We may not see them, but we need them. iStockphoto.com hide caption

itoggle caption iStockphoto.com

Streptococcus bacteria, like this strain, can be found in our guts. Janice Haney Carr/CDC Public Health Image Library hide caption

itoggle caption Janice Haney Carr/CDC Public Health Image Library

Fungi (cyan) surround a human hair within the skin. A study in the journal Nature shows the population of fungi on human skin is more diverse that previously thought. Alex Valm, Ph.D. hide caption

itoggle caption Alex Valm, Ph.D.

Yeast affects several aspects of beer including the foam, or head, that forms on the of the glass. If fermentation is too vigorous, too many of the foam-stabilizing proteins may be lost. Cate Gillon/Getty Images hide caption

itoggle caption Cate Gillon/Getty Images

Twins in Malawi helped scientists discover a role the gut microbiome appears to play in severe malnutrition. Photograph courtesy of Tanya Yatsunenko hide caption

itoggle caption Photograph courtesy of Tanya Yatsunenko