title: The genetic basis of Escherichia coli pathoadaptation to macrophages.
abstract: Antagonistic interactions are likely important driving forces of the evolutionary process underlying bacterial genome complexity and diversity. We hypothesized that the ability of evolved bacteria to escape specific components of host innate immunity, such as phagocytosis and killing by macrophages (MΦ), is a critical trait relevant in the acquisition of bacterial virulence. Here, we used a combination of experimental evolution, phenotypic characterization, genome sequencing and mathematical modeling to address how fast, and through how many adaptive steps, a commensal Escherichia coli (E. coli) acquire this virulence trait. We show that when maintained in vitro under the selective pressure of host MΦ commensal E. coli can evolve, in less than 500 generations, virulent clones that escape phagocytosis and MΦ killing in vitro, while increasing their pathogenicity in vivo, as assessed in mice. This pathoadaptive process is driven by a mechanism involving the insertion of a single transposable element into the promoter region of the E. coli yrfF gene. Moreover, transposition of the IS186 element into the promoter of Lon gene, encoding an ATP-dependent serine protease, is likely to accelerate this pathoadaptive process. Competition between clones carrying distinct beneficial mutations dominates the dynamics of the pathoadaptive process, as suggested from a mathematical model, which reproduces the observed experimental dynamics of E. coli evolution towards virulence. In conclusion, we reveal a molecular mechanism explaining how a specific component of host innate immunity can modulate microbial evolution towards pathogenicity.
authors.affiliation: Instituto Gulbenkian de Ciência, Oeiras, Portugal.
authors.forename: Migla
authors.initials: M
authors.lastname: Miskinyte
authors.affiliation: Instituto Gulbenkian de Ciência, Oeiras, Portugal.
authors.forename: Ana
authors.initials: A
authors.lastname: Sousa
authors.affiliation: Instituto Gulbenkian de Ciência, Oeiras, Portugal.
authors.forename: Ricardo S
authors.initials: RS
authors.lastname: Ramiro
authors.affiliation: Instituto Gulbenkian de Ciência, Oeiras, Portugal.
authors.forename: Jorge A Moura
authors.initials: JA
authors.lastname: de Sousa
authors.affiliation: Instituto Gulbenkian de Ciência, Oeiras, Portugal.
authors.forename: Jerzy
authors.initials: J
authors.lastname: Kotlinowski
authors.affiliation: Instituto Gulbenkian de Ciência, Oeiras, Portugal ; Unidade de Imunologia Clínica, Instituto de Medicina Molecular, Faculdade de Medicina da Universidade de Lisboa, Lisboa, Portugal.
authors.forename: Iris
authors.initials: I
authors.lastname: Caramalho
authors.affiliation: Centro Biologia Ambiental, Faculdade de Ciências da Universidade de Lisboa, Lisboa, Portugal.
authors.forename: Sara
authors.initials: S
authors.lastname: Magalhães
authors.affiliation: Instituto Gulbenkian de Ciência, Oeiras, Portugal.
authors.forename: Miguel P
authors.initials: MP
authors.lastname: Soares
authors.affiliation: Instituto Gulbenkian de Ciência, Oeiras, Portugal.
authors.forename: Isabel
authors.initials: I
authors.lastname: Gordo
mesh_terms: D000220:Adaptation, Biological / Q000235:genetics*; D000818:Animals; D002478:Cells, Cultured; D004926:Escherichia coli / Q000235:genetics* / Q000472:pathogenicity*; D056084:Genetic Fitness; D014644:Genetic Variation; D015658:HIV Infections / Q000235:genetics / Q000821:virology; D057131:Immune Evasion / Q000235:genetics; D007113:Immunity, Innate; D008264:Macrophages / Q000276:immunology / Q000382:microbiology*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D010641:Phenotype; D014774:Virulence / Q000235:genetics