For most of my scientific career, my research has focused on yeasts. Firstly, those associated with food and beverage spoilage, then characterising species found in a diverse variety of contrasting habitats including Ecuadorian cloud forests and Antarctic glaciers, and most recently yeasts resident in the human gastrointestinal tract. Over the course of all this research, my favourite yeast has to be the budding yeast Saccharomyces cerevisiae, and not necessarily just from a scientific perspective.
Where does the name Saccharomyces cerevisiae come from?
You may know S. cerevisiae as either brewer’s yeast or baker’s yeast, depending on whether it is used for brewing, winemaking, or baking.
The name ‘Saccharomyces’ is Greek for ‘sugar fungus’, while the Latin-derived species epithet ‘cerevisiae’ means ‘of beer’, which taken together reflect this microbe’s fermentative capacity to quickly convert simple sugars such as glucose into ethanol and carbon dioxide.
Saccharomyces cerevisiae is also often referred to as ‘the budding yeast’, both by scientists and non-scientists alike. However, this is somewhat misleading, especially given that there are in fact many different species of budding yeasts in nature.
Here at the Quadram Institute we are home to the National Collection of Yeast Cultures (NCYC), which holds over 4000 different yeast strains, including a large collection of S. cerevisiae strains, for use in research and industry.
The first eukaryote genome sequenced
Well-known for its fermentative talents, in April 1996, S. cerevisiae made history.
This came about, when a laboratory strain of S. cerevisiae, known as S288C, long used by the yeast research community as a model organism, secured the prestigious honour of becoming the very first eukaryote to be fully genome sequenced. A eukaryote is an organism whose cells contain a nucleus.
The genome sequencing of this yeast was a truly international accomplishment. It involved more than 600 scientists from North America, Japan and Europe, and included former colleagues from the Institute of Food Research, Norwich.
Since this milestone was achieved more than 25 years ago, many hundreds of additional S. cerevisiae strains, collected from a wide variety of sources and habitats have been genome sequenced. With one of the biggest initiatives being the ‘1002 Yeast Genomes’ Project, which despite its original name culminated with the publication o1011 whole genome sequences!
Where does this yeast cerevisiae live?
Saccharomyces cerevisiae has been used by humans to make beer, wine and bread for thousands of years, with the earliest known records dating back to around 6000 BC and its use in beer brewing in ancient Sumeria and Babylonia.
As a result of this long association, coupled with the fact it is often found in fermentation-related environments like breweries, bakeries, wine cellars and vineyards, we used to think that S. cerevisiae was purely a domesticated species, restricted to human settings.
However, thanks to the collective efforts of a group of scientists, S. cerevisiae has since been found across the globe, from South America to Australasia, in a variety of wild habitats including cacti, oak trees and even soil.
In fact, in a recent large-scale field study across China, S. cerevisiae was found widely distributed in nature, including forests quite remote from human activity. Indeed, to date these Chinese isolates, from primeval forests, represent the most genetically diverged lineages of S. cerevisiae, providing tantalising clues as to a possible Asian origin of this species.
Finally, it turns out that S. cerevisiae can have a far more intimate association with us humans.
Some strains are pathogenic, meaning they can cause disease. They are relatively rare, and are typically found in patients with compromised immunity. These disease-causing strains can grow at a higher temperature (i.e. above 37°C), which could reflect possible adaptation to their human host.
Yet it appears that S. cerevisiae may not be restricted to just people who are immuno-compromised. This is best exemplified with the recent discovery of S. cerevisiae in the gastrointestinal tract of healthy adult Amerindians living in a remote indigenous community in French Guiana. This is in marked contrast to many Western industrialised countries, where Candida albicans is often the most common commensal yeast found living in people’s guts.
So, our close association with S. cerevisiae could go back further than we first thought and may even predate when our ancestors first began exploiting this highly fermentative fungus for brewing and baking purposes.
Image credit: NCYC