Yeast is not a bacteria, it is a eukaryotic microorganism from the Fungi kingdom. It is a unicellular organism found in soil, water, plants and on the skin of humans and animals. It reproduces asexually through a process called budding. There are 1,500 species of yeast.
Yeast is commonly used in baking, beer brewing and wine making. It has used been for this purpose for thousands of years, and evidence of bakeries and breweries has been found in ancient Egyptian ruins. Saccharomyces cerevisiae is the species of yeast that is most commonly used for these purposes. When conditions are less than ideal, yeast reproduces sexually by fusing together with other yeast cells.