Behind the social lives of bacteria Bacteria cooperate in many different ways, and this cooperation can increase the virulence of infections. Researchers in the SESE project are developing a model system for looking at social behaviours in infection, as well as exploring the possibility of disrupting infection through social cheat bacteria, as Professor Ashleigh Griffin explains. The propensity to
cooperate has evolved in many species over time, from ants, to humans, to monkeys, as it has become apparent that it can have a positive effect on the fitness of another individual. Cooperative behaviour can also be observed in bacteria, says Ashleigh Griffin, Professor of Evolutionary Biology at the University of Oxford. “Previously I worked to show that bacterial cells affected the fitness of their neighbours through their actions, either positively or negatively. These behaviours are then expected to evolve as a result of these fitness effects on others,” she outlines. This idea has largely entered the scientific mainstream, now Professor Griffin is the Principal Investigator of the SESE project, in which she and her collaborators are looking at social behaviour in bacterial infections. “In this project we’re trying to develop a model system to look at how social behaviours evolve in infection,” she explains.
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Cooperative green colonies and selfish white colonies growing on an agar plate.
Social behaviour This primarily means how cells influence each other. One way in which bacteria do this is by releasing enzymes into the surrounding environment to extract nutrients. “In the case of bacteria, enzyme degradation has to happen outside the organism, as they don’t
have a gut. Bacteria must release enzymes into the environment,” outlines Professor Griffin. If a bacterial cell’s neighbour is doing the same thing then they both have the opportunity to benefit from each other’s behaviour, an example of the kind of cooperative behaviour that Professor Griffin is investigating with her postdoc, Dr Melanie Ghoul. “We have been able to understand these cooperative behaviours by growing cooperative and non-cooperative bacteria together in test-tubes and watching how they evolve over time,” she says. The aim here is to identify the different factors that affect the extent to which bacterial cells cooperate. Researchers typically take a number of different issues into consideration. “We can look at what happens if we mix them together with relatives or non-relatives for example, or if we mix them together very densely. We can make all kinds of different adjustments to the conditions in the flask and ask the question; what’s the effect on
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