Flowers and seeds are a plant’s most visible asset, but the real action happens below the earth’s surface. A vast world of microbes in the soil do everything from providing nutrients to helping plants survive extreme drought. In the first large-scale analysis of this microbial microcosm, scientists led by HHMI Gordon and Betty Moore Foundation investigator Jeff Dangl looked at hundreds of types of bacteria that mingle with the roots of the mustard plant Arabidopsis thaliana.
To catalog the diversity of the root bacteria, Dangl and his team at the University of North Carolina at Chapel Hill, in collaboration with the Department of Energy’s Joint Genome Institute, planted more than 600 microbe-free seedlings in local soil samples. As the plants grew, the researchers analyzed the bacterial content of the roots and surrounding soil.
The resulting microbiome, published August 2, 2012 in Nature, showed that the soil close to the roots contains only a subset of all soil bacteria. Within the roots, even fewer types of bacteria settle in. This finding suggests that something is selecting which bacteria associate with the roots. “We don’t know if it’s the host’s ability to attract the bug or the bug’s ability to inhabit the niche, or both … but now we can do the analysis because we have defined conditions for reproducible experiments in this complex ecosystem,” says Dangl.