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Ecology and evolution of bacteriophages

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Resumo:Viruses that infect bacteria (phages) can directly drive host death required for their multiplication or alternatively remain in a dormant state (prophage) inside the host, being vertically transmitted to host offspring. Due to host exploitation, phages are usually seen as parasites. However, as a symbiont, the virus can confer some advantages to the host, such as immunity to further infections caused by related virus. Some authors proposed that lysogens (hosts harbouring prophages) can use their pathogens to harm susceptible conspecifics. This behaviour, in which the actor (lysogenic individual) experiences a cost (death) to cause damage to conspecifics is called spite. In a further extent this behaviour can be seen as indirect altruism, because the actor by displacing competitors allows its relatives to have access to more resources, thus benefiting them. Here we show that when competing with susceptible conspecifics in unstructured habitats, there is an optimum initial frequency of lysogens leading to benefit. Above this optimum, the cost of phage production is higher than the benefit associated to the displacement of susceptibles, while under the optimum frequency the viral production is not sufficient to efficiently outcompete susceptibles. However, when competing in structured habitats, spiteful advantage is always seen at short term. At long term, conversion of susceptibles into lysogens predominates. After conversion, the frequency of lysogens decreases if initially rare, or maintains at a certain level if initially common. We also show that after evolution in conditions, phages become more virulent while bacteria become resistant to the phage. Thus, the evolved strain becomes more competitive. In conclusion, we that indeed there is spiteful behaviour at short term. However, the effect of spite in often cancelled because susceptible individuals became phage-immune by lysogenization.
Autores principais:Gama, João Pedro Alves da, 1988
Assunto:Bacteriófagos Competição Imunidade Teses de mestrado - 2011
Ano:2011
País:Portugal
Tipo de documento:dissertação de mestrado
Tipo de acesso:acesso aberto
Instituição associada:Universidade de Lisboa
Idioma:inglês
Origem:Repositório da Universidade de Lisboa

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