Some are classified as Deuteromycota, if no sexual stages are known. Though humans have used yeasts to raise bread and ferment alcoholic beverages for thousands of years, only recently have they been separated into pure culture for more controlled human use. Saccharomyces cerevisiae is the most important of all domesticated fungi. Highly active metabolically, this ascomycete is available as baker's and brewer's yeast. Researchers use Saccharomyces to study eukaryotic molecular genetics because it is easy to culture and manipulate.
Some yeasts cause problems for humans.
Rhodotorula , a pink yeast, grows on shower curtains and other moist surfaces. Though lichens vary in shape and physiology, some shared general features characterize the symbiotic relationship. The alga, which is below the lichen's surface, Always provides the fungus with food.