American Scientist

Scoop up a tablespoon of soil from your backyard. In just that tablespoon, there could be more than 10,000 species of bacteria wriggling around. In the backyard down the street, or in the next town, or three counties away, the same tablespoon might pick up 10,000 completely different species of bacteria. Until now, there hasn't been a comprehensive map of soil bacteria. But a team of scientists, led by Manuel Delgado-Baquerizo, recently took the first steps toward creating one—and found out something surprising along the way.

These researchers collected nearly 300 soil samples from 18 countries (purple dots above) and as many different environments as possible, such as deserts, rainforests, and grasslands. They were expecting to find a diverse array of bacteria species spanning these different terrains.

Instead, the scientists found that across the many different environments on Earth, a small percentage of bacterial taxa dominated. About 2 percent of all bacterial taxa (or 500 individual species) dominate nearly half of Earth's environments. What's more, only about 20 percent of those 500 species are known to scientists. The rest still need to be studied and identified.

With this new "most wanted" list, scientists have a starting point for studying the complex web of any given ecosystem, said Noah Fierer, one of the coauthors of the global bacterial map and an ecologist at the University of Colorado in Boulder. But why do we care anyway?

These tiny organisms, which populate every environment from the hottest deserts to the coldest tundras, help many of Earth's processes progress. They create acidic environments that weather rocks, they decompose dead organisms and release gases such as carbon dioxide and methane into the atmosphere, and they help plants take up nitrogen, aiding plant productivity.

Fierer compared the project with studying a redwood forest. If you want to understand the relationships between organisms in the forest, you start with the most visible member of the ecosystem: the redwoods. In this case, studying these microbes that show up all over the world would be the first step to understanding the environmnet. For Fierer, the microbes on the new "most wanted" list are the redwoods of soil bacteria.

Reference

Delgado-Baquerizo, M. et al. 2018. A global atlas of the dominant bacteria found in soil. Science 359:320-325.