Published: 8 May 2020, 07:00 | By: Ute Schönfelder
During the corona pandemic, most people probably see viruses as dangerous pathogens. However, the tiny infectious particles play an important part in very different ecosystems and regulate global cycles. In this interview, bioinformatician Prof. Dr Manja Marz and chemist Prof. Dr Georg Pohnert shed light on the roles of viruses in nature.
Where in nature are viruses found?
Marz: Wherever there are organisms, there are viruses; they need host organisms in order to replicate. This means that we also have viruses inside our bodies—in our intestines, for example. Viruses are found in the air, in waters, but also on our keyboards, and in our beds.
Are there reliable numbers or estimates of how many species of viruses exist?
Marz: There are approximately 3,500 known species of viruses—although, biologically speaking, viruses are no “species”, because they are not classified as living organisms. They only consist of wrapped-up genetic material: DNA or RNA. In order to duplicate, they have to enter the cells of a host organism and hijack their machinery (see infobox 1). However, more than 99 percent of all virus species are still unknown. Our body contains ten times as many bacteria as human cells; and there are also ten times as many viruses.
Which viruses do you study in your work as scientists?
Marz: In 2017, we founded the European Virus Bioinformatics Center, which has since had its seat at the University of Jena (see infobox 2). The centre deals with bacteriophages—viruses that replicate within bacteria—but also with other DNA and RNA viruses. Our working group mainly investigates RNA viruses, which include SARS, MERS and other coronaviruses; but we also research Zika, Dengue, yellow fever, hepatitis C, influenza and Ebola viruses.
Pohnert: We study viruses in oceans that infect unicellular algae like the coccolithophore Emiliania huxleyi. In open ocean waters, microalgae form the base of the marine food web and account for almost half of the global photosynthesis. They absorb carbon dioxide and release oxygen. This means that the global climate and our nutrition depend on these algae. Specialized viruses such as the Emiliania huxleyi virus 86 can infect these algae and destroy them. In our research, we deal with the mechanisms of this viral infection and look for mechanisms of resistance.
What happens if viruses infect algae in oceans?
Pohnert: When viruses infect algae, they enter their cells and completely reprogramme their metabolism. Biochemical metabolic pathways that the algae usually use at a very low rate are activated; and the algae then produce components for the viruses’ capsids. Once the number of viruses reproduced in the algae’s cells is high enough, lysis is induced; the algae burst, releasing a huge number of viruses ready to infect algae themselves and thus extinguishing entire populations.
This sounds like a rather one-sided partnership.
Pohnert: The virus infection obviously kills the individual algae cells. As a result, however, the viruses fulfil a vital function in the ecosystem. We have to bear in mind that a complex community of microorganisms is coexisting in the ocean, one that is constantly changing. When these specialized viruses reduce one algae species in the ecosystem, they create space for another species of algae to proliferate. In addition, viruses do not kill all individuals of a species; some cells are always more resistant and will be able to proliferate later in the year or in the next season. Viruses play the role of regulators, making sure that there is a healthy mix of species.
Viruses are also found in groundwater. Should we worry about that?
Marz: No, I don’t think so. Only a very small fraction of viruses is pathogenic for humans. Most viruses—more than 99 percent or so—are not virulent, but necessary for marine ecosystems for example, as we have just heard. It is believed that viruses regulate not only unicellular algae, but also bacteria living in water—in the groundwater, for example. The exact composition of the viruses in the groundwater is still unknown, but one thing is already clear now: Without viruses, the bacterial composition of groundwater would be entirely different.
Can we say that viral infections are a common way in nature to regulate the growth of microorganisms?
Pohnert: Yes, and not only of microalgae. Numerous bacteriophages—viruses that attack bacteria—have a regulatory effect on microbial communities; but viruses can be found in all multicellular organisms. Many plants are infected by viruses such as the tobacco mosaic virus, which causes the leaves to change colour and leads to a poor harvest. Livestock are also affected by viruses. They are closely monitored in order to contain possible outbreaks.
Marz: Viruses also play a very big role in human gut microbiome. Researchers at Jena University Hospital investigate the causes of gastrointestinal diseases and the role played by viruses. For this purpose, Prof. Dr Andreas Stallmach’s working group carries out fecal transplants. Together with his group, we are trying to gain a better understanding of the role viruses play in stool.
Are there results from your virus research that can be transferred to the current corona pandemic?
Marz: Coronaviruses, similar to other respiratory viruses (e.g. influenza), spread in small airborne droplets. The higher the humidity during a season, the longer the viruses circulate before they stop replicating. If the climate now becomes warmer and dryer, it might have a rather adverse effect on the viruses. In a joint project with virologists from the University Hospital, we are trying to determine the half-life of RNA viruses in liquids.