Answer to the Friday Whatsit for November 12, 2010
I thought for sure someone would get the Whatsit this week, but no one guessed that the avocado-shaped objects in this week’s image were. They are members of the Kingdom Fungi, which includes mushrooms, molds and . . . yeasts! These are Saccharomyces cerevisiae, commonly known as baker’s yeast, brewer’s yeast or budding yeast.
Yeasts like S. cerevisiae take in sugars and produce ethanol and carbon dioxide gas in a process called fermentation. The CO2 gives lift to bread and fizz to beer and the ethanol gives beer, wine and distilled spirits their alcoholic content. Some even eat the spent yeast and such in the form of Marmite/Vegemite spread, although I wouldn’t recommend this, taste wise.
In addition to their contributions to food, yeasts are well known in the scientific and medical worlds. S. cerevisiae and Schizosaccharomyces pombe (fission yeast) are important model organisms in biology, in part because they are simple eukaryotic (nucleated) cells. They are used mainly for experiments trying to work out the genes and proteins involved in the cell cycle and the mechanics of cell division. They are also used in the yeast two hybrid assay, a process used to investigate protein to protein or protein to DNA interactions.
Members of the yeast genus Candida (most often Candida albicans) are normally found living in a mutually beneficial relationship with our digestive system. Their numbers are held in check by normal human gut bacteria and our own immune system. However, in situations where normal gut bacteria or the immune system are compromised (such as when taking antibiotics or when in an immunocompromised state) these yeasts can grow out of control and become a health risk. We experience candidiasis in many forms, including thrush, reproductive or urinary tract infections, and even life-threatening systemic infections.