title: High temperature and bacteriophages can indirectly select for bacterial pathogenicity in environmental reservoirs.
abstract: The coincidental evolution hypothesis predicts that traits connected to bacterial pathogenicity could be indirectly selected outside the host as a correlated response to abiotic environmental conditions or different biotic species interactions. To investigate this, an opportunistic bacterial pathogen, Serratia marcescens, was cultured in the absence and presence of the lytic bacteriophage PPV (Podoviridae) at 25°C and 37°C for four weeks (N = 5). At the end, we measured changes in bacterial phage-resistance and potential virulence traits, and determined the pathogenicity of all bacterial selection lines in the Parasemia plantaginis insect model in vivo. Selection at 37°C increased bacterial motility and pathogenicity but only in the absence of phages. Exposure to phages increased the phage-resistance of bacteria, and this was costly in terms of decreased maximum population size in the absence of phages. However, this small-magnitude growth cost was not greater with bacteria that had evolved in high temperature regime, and no trade-off was found between phage-resistance and growth rate. As a result, phages constrained the evolution of a temperature-mediated increase in bacterial pathogenicity presumably by preferably infecting the highly motile and virulent bacteria. In more general perspective, our results suggest that the traits connected to bacterial pathogenicity could be indirectly selected as a correlated response by abiotic and biotic factors in environmental reservoirs.
authors.affiliation: Centre of Excellence in Evolutionary Research, Department of Biological and Environmental Science, University of Jyväskylä, Jyväskylä, Finland. vifriman@jyu.fi
authors.forename: Ville-Petri
authors.initials: VP
authors.lastname: Friman
authors.forename: Teppo
authors.initials: T
authors.lastname: Hiltunen
authors.forename: Matti
authors.initials: M
authors.lastname: Jalasvuori
authors.forename: Carita
authors.initials: C
authors.lastname: Lindstedt
authors.forename: Elina
authors.initials: E
authors.lastname: Laanto
authors.forename: Anni-Maria
authors.initials: AM
authors.lastname: Örmälä
authors.forename: Jouni
authors.initials: J
authors.lastname: Laakso
authors.forename: Johanna
authors.initials: J
authors.lastname: Mappes
authors.forename: Jaana K H
authors.initials: JK
authors.lastname: Bamford
mesh_terms: D000818:Animals; D005075:Biological Evolution; D004197:Disease Reservoirs / Q000382:microbiology*; D004783:Environmental Microbiology; D054884:Host-Pathogen Interactions; D006358:Hot Temperature; D007814:Larva / Q000382:microbiology; D009036:Moths / Q000382:microbiology; D009068:Movement; D017902:Podoviridae / Q000502:physiology*; D012706:Serratia marcescens / Q000472:pathogenicity* / Q000821:virology*; D016019:Survival Analysis