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Hidden world: The glaciers of the high mountains and polar regions are home to a still largely unrecognized world of microbes. More than ten thousand viruses that researchers have discovered in glacier ice, meltwater and dust on the ice surfaces now bear witness to this. These viruses primarily attack bacteria and are therefore harmless to us. However, many of them contain resistance genes that they can transfer to bacterial pathogens, as the team reports.
The ice of the glaciers and permafrost areas acts like a gigantic freezer and, in addition to numerous fossils and their DNA, also preserves the survival stages of many living organisms and viruses. Scientists have already managed to bring 700-year-old viruses, some rotifers that were frozen for 24,000 years, and a nematode that was preserved for 46,000 years back to life. Active viruses have also been detected on the surface of glaciers and in meltwater ponds.
Number of newly discovered glacier viruses by region. © Science China Press
Samples from glaciers worldwide
However, how many microorganisms actually live in the icy glacier environment is only partially known. It is therefore unclear how high the risk is, for example, of the resurrection of ancient pathogens from the ice. Now a new survey of the world of viruses on and in glaciers is providing more clarity.
For their study, Yongqin Liu from Lanzhou University in China and her colleagues took and examined samples from the ice, snow, meltwater and dust deposits on 38 glaciers in the high mountains and polar regions. “This provides the first systematic characterization of the diversity, function and potential health threat of polar and montane supraglacial viruses,” the team writes.
More than ten thousand species of DNA viruses
In the glacier samples, the researchers identified the genomes of around 10,840 types of DNA viruses – that’s a 15-fold greater variety of such viruses than was previously known, as Liu and her colleagues report. Despite the icy, rather hostile environment, these viruses were quite active: their reproduction rate corresponded to that of viruses in the ocean or in southern water lakes, as measurements on site showed.
The good news, however, is that more than 83 percent of the newly discovered glacier viruses are bacteriophages. These viruses specialize in infecting bacteria and therefore do not pose a direct threat to humans or animals. “The supraglacial viruses were highly specific compared to viruses from other habitats,” report the researchers. The risk to public health is therefore low.
Viruses transfer genes to bacteria – including resistance genes
However, a large proportion of glacier viruses in ice and snow are lysogenic, as the team discovered. This means that these viruses do not immediately destroy and kill their bacterial hosts. This means that infected bacteria continue to live for quite a while. This often results in the transfer of genes from the viral genome into the genome of the host bacteria – with both positive and negative consequences.
“The supraglacial viruses have the genetic potential to improve the cold adaptation, metabolism, cell mobility and phenolic carbon utilization of their hosts under these hostile conditions,” explain Liu and colleagues. On the other hand, the glacier viruses also transfer genes to the bacteria that give them resistance to antibiotics, as the analyzes showed. In total, the researchers identified 31 unique resistance genes and 1,405 virulence-encoding genes – genes that can increase the pathogenic effects of bacteria.
“Our study highlights that supraglacial viruses are numerous and active in glacial ecosystems,” state Liu and her team. “These viruses play a defining role for the supraglacial microbial communities.” It is therefore important to further investigate these viral and bacterial habitats. (Science Bulletin, 2023; doi: 10.1016/j.scib.2023.09.007)
Source: Science China Press
January 2, 2024 – Nadja Podbregar
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