VIRUEVO · The role of protozoa and phage enemies as driving force for bacterial virulence

Bacterial virulence has been traditionally thought to co-evolve in reciprocal selection with its host organism. However, in nature pathogens are embedded within a web of interactions which could indirectly affect evolution of bacterial virulence. Recent findings suggest that protozoan predation could increase pathogen virulence because bacterial defensive adaptations can correlate positively with bacterial ability to harm hosts. Yet, protozoan predation could also decrease bacterial virulence if increased allocation to anti-predatory traits is traded off with pathogen virulence. Thus, different type of protozoa could select for different anti-predatory adaptations which have opposite consequences for the evolution of bacterial virulence. Selection by other enemies such as phages (parasitic viruses) or abiotic environment could also select for bacterial traits that have correlated effects on pathogen virulence. However, despite indirect evidence that evolutionary interactions with natural enemies can drive bacterial virulence evolution, the direct, experimental evidence is lacking. In this proposal I concentrate on how protozoa and phage enemies affect the evolution of a bacterium’s (Pseudomonas fluorescens) defensive and virulence traits in two- and multi-species study systems in different environmental conditions. I will first perform microcosm experiments where I expose bacteria to single or multiple enemies, and then determine evolutionary changes in bacterial traits and measure the virulence in invertebrate host. The main aim is to determine how different microbial enemies indirectly select for bacterial virulence, and how defence and virulence related traits are correlated. Importantly, I will learn to work with P. fluorescens-phage system and perfect my skills in virulence assays. The concept of proposal is novel, merges knowledge between two labs and will strengthen the status of Europe as leading region in the study of experimental evolution.