Sex and Death in bacteria: Pawel Sierocinski explains!

Hi all, it has been a while since I last posted (I had a good excuse though, see previous post) and it is time to get this blogging thing going again! ECEHH Communications and Outreach manager Alex Smalley very recently conducted a video interview with Associate Research Fellow Pawel Sierocinski about his project ‘Sex and Death: testing the evolutionary benefit of recombination using a bacterium and bacteriophage model’. The video, along with a brief project description, can be found here. Pawel has also written a more extensive project description that I will paste below, enjoy!

During the course of my PhD project I contracted deep and lasting admiration for the process of evolution. The simplicity and elegance of it combined with complexity it can yield charmed me. I started to read about latest developments in evolutionary biology, started blogging about it. It was only natural that when opportunity of working on topics more directly linked with evolutionary biology would arrive, I will definitely take it. That was the moment I learned of Michiel’s idea of testing whether bacteria engage in ‘sex’ to be able to escape their parasites.

Bacteria are constantly attacked by viruses (termed bacteriophages or phages). Phages infect bacteria by introducing their genetic material into the cell and hijacking their replication machinery. This leads to the cell lysing, releasing the phage offspring. Such deadly infections exert great selective pressure on bacteria to produce novel resistant types and in turn for the phage to overcome this resistance. It has been shown previously that bacteria and phage can coevolve for many generations. It is of vital importance for the bacteria to generate variation in their populations. To achieve that, bacteria do not solely rely on mutations but also on the exchange of stretches of DNA. One important mechanism of horizontal gene transfer is transformation: the uptake of DNA from the environment followed by its recombination into the genome. This process can be compared to eukaryote sex: bacteria increase variation not based on mutation, but based on shuffling around existing genetic variation.

Perhaps the most prominent explanation for the benefits of eukaryote sex is the Red Queen Hypothesis. It is based on a quote from Lewis Carrol’s ”Through the Looking-Glass”: “It takes all the running you can do, to keep in the same place.”. It means that in highly competitive environments, majority of the effort is invested into keeping your niche, rather than expanding it. One month of experimental evolution in bacteria can easily span more than a 100 generations, so a similar experiment in humans would have to last over 2000 years. The ability to manipulate and evolve bacteria and phage in the lab make them a simple yet very powerful model system to test the Red Queen Hypothesis. Getting empirical proof of a system based on the Red Queen dynamics is an important finding in evolutionary biology. Moreover, such experiments may answer important questions not only related to evolutionary biology, but also to human wellbeing. It has been shown, that bacteria use transformation not only when being attacked by viruses, but also while attacking humans. Pathogens very often share genetic elements responsible virulence, or antibiotic resistance, with other pathogens. Understanding how does this process work, adds key insight to our understanding of the evolution of diseases.

Our plan is to combine evolution experiments with molecular biology to let us understand: Can bacteria use DNA of other bacteria to become resistant to their parasites? We will use the common aquatic pathogen Aeromonas. Those bacteria are pretty common in freshwaters and usually safe for humans. Sometimes, however, they can cause serious diseases. The infections with Aeromonas were the most common type of infection after the 2004 tsunami in Asia. Aeromonas species are also very common and dangerous pathogens of fish, including salmon. They will be grown together with bacteriophages able to infect them. We will test whether the rate of bacterial adaptation can be increased by the addition of DNA from strains that have before evolved resistance to the phages. I hope to get you updated on the project as it progresses, but might also update you on more general topics related with living and working in Cornwall or research of our other colleagues. Till then!

Pawel

P.S.

The project is partly funded by (inhale) investment from the European Regional Development Fund and the European Social Fund Convergence Programme for Cornwall and the Isles of Scilly to the ECEHH (exhale) and by a NERC New Investigator Grant (hurray!).

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