Exposure to Freeze-Thaw Conditions Increases Virulence of Pseudomonas aeruginosa to Drosophila melanogaster.

Groundwater contamination by pathogenic bacteria present in land-applied manure poses a threat to public health. In cold climate regions, surface soil layers experience repeated temperature fluctuations around the freezing point known as freeze-thaw (FT) cycles. With global climate change, annual soil FT cycles have increased, and this trend is expected to continue. It is therefore of interest to understand how FT cycles impact soil microbial communities. This study investigates the influence of FT cycles on the growth, culturability, biofilm formation, and virulence of the bacterial opportunistic pathogen Pseudomonas aeruginosa, a ubiquitous bacterium found in soil and water, responsible for infections in immunocompromised hosts. Our findings demonstrate that exposure to FT had no significant effect on growth or culturability of the bacteria. However, FT treatment significantly increased biofilm formation and delayed the onset of swimming motility, factors that are important for the pathogenicity of P. aeruginosa. An in vivo study using a chronic infection model revealed an increase in the virulence of P. aeruginosa after FT exposure. These results suggest that the impact of climate change on natural FT cycles may be affecting the ecology of soil-borne pathogens and host-pathogen interactions in unexpected ways.