THE BLOG

Bacteriophage: The Microscopic Black Market

14/12/2015 10:18 GMT | Updated 13/12/2016 10:12 GMT

As we learn more about bacteria, it is becoming ever clearer that they interact with themselves and the environment with more sophistication than we ever dared to imagine. Of course understanding as much as possible about bacteria's day to day life is very important, as it comes with countless implications for how we understand and treat disease.

It was once thought that bacteria only live to nourish themselves and divide, passing their genes on to their daughter cells. However, this model failed to explain the incredibly fast adaptability that bacteria seem to demonstrate when they're exposed to harsh conditions. They are survival machines, and by working together as a population to spread positive genes for survival quickly and efficiently, they are slowly managing to overcome some of the best medical treatments we have ever created.

There are several different ways that bacteria achieve this gene transfer; from taking in the genes of dead bacteria to see if they left behind anything useful, to 'getting it on' with their fellow living bacteria and exchanging DNA. However, if you thought that this was the most fascinating aspect of bacterial life, then you were wrong; it gets even better.

As a society we're taught to think, mostly by the cleaning industry and the media, that all bacteria and viruses are evil beings to be feared. They're on the same side, they've formed a coalition, and now they're out to get us. But it may surprise you to hear, that just like with humans, bacteria are also susceptible to infection by viruses. These viruses are called bacteriophage, but also just like humans, not all of these viruses are necessarily harmful.

Certain bacteriophage, like the Stx phage studied by scientists at the University of Liverpool, inadvertently act as DNA Parcel Force for bacterial populations. This happens by a convenient mistake of nature, where a virus will infect a bacterial cell, but instead of packaging up its own replicated DNA and moving off to infect more cells like it is designed to, it accidentally picks up a bit of bacterial DNA. Sometimes these fragments of bacterial DNA encode useful genes, so when the bacteriophage infects another bacterium, it inserts the useful DNA from its last victim into the next, and this DNA may become temporarily stable within the bacterium (something called a lysogenic cycle). This useful DNA is now available for the newly infected bacterium to use to increase its chances of survival.

Data from researchers at the University of Liverpool, looked at the effects of an Stx phage gene on the pathogenic strain of E. coli called 0157:H7 (don't worry, I won't test you on the name). We do have plenty of 'friendly' E. coli in our bodies, but when this strain of E. coli is ingested, it can colonise susceptible areas of our digestive tract and cause disease. What's so significant about this study, is that these researchers have gone against the standard dogma and have been able to identify a single gene that has originated from the Stx phage transfer, that controls the bacterium's ability to survive acidic conditions. Why is that important? Well, if it wasn't for acid resistance, the E. coli would be killed by the stomach acid before it colonised the gut and caused disease.

This is evidence of a virus actually controlling a bacterium's ability cause human disease. Like all good science, this sort of black-market gene trade between bacteria raises a lot more questions than it answers. In a world where humans and bacteria are locked in a constant struggle for control over one another, these sort of answers could be essential to making sure that we come out on top.