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Meet Dr Louise Johnson
In this video, Dr Louise Johnson and Professor Rob Jackson explain how bacteria evolve a replacement flagellum – a rotating tail-like structure.
In this Step, I’m in the Cole Museum of Zoology with Dr. Louise Johnson to discuss how she uses microbes in her research to study evolution in action. So Louise, could you give me a little idea about how we can actually use microbes to study evolution? Well, microbes are amazing for studying evolution, because you can study tens of thousands of generations if you want, which a particular famous experiment called the long-term evolution experiment has got up to about 70,000 generations now, which would be impossible to do with mice or bigger organisms of that kind. And that experiment has helped answer questions in evolutionary biology that people have been arguing about and debating sometime since Darwin.
Another really cool thing, though, is that you can keep them in the freezer. So if you have an ancestor, and you evolve a new ability or a improved ability to do something, you can directly compare your evolved strain with the ancestor from the freezer and quantify the improvement due to evolution. So you can make it all much more statistically sound. And you can apply selection in the lab essentially, like try and kill them, and watch evolution happen as they evade whatever you’re doing to them, or get better at using a food source, or whatever. And how do you actually study that, because bacteria are so small? And how do you actually see them mutating or becoming better at something?
Well, sometimes, it can be quite subtle. You might want to measure their growth rate by shining, essentially shining a light through a solution of them, and the more of them there are, the more of a shadow they cast. But in some cases, you can see when an evolutionary event has happened. And one example of this was a really fun project that I got involved with with Rob Jackson and various other collaborators here at Reading and elsewhere, where we were looking at the re-evolution of motility, of the ability of bacteria to use their flagellum to swim.
And in that case, we could see, very clearly on a dish, whether the bacterium had to stay in the middle, or if it could swim out over the whole of the dish and grow everywhere. And that was a lovely, clear example of evolution in action and happening very fast. The interesting thing, from my perspective, was about how repeatable it was. Sometimes, you saw the very same change to the very same gene causing this newfound ability to swim in these bacteria. And so very, very precisely, evolution was finding the right way to solve a problem, which is absolutely fascinating to me. And how are you actually able to study that mutation? What actually happens in a cell?
Well, for that, we needed our collaborators. We could use some really quite sophisticated molecular biology to find out exactly which genes had changed. Our biochemistry collaborators could say what they thought would happen inside the cell because of those changes to the genes. Our structural biology collaborators could say precisely what the mutation in the gene did to the protein. So each person was in charge of a different aspect of that project, which made it very exciting to be part of. One of those collaborators was Rob Jackson, who we actually met earlier in the course. So I’ve gone back to speak to Rob about his role in this study.
So Rob, I’ve just been speaking to Louise and she’s just told me that you’ve made this really, really interesting discovery on how bacteria is able to rewire its flagellum. Could you please explain to me a little bit about that? Yeah. So what we were able to do was to use DNA sequencing, so genome sequencing actually. So this is where we can read the bases of DNA within the whole genome. So the bacterium has a single chromosome. And that chromosome has about 6 million letters in it, so bases. And a series of those will make a gene to make a protein. And what we did was we went and read the whole genome, all 6 million letters of that bacterial genome.
And then we had to go and search and see if there were any changes in the mutant, the one that’s evolved, to make the flagellum versus the original one. And it was incredible. We found the needle in the haystack. 6 million, only one change was found to occur. And we found that change, and when we located what it was doing, we realised that it was essentially changing the way the bacterium behaves to reactivate its flagellum. OK. Thanks, Rob. It’s been great speaking to you. It’s been wonderful hearing about what you’ve been doing in your lab, and I really look forward to hearing what’s going to come out in the future.
You may be surprised to hear that many scientific discoveries have been made by chance. Our chance discovery was that we accidentally left experimental samples out for longer than needed and in doing so something remarkable happened.
In this video, I meet with Dr Louise Johnson and Professor Rob Jackson (who you met in Step 1.18) who explain how this meant that they found that a simple bacteria can restart their ‘outboard motor’ by hotwiring their own genes. Unable to move and facing starvation, the bacteria evolve a replacement flagellum – a rotating tail-like structure which acts like an outboard motor – by patching together a new genetic switch with borrowed parts.
Recommended reading
- After you watch the video, you can find out more about our research by reading our blog and paper on ScienceMag.
This article is from the online course:
Small and Mighty: Introduction to Microbiology
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Small and Mighty: Introduction to Microbiology
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