Evolution in Action

Bacteria are masters at adapting to their environment, rearranging their genetic material or gaining new genes from their surroundings. This has allowed them to colonise pretty much every conceivable environment. From boiling hot geysers to that pink scum in your shower. Even us.

Did you know that the number of cells that make up our body are outnumbered 10 to 1 by the bacteria that live on and in us? The majority of bacteria are either harmless or pretty beneficial, but some of them have evolved to cause us serious harm. Around the world, one out of every four people that die are killed by a microorganism of some sort. That’s a staggering 14 million people every year.

And you know what? They just keep on evolving! That’s how we get antibiotic resistance and new diseases emerging. So what we are interested in finding out is, how do bacteria evolve to cause disease?

Bacteria have a number of really useful characteristics that make them ideal for studying evolution:

  • They multiply really rapidly so we can measure change in a short space of time
  • They can be stored frozen in a sort of suspended animation. This means we can freeze bacteria from every step of our experiments, building up a living ‘fossil’ record which can be regrown and analysed at any time.
  • Modern sequencing techniques have made it relatively cheap and easy to sequence whole bacterial genomes so we can unravel any genetic changes that occur during our experiments.

So as not to create some superhuman killing machine able to rampage around the world Contagion-style, we are studying the evolution of a bacterium that doesn’t infect humans and isn’t spread by the air. Instead, we are using Citrobacter rodentium which infects mice using the same ‘modus operandi’ as food poisoning strains of E. coli do in humans. They go in one end… and come out the other! And because mice like to eat poo (more technically known as coprophagia) they easily spread C. rodentium to each other. We allow C. rodentium to spread from mouse to mouse to mouse to mouse to… you get the picture, each time freezing bacteria that are shed in the poo.

Glowing mouse poo visualised with our fancy imaging equipment

Glowing mouse poo visualised with our fancy imaging equipment

We use a glowing strain of C. rodentium so that we can track exactly where the bacteria are within the mice without having to kill the animals. We then carry out competition experiments between the original C. rodentium strain and the ‘evolved’ poop isolates to see which strains have gained a competitive edge. We do this by growing the strains in the lab as well as getting them to infect caterpillars. This gives a first clue as to whether the evolved isolates are starting to change the way they outsmart the primitive part of our immune system.

Why is this important?

This work will give us a better understanding of how infectious bacteria adapt, and how they might evolve in people in the future. This is very important – in the fight against an everchanging foe, forewarned is forearmed!

This work is being supported by the wonderful donors to our SciFund crowdfunding campaign, the Maurice Wilkins Centre for Molecular Biodiscovery, the Maurice and Phyllis Paykel Trust, an Advice First AMP ‘Do your thing’ scholarship, and the Faculty of Medical and Health Sciences at the University of Auckland.