15000-year-old Microbes discovered in Tibetan glacier ice

Srabani Roy Chowdhury (MAKAUT, WB)

Glacier ice provides microbiological information that helps in predicting future climate changes and study paleo-climatic history. According to microbiologists, the bacteria and their phages (or bacteria infecting viruses) found in the Tibetan glacier ice are likely to be originated from soil or plants. These identified microbes are said to represent atmospheric microbes during their time of deposition.

The most dominant bacterial phyla found under the ice are Proteobacteria, Actinobacteria, Firmicutes, and Bacteroidetes. Among various records of microbes found under glacier ice, there have been only two reports showing viruses found under ancient glacier ice. One reported virus-like particles using Transmission Electron Microscopy under Vostok glacier. The other one was atmospheric tomato mosaic tobamovirus RNA reported using reverse transcription PCR under Greenland glacier ice.

Study Records:

Microbiologists studied two Tibetan plateau glacier ice cores that aged around 15000 years. Samples from eight layers were sent for amplicon sequencing. It revealed the presence of some dominant genera like Flavobacterium, Herminiimonas, Janthinobacterium, Polaromonas, Sphingomonas, and Methylobacterium. But there were significant differences between the microbial communities present in the two ice cores. These determine that the climatic history during their deposition was also different. Viral enrichment of the glacier ice cores was also studied. Low-input quantitative sequencing of the ice cores with different ages (14400 years v/s 355years) was carried out. This sequencing report provides the first evidence of viral genome fragments from the environment in the ice cores. In accordance with the studies conducted, it has been found that:

• Significantly different microbial communities were found in different ice cores and depths with the 26 most abundant genera.
• Most of the viral communities found in the ice cores belong to novel genera. They differ in their frequency in different depths. Results also indicate that the ice cores contain a significant variety of unique viruses as well.
• Prediction states that there are chances of the glacier ice microbes getting infected by the viruses present there at some time. It also states that this prediction might also play an important role in shaping and modulating microbial communities.
• The Glacier ice environment is likely dominated by temperate phage viruses. Extreme environmental conditions influence the frequency of temperate viruses since they tend to be more abundant under extreme conditions than virulent viruses. So they can remain frozen under the glacier ice for a very long period.
• Viruses found in the glacier are found to influence host chemotaxis. Virus-encoded Auxiliary Metabolic Genes (AMGs) are reported in the studies associated with the glacier viral community. These genes are capable of modulating host metabolism.

Conclusion:

The rapid melting of these glaciers might destroy these archives of microbes and viruses. But, it might also release them into the environment creating a potential threat to mankind. This study reveals primary glimpses of the presence of microbial and viral communities in the glacier ice from the Tibetan plateau, which is nearly 15000 years old. The microbiological findings opened a wider aspect for the communities present, their genomes, functions, and origin.

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Reference: Zhong, Z.-P., Tian, F., Roux, S., Gazitúa, M. C., Solonenko, N. E., Li, Y.-F., Davis, M. E., Van Etten, J. L., Mosley-Thompson, E., Rich, V. I., Sullivan, M. B., & Thompson, L. G. (2021). Glacier ice archives nearly 15,000year-old microbes and phages. Microbiome, 9(1), 160. https://doi.org/10.1186/s40168-021-01106-w

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