Non-motile single-celled fungi used here to study bubble-driven dispersal in gels.Yeasts are single-celled fungi that live as individual rounded or oval cells rather than as moulds or mushrooms. They are not motile — they have no flagella or other means of swimming — and they reproduce mainly by budding, in which a daughter cell grows out of the parent and pinches off. The best-known species, Saccharomyces cerevisiae, is the organism behind bread rising and beer fermenting, but yeasts are also ubiquitous in soil, on plant surfaces and on human skin.
In research, yeasts are a workhorse model organism. They grow quickly, are cheap to culture, can be kept as stable haploid or diploid strains, and their genetics can be manipulated with unusual ease. Many fundamental discoveries about how cells divide, repair DNA and manage their metabolism were first made in yeast and later found to apply to human cells. Because yeast cells are non-motile, they stay where they are placed, which makes them convenient for experiments on how populations spread through a material by growth and division rather than by swimming.
In the context of bubble-driven dispersal in gels, yeast serves as a living tracer: cells embedded in a gel can be carried outward when bubbles grow, merge or move through the matrix. This lets researchers study how mechanical disturbance redistributes a population that cannot propel itself, a question relevant to how microbes colonise soft materials and how bubbles transport particles in foods, foams and biological tissues.
Yeast has been used by humans for at least several thousand years in brewing and baking, long before anyone knew it was alive. Antonie van Leeuwenhoek first observed yeast cells under a microscope in the 1680s, and in the 1850s Louis Pasteur demonstrated that fermentation is caused by living organisms rather than by purely chemical decay. Saccharomyces cerevisiae became a laboratory model in the twentieth century and was the first eukaryote to have its genome fully sequenced, in 1996.
A yeast cell grows by bud formation: the cell wall softens at one spot, a new cell emerges, and the nucleus divides so that one copy goes to the bud before the two cells separate. Growth is fuelled by fermentation of sugars, producing ethanol and carbon dioxide — the gas that leavens dough and carbonates beer. In a gel experiment, the yeast cannot swim, so any displacement of cells must come from the surrounding material. When a bubble nucleates and expands, it pushes the gel aside; when bubbles coalesce or rise, they drag the matrix and any embedded cells with them, spreading the population along the path of the bubble.
Beyond brewing and baking, yeasts produce industrial ethanol and recombinant proteins such as insulin and vaccines, and they serve as the standard model organism for studying eukaryotic cell biology and genetics.
Yeast and humans share a striking number of genes: roughly a third of yeast genes have a recognisable human counterpart, which is why studies of yeast cell division have repeatedly illuminated human cancer biology.
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