Unveiling the Secrets Below: Exploring a Mysterious New Bacterial Phylum That Thrives Underground

The soil beneath us is full of life, possibly more than any other place on Earth. Recently, scientists discovered a new group of bacteria, called CSP1-3, thriving in the dark depths of our planet’s soils. This phylum was first seen in 2006 in Yellowstone’s geothermal areas, and since then, researchers found its relatives in various deep soil environments, like tropical rainforests and iron-rich subsurface soils.

A global team has now assembled an extensive genomic catalog of these bacteria. Their research reveals that CSP1-3 bacteria are not merely dormant; they are alive and slowly growing. Microbiologist James Tiedje from Michigan State University explains that these organisms are adapting well to their underground habitats where they feed on carbon and nitrogen filtering down from the surface.

In deep soils, CSP1-3 is dominant, making up 60% of the microbial community in some areas, which is quite unlike surface soil populations. Tiedje notes that deep soil presents a unique environment, one that has influenced these microbes to evolve over time.

Even with the lack of nutrients, deep soil ecosystems are surprisingly diverse. While surface soil hosts denser microbial communities, the total number in deep soil remains similar—it’s just that those microbes are more spaced out.

Researchers found that all CSP1-3 members might utilize aerobic carbon monoxide oxidation, which helps them survive when nutrients are scarce. They also show potential for hydrogen metabolism, both of which are essential energy sources in nutrient-poor soils. This flexibility may give them an edge in survival.

In their genomic study, Tiedje and his international colleagues also tracked one lineage of CSP1-3 that once thrived in water before making the leap to land. It likely picked up genes that help it manage energy and carbohydrates. However, many questions remain about this bacterium’s role, ecological importance, and evolutionary path.

Interestingly, over 99.999% of Earth’s microbes have yet to be identified. Of the trillions of species believed to exist, more than 90% are thought to live below the soil surface. CSP1-3 is just one of many undiscovered mysteries.

Tiedje likens these bacteria to “scavengers” cleaning up what passes through the soil’s upper layers. As researchers aim to cultivate the CSP1-3 microbes in the lab, we’re on the verge of a deeper understanding of their functions, the ecosystems they inhabit, and the intricate web of life that exists just beneath our feet.

This study sheds light on the critical role microbial life plays in ecosystems, highlighting that understanding these hidden organisms can reshape our knowledge of soil health and biodiversity. For more on the findings, you can check the full study published in PNAS.

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