In this study, scientists have reported the discovery of a novel phylum of microorganisms in the deep critical zone, and they seem to play a crucial part in water purification.
The Critical Zone, which ranges from the treetops to 700 feet underground, "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," noted James Tiedje, a University Distinguished Professor Emeritus at Michigan State University.
These newly identified microbes were found in soil samples that had been collected in Iowa and China, where regions had relatively similar soil compositions, and went very deep underground. The samples were taken from as much as 70 feet (21.3 meters) underground. The investigators analyzed the genetic material in these samples in a metagenomic study.
This effort revealed a novel phylum that is a category of CSP1-3 microbes. The ancestors of these microbes probably lived in freshwater or hot springs millions of years ago, the researchers suggested. After at least one major transition, these microbes colonized soil, starting with topsoil and eventually moving deeper as the microbes evolved.
The microbes that were in the deep soil samples were also found to be alive. "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 novel microbes are not unusual and tend to actually dominate their communities, making up as much as 50% of the members in some cases. Surface soils, on the contrary, are far more diverse and not dominated by a single species.
"I believe this occurred because the deep soil is such a different environment, and this group of organisms has evolved over a long period of time to adapt to this impoverished soil environment," Tiedje suggested.
The CSP1-3 in deep soils also consume carbon and nitrogen, so they remove pollutants from water that washes down from the topsoil, which has already performed an initial purification step. "CSP1-3 are the scavengers cleaning up what got through the surface layer of soil," Tiedje said.
Now the researchers are interested in learning what else these microbes can do. First, they have to find methods to grow them successfully in the lab, which can be challenging because of the unusual nature of their native environments, and their preference for existing only in those places.
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