Mollivirus sibericum is a type of “giant virus” discovered after being preserved in a frozen state for thousands of years. Giant viruses are exceptionally large and can be observed with a standard light microscope, unlike most viruses that require an electron microscope. These large viruses represent a fascinating area of microbiology that challenges conventional understanding of viral size and complexity.
Discovery in the Siberian Permafrost
A French research team, led by Jean-Michel Claverie and Chantal Abergel, unearthed Mollivirus sibericum from a 30,000-year-old soil sample in the Kolyma lowland region of northeastern Siberia. This ancient ground, frozen since the Pleistocene epoch, proved to be an exceptional preservative, keeping the virus particle intact and dormant for millennia.
To determine if the ancient virus was still viable, scientists introduced the permafrost sample into a culture containing live amoebas, which they suspected were the virus’s natural target. The amoebas began to die, indicating that the virus had reactivated and was replicating. This marked the fourth time a prehistoric giant virus had been revived from permafrost since 2003 and was found in the same sediment that previously yielded Pithovirus sibericum.
Unique Characteristics of a Giant Virus
Mollivirus sibericum has a roughly spherical particle shape and measures approximately 0.6 micrometers in diameter. Its name, Mollivirus, translates to “soft virus,” a reference to its particular structure. This size is significant because it blurs the lines between the viral world and cellular life, approaching the dimensions of some small bacteria.
The most remarkable feature of this ancient virus is its genetic complexity. While a common virus like influenza might have around eight genes, Mollivirus sibericum has a genome that contains over 500 genes. This extensive genetic library provides the blueprint for 523 different proteins, which reduces its dependency on the host cell’s machinery and challenges the traditional definition of a virus as a simple, non-living entity.
The Life Cycle and Host
The life cycle of Mollivirus sibericum revolves around the single-celled organism, the amoeba Acanthamoeba. This common protist, found in soil and water environments globally, serves as the natural host. There is no scientific evidence to suggest that Mollivirus sibericum is capable of infecting humans or any other animals.
Once it infects an Acanthamoeba cell, the virus begins replicating in the host’s cytoplasm. It hijacks the cell’s internal mechanisms to produce new virus particles. One surprising finding is that the virus packages some of the host’s ribosomal proteins within its new particles, an unusual behavior that highlights the complex interactions between the giant virus and its host.
Implications of Thawing Permafrost
The revival of Mollivirus sibericum has significant implications regarding global climate change. Its ability to remain infectious after millennia of dormancy demonstrates that ancient microbes can survive being frozen. The primary concern is not about Mollivirus sibericum itself, but what it represents.
As global temperatures rise, the Arctic permafrost is thawing at an accelerating rate. This process is releasing organic material, greenhouse gases, and dormant microorganisms into the environment. The revival of this ancient amoeba virus suggests that other, unknown viruses could also be released, and scientists are concerned that some might be capable of infecting humans or animals.
This potential threat has spurred further research into the microbiology of permafrost. Scientists now use amoeba-infecting viruses as surrogates to study the risk safely. As industrial activities like mining and shipping increase in the newly accessible Arctic, the chances of encountering a previously unknown and potentially pathogenic virus also increase.