that resembles ergosterol and fulfils the same role.”

It is not a completely new discovery, is it?
“A researcher from Wageningen described the phenomenon that Schizosaccharomyces japonicus can survive without oxygen. But the scientist did not look at how it did this. We discovered the gene that makes this possible.”

That must have been a euphoric moment.
“I was working with bacteria DNA which bacteria use to produce hopanol, but it was not working very well in baker’s yeast. Jonna found a gene in a database which allowed a different bacteria to produce hopanol. She checked if the Schizosaccharomyces japonicus genome had a similar DNA sequence. It transpired that it did. I remember her jumping around my desk with glee. Apart from the discovery having practical implications, it is in itself a very interesting discovery. It looks like the yeast has taken a gene from a bacteria. That is truly fascinating.”

And what is next for the research? People have been using baker’s yeast for hundreds of years. And certainly over the last few decades yeast has been completely adapted to the bio-industry.
“This is not yet the case with Schizosaccharomyces japonicus. Growing this yeast is hard as it forms fungus-like strands as soon as light reaches it. And the techniques to genetically modify this yeast are barely developed so we still have a way to go.”

What most people naturally want to know is if you will eventually be able to brew your own beer, japonicus beer.
Laughingly, Wiersma replies. “That’s a good idea. I’m not going to deny or confirm it!”

Editor Tomas van Dijk

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