Giant Phage Viruses

Sometimes (and probably most often than not), the kind of answers we expect to arrive at for a question limits the range of answers we may arrive at. In other words, sometimes we tend to ignore or even not see certain answers because we simply did not expect to see them. The case at hand is the discovery of giant-phage viruses that exist in our mouths and until recently nobody knew about them. According to The Atlantic,1 Jill Banfield of the University of California, Berkeley, and her team have discovered that these mega viruses exist in our saliva and in our gut, and they are 10 times bigger than other phages previously known.

It is interesting that Banfield and her team have discovered these viruses by accident. They were studying the gut bacteria of people from Bangladesh who are exposed to toxic arsenic compounds because they live near arsenic-contaminated groundwater. They were interested to know if the bacteria provide any form of detoxification for the arsenic. It turned out that they don't. However, the team found huge amounts of unknown viral DNA in the DNA of the bacteria. This was a hint at the existence of new and very complex phages, since phages are viruses that attack bacteria. Later on they found these genetic material in bacteria from other parts of the world.

Traditionally, to get to a virus scientists have to grow them, and this is done by first filtering out any particles above a certain size. In other words, the traditional techniques assume that viruses have to be below a certain size, and then proceed to filter out anything that does not fit that assumption. As a result, these giant phages had not been observed previously. However, Banfield and her team utilized a different technique: they started with environmental samples and analyzed the DNA of everything within those samples to see what cames out. It was by using this technique that they were able to isolate these giant phages. While an average phage has something in the order of 50k of DNA letters, these phages have something like 500k, almost ten times as much.

Although these phages do not cause any known diseases in humans, their very complex DNA structure is a potential sign that they probably do play some role. Whatever they do, however, their functions are likely to be different from traditional viruses. For example, because of their big size, they don't easily fit inside a bacterium and therefore they cannot reproduce many copies of themselves in a bacterium before bursting it. Thus, they should be more selective and exercise more control over their host to ensure the proper copying of themselves. In that sense, they would have to act more like mammals whose strategy is to put a lot of energy in fewer offspring rather than less energy in numerous offspring. The team also found that these phages actually seem to have their own way of cutting the genes of their hosts. Even more fascinating, they seem to be able to program their hosts to attack other phages, in other words, they seem to be able to utilize the genetic machinery of their hosts to put out their competition.

These findings are fascinating not only in their own term, but also because they raise deeper questions about the meaning of life. At the very least, these discoveries show that the simple division of living vs. non-living seems to be inadequate when it comes to such boundary cases. 

~~ Moe Azadeh

1. https://www.theatlantic.com/science/archive/2020/02/oh-look-ton-giant-viruses-inside-your-mouth/606763/?utm_medium=offsite&utm_source=yahoo&utm_campaign=yahoo-non-hosted&yptr=yahoo