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Leonardo da Vinci once remarked that our understanding of celestial movement far exceeds our knowledge of the soil beneath us.
James Tiedje, a microbiology expert at Michigan State University, echoes this sentiment. He is committed to enhancing our comprehension of the Critical Zone, an essential part of Earth’s dynamic “living skin.”
“The Critical Zone stretches from the treetops down to soil depths of up to 700 feet,” Tiedje explained. “It plays a crucial role in sustaining life on Earth by managing vital processes including soil formation, water cycling, and nutrient cycling. These processes are foundational for food security, water quality, and overall ecosystem health. Despite its significance, much of the deep Critical Zone remains uncharted territory.”
Exploration of the Deep Critical Zone
Tiedje, recognized as a University Distinguished Professor Emeritus in the Departments of Microbiology, Genetics and Immunology, as well as Plant, Soil and Microbial Sciences at MSU, has uncovered a novel phylum of microorganisms designated as CSP1-3. This phylum was identified in soil samples taken from depths of up to 70 feet in both Iowa and China, regions known for their deep and comparable soil profiles. “We are interested in determining if this discovery is applicable beyond these specific locations,” Tiedje said.
His research team extracted DNA from these deep soil samples and traced the ancestry of CSP1-3 back to aquatic environments—specifically hot springs and fresh water—over millions of years ago. They observed that these microorganisms had transitioned through significant habitat shifts, first adapting to topsoil and eventually colonizing deeper soil layers throughout their evolutionary journey.
Crucially, Tiedje noted the active nature of these microbes. “Many might assume these organisms are dormant or simply spores,” he stated. “However, our analysis of their DNA reveals that they are indeed active and exhibiting slow growth.” Moreover, he was taken aback to find that CSP1-3 are not merely minor constituents of the microbial community; in fact, they can represent over 50% of the microbial population in deep soils, a stark contrast to typical surface soils.
“I believe this prevalence arises because deep soil presents a markedly different environment, leading this group of organisms to develop adaptations over extensive evolutionary periods,” Tiedje added.
Microbial Role in Water Purification
Soil functions as the largest water filtration system on the planet. As water permeates through soil layers, it undergoes various physical, chemical, and biological purification processes. While surface soil, which hosts most plant roots, constitutes a relatively small volume, the deeper soil layers encompass a significantly larger volume. This is where microbes like CSP1-3 play a crucial role. They utilize carbon and nitrogen that filter down from the upper soil layers to facilitate the water purification process.
“CSP1-3 act as scavengers, effectively cleaning up what filters through the surface layer of soil,” Tiedje remarked. “They have an important role to fulfill.”
Future Research Directions
Looking ahead, Tiedje indicated that the next phase of research would involve culturing these microbes in laboratory settings. Successfully growing them could allow for deeper insights into their unique physiological attributes that enable survival in deep soil ecosystems. However, this task is fraught with challenges, as many microorganisms remain uncultured due to the difficulty of mimicking their natural growth conditions.
Given that the ancestors of CSP1-3 thrived in hot springs, Tiedje’s lab plans to attempt cultivating them at higher temperatures as a means of simulating their natural environments based on genomic data.
With a track record of previous discoveries, including microbes capable of dechlorinating harmful chemicals, Tiedje is optimistic. “CSP1-3’s distinct physiology, informed by their unique biochemistry, may uncover some intriguing genes with potential applications,” he noted. “For instance, understanding their abilities to metabolize challenging pollutants could contribute to addressing some of the most critical environmental issues we face today.”
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