By Associate Professor Peter Pollard.
There are not many biological entitles that have a worse image problem than the virus. These days the much-maligned virus takes the blame for everything from trashing the spring racing carnival to crashing our computers.
But the virus could actually be one of humanity’s best friends.
The virus is not a living organism, it’s a form of parasite that injects its own genetic material into a host cell ( e.g. bacteria or human cell) taking over the host metabolic machinery to make lots of copies of itself. We find around 50 viral copies are for every host cell infected. Then the host cell explodes in a shower of new viruses that go on to infect more cells from the same host. The cycle of infection and killing continues until most of the host cells are dead.
The vast majority of viruses don’t harm humans, in fact most are beneficial to us because they keep in check other bugs that want to get out of control. Although you can’t see them with your eyes viruses play a big part in the ecology of the plant. Viruses are every where; they are on and in everything. If you put all the viruses on earth end to end they would span father than our nearest sixty galaxies and together viruses on our planet weigh more the 75 million whales!
Viruses in our waterways
I have studied the role of viruses that live in water, and our research has revealed that there are particular, helpful viruses that target the bacteria that live in our rivers and lakes and dams.
Bacteria are living, breathing organisms that take in oxygen and release carbon dioxide, so if their population become too dense, the water can become anaerobic (oxygen-starved) so fish and other animals die.
Just like humans, bacteria are vulnerable to viral infection and death. In fact, in many cases it appears we must give credit to viruses for keeping bacterial populations under control.
Bacteria can also fight back as they have the ability to evolve defences against viruses, similar to the way a human immune system adapts. But the virus is just as clever, it also evolves a new infection strategy. So both bacteria and viruses are always at war but at the same time we find they need each other to survive. We have found when a virus can live inside the bacteria without killing it, then the bacteria cannot be attacked by other viruses. Furthermore, the bacteria lives longer and has more genes that give the host a survival advantage (this is called a latent viral infection). It’s a bit like the bacteria and virus are playing Russian roulette, if the bacteria becomes stressed the virus breaks out of the bacteria (killing the bacteria in the process) because it thinks the bacteria is going to die. When that happens the bacteria definitely dies.
It’s as if every living thing has it’s nemesis – the bacteria and viruses are constantly evolving new methods to outsmart each other, and this closed cycle of growth, infection and death keeps our rivers healthy. Everything is balanced.
Associate Professor Peter Pollard a microbial ecologist with Griffith’s Australian Rivers Institute.