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Cooperative and harmful behaviour in the bacterial world
Publication . Domingues, Iolanda Lopes, 1986-; Dionísio, Francisco, 1971-; Lopes, Fátima
Bacteria are social organisms capable of displaying a multiplicity of complex behaviours, some of them with a significant impact on human lives. Antibiotic resistance, for one, is currently a major health menace and is typically envisioned as an asocial behaviour. Yet, sensitive bacteria can survive the action of antibiotics, given that their social entourage gathers the right characteristics. In this thesis social behaviour of bacteria, ranging from altruistic to spiteful, are shown to affect not only their survival, but also their ability to counterattack the invasion of competing bacteria, and ensure the preservation of social traits, such as antibiotic resistance. To ascertain the complexity and relevance of social behaviours on the bacterial world we studied two types of Escherichia coli mobile genetic elements: bacteriophages and plasmids. Such elements, are not only able to transmit horizontally between different bacterial lineages, but are also able to promote social behaviour in bacteria. In this thesis, both a temperate bacteriophage and three different conjugative plasmids were shown to act as promotors of bacterial social behaviours – both cooperative and harmful. Lysogenic bacteria were shown to use the λ bacteriophage as an allelopathic agent able to harm susceptible cells in their vicinity. This behaviour is of a spiteful nature towards the killed susceptible cells, but also proves to be altruistic towards surviving lysogenic bacteria in the population. Similarly, ampicillin-resistant bacteria, carrying conjugative plasmids, were able to cooperate in the detoxification of ampicillin enriched environments, which led to the survival of genetically sensitive bacteria. However, such sensitive hitchhikers did not remain unharmed for long. In fact, the resistant bacteria were able to use plasmids as a mechanism to harm plasmid-free bacteria and also to restore the cooperative antibiotic-resistance in the population. There is a great need to increase the general knowledge about bacterial social behaviours, since they are involved in well-known threats to public’s health. As far as bacteria are concerned, especially pathogenic bacteria, it is urgent to understand how social behaviours influence the ability of strains to survive the action of antibiotics, but also how they are able to cope when competing against non-pathogenic strains.
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Fundação para a Ciência e a Tecnologia
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SFRH
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SFRH/BD/82375/2011