Saccharomyces cerevisiae

Saccharomyces cerevisiae (Latin for "sugar-mold (of) beer") is a species of yeast, a type of fungus. It has been used commercially since ancient times in making wine, bread and beer. 
In biological research, it is the most studied type of yeast and is as well understood as E. coli. Many biological processes and organic molecules common to most forms of life were first identified in saccharomyces. It is currently being studied in an attempt to understand the mechanism of aging, to determine the mechanism by which DNA repairs itself, to understand the workings of genes, and in astrobiology research. 
As it produces carbon dioxide as a by-product of its metabolism, it is used by some aquarium owners to raise the level of carbon dioxide in water for use by plants without the use of expensive gas cylinders. 
Saccaromyces cerevisiae at Wikipedia