Wednesday, September 1, 2021

Glacial Ice Cores Reveal 15,000 Year Old Microbes

 

Extensive glaciation at high altitudes in the Tibetan Plateau.
Source: Reurinkjan
Known as the world’s “Third Pole”, the Tibetan Plateau holds a vast amount of Earth’s ice. Over 46,000 glaciers blanket the arid, elevated landscape, which is part of the expansive Hindu Kush Himalaya (HKH) mountain range. These mountains and their icefields collectively hold the largest volume of snow and ice outside the Arctic and Antarctic. One might easily assume that the ice is sterile and void of life beyond its inert composition, considering the ancient and inaccessible depths it descends to. However, a new investigation of Tibetan glacial ice cores reveals quite the opposite: these immense glaciers in fact hold a rich chronological record of frozen, unique microbial life.

Zhi-Ping Zhong is a postdoctoral paleoclimatology researcher at Ohio State University’s Byrd Polar and Climate Research Center, and the lead author of a new publication in the journal Microbiome outlining his team’s investigation of nearly 15,000-year-old microbes in Tibetan ice. Their innovation is in their methodology — it is notoriously difficult to isolate and preserve ancient microbial DNA well enough to resolve individual genomes, while simultaneously avoiding contamination or degradation of the sample. In addition, glacier ice contains very low levels of biomass, making contamination by today’s microbes and viruses an even more imposing risk. Zhong and his team pioneered a new approach that accomplished this difficult task with remarkable precision, permitting them to see right down to the ancient genes.

“We developed clean methods to remove the contaminants on glacier ice core surfaces,” Zhong explained in an interview with GlacierHub. “This helps guarantee we obtain the ‘real’ microbes and viruses that were archived in glacier ice, not contaminants.” The team’s methods involved meticulous shaving and disinfection of the cores down to their innermost ice, isolating relatively uncontaminated material for analysis. They expanded upon previous work by first validating their methods on artificial cores they had laced with known bacteria, allowing them to measure what amount of the mock contaminants remained. With more concrete data on the efficacy of their approach, they proceeded to clean and process the actual cores.

The ice cores used in the investigation were drilled by Lonnie Thompson and colleagues in 2015 from the Guliya Ice Cap. Thompson, a renowned paleoclimatologist and professor at Ohio State University since 1991, began (alongside Ellen Mosley-Thompson) building the Byrd Polar and Climate Research Center’s ice core collection several decades ago. Zhong emphasises that glacier ice does not only archive past climates and chemical information about Earth’s atmosphere — it also archives entire microbial ecosystems, providing a preserved biological record going back untold thousands of years. 

The research team’s meticulous contamination prevention and reduction methods both outside and inside the lab revealed certain groups of bacteria commonly found in glacier ice such as Janthinobacterium, Polaromonas, and Sphingomonas. However, investigation of viral genetic material uncovered entire genetic sequences which were unique to the study, revealing 28 novel genera. This rate of 88 percent novel genera found in the glacier ice is much higher than those found by viral analyses of ocean environments (52 percent unique genera) and soils (61 percent unique genera). Such discoveries at exceptional levels of detail are integral to Zhong’s goals for the study. He explains that he hopes to understand the mutation rates of microbes over long periods of time by comparing the frozen genomes with those of more current bacteria and viruses. “These efforts will provide us the possibility of using a sort of molecular clock to help date the ice.”

The potential applications of Zhong. et al’s methods don’t end on this planet, either. Extremophilic life on Earth (including hardy ice-dwelling bacteria and other microbes) are frequently studied as potential models for extraterrestrial life on other planets and moons. Numerous bodies in our solar system harbor water ice, albeit in more extreme climatic conditions, leading to the astrobiological assumption that such ice may be sufficient to provide habitable conditions for life. Because the team’s protocol was developed for microbial and viral extraction from high-elevation, cold, and dry environments on Earth, Zhong noted how similar techniques “may one day be applied in the search for life in the Martian polar regions as well in other icy worlds in our solar system.” 

These techniques hold great promise for expanding our understanding of microbial history and evolution, but alongside this field’s emergence comes the existential threat of climate change. A quarter of the Third Pole has melted since 1970, and according to a 2019 IPCC report, two-thirds of its glaciers are predicted to disappear within the next 80 years. These catastrophic trends are global to varying degrees, and with the melt comes the Earth-wide loss of a biological history going back hundreds of thousands of years, unsalvageable as these records transition to meltwater. 

Aware of this threat, the Byrd Polar and Climate Research Center has collected and preserved more than 7,000 meters of ice core sections over its 40 years of glacier ice analysis across the globe. The frozen room at the Byrd Center is a time capsule preserving histories of the world that soon may not be accessible anywhere else. Both the archived ice cores and Zhong’s methods may serve as a foundation for the next generation of researchers, working in a world where the only views of once magnificent and biology-rich glaciers are in shelved cylinders of ice, each four inches across and about a yard long. Scientists have barely begun to read the vast genetic tome that is contained in Earth’s glaciers — these new methods of recovering frozen genomes and preserving threatened ice are now facing a fruitful, fateful race against time.

Source/Credit: Columbia University Climate School / by Daniel Burgess

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