Salinity and pH stress selection determine Ralstonia solanacearum plant pathogen adaptive trajectories via insertion sequence movement

Environmentally transmitted plant pathogens are often exposed to contrasting selection pressures within and between host environments during transmission. How selection in between-host environments affects pathogen evolution and diversification is, however, poorly understood. Here, we address this knowledge gap using the phytopathogenic Ralstonia solanacearum bacterium, which causes bacterial wilt disease and commonly persists in fresh water and soil environments when transmitting between host plants.To experimentally test if these environmental variables could cause diversification in R. solanacearum populations, an evolution experiment was conducted where genetically homogenous R. solanacearum isolate was exposed to acidic, alkaline or salinity stresses in single or in double combinations in vitro. Single stress selection resulted in specialist tolerance adaptations towards acidic or alkaline stress. While no adaptation to salinity was observed, the salt stress prevented R. solanacearum adaptation to acidic and alkaline conditions in double stress treatments. Overall, stress adaptations were costly in terms of reduced R. solanacearum metabolic capacity. Genome resequencing revealed only little genomic variation in terms of mutations and indels, stress adaptation was associated with insertion sequence (IS) movement in intergenic regions near genes encoding virulence and metabolic traits. Our findings suggest that environmental stress could drive R. solanacearum adaptive trajectories via IS movement, potentially affecting pathogen distribution and survival in environmental reservoirs during transmission between plant hosts. Here we provide the genome sequences of the evolved R. solanacearum isolates grown with pH and salinity stress.