Water Clean-Up Crew

Deep beneath the soil, there is another world, with creatures busy cleaning up nature.  

Now, a new study is providing fresh details about this region, part of what is known as the Critical Zone that is essential to the Earth’s “living skin,” where a previously unknown type of microbe helps purify water.  

“The Critical Zone extends from the tops of trees down through the soil to depths up to 700 feet,” study contributor James Tiedje explained. “This zone supports most life on the planet as it regulates essential processes like soil formation, water cycling, and nutrient cycling, which are vital for food production, water quality, and ecosystem health.” 

Despite its crucial role, the deep Critical Zone remains largely unexplored.  

In this huge, mostly unknown microbial world, researchers found a completely different phylum – a term indicating a classification level in biology – of microbes called CSP1-3. 

The new phylum was found in soil samples from Iowa and China at depths down to 70 feet. The provenance of the sample was based on the fact that Iowa and China have very deep and similar soils, and researchers wanted to know if CSP1-3 occurrence is general or confined to one area. 

Analyzing the DNA extracted from the deep soils, the team found that CSP1-3’s ancestors lived in hot springs and in freshwater millions of years ago. Over time, they went through at least one major habitat shift, first colonizing topsoil and later deep soils.  

“Most people would think that these organisms are just like spores or dormant,” said Tiedje. “But one of our key findings we found through examining their DNA is that these microbes are active and slowly growing.” 

The newly discovered organisms are not rare members of the community but are dominant, making up 50 percent or more of the community in certain cases, a rare event in surface soils. 

Soil acts as Earth’s biggest filter: When water goes through it, it gets cleaned by physical, chemical, and biological processes.  

The surface soils, where most plant roots are found, are a relatively thin layer in which rainwater passes through quickly.  

Meanwhile, deep soil has a much larger volume, and this is where CSP1-3 microbes come in.

Feeding on carbon and nitrogen that is washed down from the topsoil, they help complete the natural purification process. 

“CSP1-3 are the scavengers cleaning up what got through the surface layer of soil,” Tiedje said. “They have a job to do.”