Public Release: 

A handful of bacteria dominate the Earth's soil globally

American Association for the Advancement of Science

An assessment of soils across six continents reveals that very few bacterial taxa are consistently found in soils globally. The work represents the first global atlas of soil bacteria - comparable to atlases of plants and animals that have been available for decades. Notably, a substantial portion of the dominant bacterial phylotypes identified in this assessment were genetically very distinct from known bacterial genomes, indicating how little is known about even abundant groups of bacteria. Soil bacteria play key roles in regulating terrestrial carbon dynamics, nutrient cycles, and plant productivity. However, the immense diversity of soil bacterial communities has made it difficult to characterize individual taxa and document their global distributions. A more comprehensive understanding of the most abundant bacterial taxa - and their environmental preferences - could allow scientists to build better models of how soil bacterial communities vary across space, time, and in response to anthropogenic changes. Here, Manuel Delgado-Baquerizo and colleagues analyzed soils from 237 locations across six continents. They found that only 2% of bacterial phylotypes (or 511 out of 25,224) were consistently identified in nearly half of the soil bacterial communities sampled. In other words, despite the overwhelming diversity of soil bacterial communities, relatively few taxa are abundant and those that are can be found across a wide range of soil types. When the researchers looked at more than a dozen environmental factors, they found that bacterial types could generally be grouped based on five key "preferences": high pH, low pH, drylands, low plant productivity, and dry-forest environments. The results of this study narrow down the immense number of bacterial taxa to a list of those that will be important targets for efforts aimed at improving understanding of soil microbes and their contributions to ecosystem functioning.

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