Invasion of pseudomonas aeruginosa populations through the altered expression of pyoverdine primary and secondary receptors

Abstract

‘Evolutionary medicine’ has been proposed as an alternative treatment of infectious diseases in response to the emergence of multidrug resistant bacterial pathogens and to the limited availability of new antibiotics. Among potential treatments, microbial “Trojan horses” are a way of deploying weaknesses in microbial populations by invading them with tailor-made bacteria (e.g. sensitive to antibiotics). Here I exploit the fitness cost linked to the production of the siderophore pyoverdine in the human pathogen Pseudomonas aeruginosa for population invasion. Individuals in a population that do not produce the siderophore do not pay the cost and can overtake a population. However, cooperative individuals are preserved by the presence of structure in the population (e.g. growth in biofilms) that limits the diffusion of pyoverdine, therefore preventing the invasion by non-cooperators. I overcame this limitation by altering the individual benefit acquisition through the deletion and/or overexpression of pyoverdine primary (FpvA) and secondary receptors (FpvB). I characterised growth and pyoverdine production strategies in iron limited conditions in a variety of scenarios in both monocultures and competition experiments against the wildtype MPAO1. My results show that the selective manipulation of pyoverdine receptors leads to different evolutionary dynamics in the population, which are dependent on the relationship between costs of pyoverdine production and benefits of reception during balanced growth, as well as in the kinetics of this process prior to exponential growth. These strategies change in response to environmental inputs such as the presence of a stressor and are maintained when cells grow in biofilms and during infections of Galleria mellonella, both of which are representative of structured environments. By interfering with the complex regulatory network of pyoverdine production and reception, I produced strains with optimised investments under certain conditions that successfully displace a wildtype population therefore paving the way for their use as ‘Trojan horses’ for population control.