Faculté de Médecine
INSERM U1001 -Laboratory of Evolutive and Medical Molecular Genetics
24, rue du Faubourg St Jacques Faculté Cochin 6e étage
Abstracts (first author)
Bacterial sex can enhance cooperation
Mobile genetic elements, such as plasmids, are the most prominent mechanism of bacterial sex and play a large role in bacterial adaptation. Plasmids move between bacteria by conjugation, an active, unidirectional horizontal transfer of genetic material from donor to recipient cells. Since conjugation is costly for donors and is primarily controlled by the plasmid itself, horizontal transfer is usually seen as parasitism of the bacterial hosts. However, chromosomal genes can also influence horizontal transfer. Transferring plasmids could benefit the donor host by generating a specific behavior in recipients. Using both modeling and experimental work we show that if cooperation genes are located on the plasmid, conjugation can benefit the host bacteria by facilitating the maintenance of cooperation. We modeled populations of donor and recipients and showed that horizontal transfer increases the selection for cooperation by increasing relatedness and the overall amount of public good secreted in the population. This effect in turn allows for the selection of transfer: when cooperation is needed, genes increasing donor and recipient abilities can be selected both on the plasmid and on the chromosome. Our results could explain the high frequency of genes related to cooperation that are located on plasmids. In addition to the models, we used a synthetic system with independent control of cooperation and conjugation to experimentally test their relationship in Escherichia coli. We introduced multiple fluorescent proteins into bacterial strains and were able to measure the frequency of different types of bacteria, plasmids, as well as transfer events, by flow cytometry. We show that plasmid transfer indeed increases the selection for cooperation. Based on our models and experiments, we can conclude that the role that bacterial sex plays in evolution is strongly linked to the presence of and interaction with cooperation via public good secretion.