May 8, 2012Posted by srstone in Biology, Evolution, Genetics, Health, Medicine, Science Education.
Viruses: Friend or Foe?
What is invisible to the naked eye, can affect the Earth’s climate, has a tiny shell, and can causes cancer? Viruses are considered non-living, but play a major role in our bodies and environment. In fact, viruses kill half of the bacteria in the ocean every day. To get an idea of how much bacteria that is, a teaspoon of water contains approximately a billion bacteria. Recent estimates show there are 1031 viruses on this earth. That reads, 10 billion trillion, trillion. Although viruses are smaller than what the unaided eye is capable of viewing, if all viruses were stacked end to end, they would be lined up for about 100 million light years.
Viruses are constantly on the attack from the outside of our body desperately trying to get in, but 4 trillion viruses also reside inside our body. While some viruses are trying to find a host cell and cause harm, many viruses are necessary for a healthy life. Some of the viruses inside of us can protect us from detrimental bacteria, but can also help balance the population of bacteria vital to our health. A similar phenomenon occurs in the ocean. Without viruses consuming half of the bacteria day in and day out, the levels of bacteria in the ecosystem could hamper the living of certain species. Also, bacteria contain carbon and lots of nutrients. With the viruses consuming the bacteria, there is a constant recycling throughout the ocean. There is a hypothesis that because of all the carbon that’s coming out, it could be affecting the Earth’s climate. Any of the carbon that is sent back to the atmosphere is going to trap heat (greenhouse effect). It may be an extreme thought, but these tiny, non-living viruses are partially responsible for the weather.
Bacteriophages: the lifeless killers
Viruses that attack and dispose of bacteria are known as bacteriophages. Felix d’Herelle discovered the extraordinary conclusion that viruses can kill bacteria through treating a dish of bacteria with fluid from patients with dysentery! He actually began a business selling viruses that could cure bacterial infections. Hypothetically, there are viruses that exist in nature that can kill the most severe bacterial infections, but it’s a matter of discovering the right viruses. Each species of bacteria has a series of bacteriophages that can eliminate it.
Antibiotics and Viruses: An evolutionary arms race
Before antibiotics were discovered in the 1930s, a method called phage therapywas used to combat infections. However, once these antibiotic “magic pills” were discovered, phage therapy stood in the distance. The chemicals were reliable and scientists knew how to make them. However, with the current widening spread of antibiotic resistance caused by bacteria developing resistance to modern medicine’s most well-used antibiotics, it’s beginning to look like phage therapy wouldn’t be a terrible idea. One main argument phage therapy new found interest: antibiotics can’t evolve, while viruses can. Scientists have reached the point where viruses can be engineered and genes can be strategically placed to enhance their effectiveness. This genetic and evolutionary tinkering could allow scientists to develop viruses to strategically kill various bacteria that might be antibiotic resistant.
Viruses: Directors of Their Own Fate?
In the wake of the recent deadly avian flu virus, critics have questioned whether the spreading from mammal to mammal could have occurred on its own. A study completed at MSU by Justin Meyer was started with the thought that it would be a wild goose chase. Meyer wondered if lambda phages could evolve another way a new way to enter its host.
lambda was used to infect the gut bacterium E. coli. It is harmless to humans. The most common means for lambda to get into a cell is by attaching to its outer membrane. The genes and proteins contained by the lambda are then injected into the microbe. Meyer used E. coli that didn’t make the molecules necessary for the virus to grab onto. This meant that the only viruses that would survive were ones that mutated to use a different surface molecule. Shockingly, within 15 days, Meyer’s experiment showed that viruses were using a new channel in E. coli known as OmpF.
Meyer re-conducted the experiment with 96 lines of the virus and E. coli. Of those 96, 24 of the lines began to use OmpF as the pathway into the host. Because of the repeating phenomenon, the genomes of the evolved viruses were sequenced, finding that four mutations were required for the viruses to thrive. All four were required, not a single one, or even three out of the four. Meyer estimated the chance of all four mutations arising at once was nearly impossible: one in a thousand, trillion, trillion. However, the lambda viruses evolved to contain all four mutations in a couple weeks on a regular basis.
As incredible as this experiment is, it is somewhat frightening. Meyer showed how easily viruses can evolve completely new traits, which can lead to new diseases. This is exactly the reason why when treating a sickness with antibiotics, the patient MUST finish taking the dosage until it is gone, otherwise the virus can come back even stronger.