Temperature-dependent reprogramming of virulence traits during Pseudomonas aeruginosa biofilm formation

Abstract

Pseudomonas aeruginosa is an opportunistic pathogen that occupies diverse ecological niches, including soil, water, and the human host. Environmental cues encountered across these habitats trigger adaptive responses that promote survival and persistence through regulation of virulence-associated traits, including secreted factors, siderophores, and biofilm exopolysaccharides (EPS). One major change experienced during the transition from environmental reservoirs to the host is an increase in temperature. Although temperature is a key signal encountered during host transition, its global impact on P. aeruginosa physiology remains poorly understood. We therefore investigated the effects of temperature on planktonic and biofilm-populations, comparing both growth states at 23°C and 30°C, representing environmental temperatures, and at 37°C and 40°C, representing normal and febrile host temperatures. Transcriptomic and phenotypic analyses revealed extensive temperature-dependent regulation of virulence determinants in both growth states. Expression of the type VI secretion system was elevated at environmental temperatures, whereas pyoverdine biosynthesis and the type III secretion system were upregulated at host temperatures. Building on our previous finding that biofilms formed at environmental and host temperatures differ in architecture, biomass, and EPS composition, we next examined how these structural differences influence stress tolerance. Biofilms grown at 23°C and 30°C exhibited substantially greater tolerance to antibiotic stress than biofilms grown at 37°C and 40°C. Growth temperature therefore establishes biofilm properties that subsequently influence the stress-tolerance profile of the population. Collectively, our findings identify temperature as a major environmental cue that reprograms P. aeruginosa physiology in ways likely to support persistence across distinct ecological niches. Importance Pseudomonas aeruginosa causes serious infections in individuals with cystic fibrosis, burn wounds, and compromised immune systems, but also persists in diverse environmental reservoirs. During transition from the environment to the host, this bacterium encounters a predictable increase in temperature that may regulate physiology and virulence. Because most laboratory studies are conducted at 37°C, the effects of environmentally relevant temperatures remain poorly understood. We examined gene expression and virulence-associated phenotypes across four temperatures in both planktonic and biofilm growth states. Temperature differentially regulated host-associated and environmental virulence programs, including elevated T3SS at host temperatures and T6SS at environmental temperatures. Notably, biofilms formed at environmental temperatures exhibited greater antibiotic tolerance. These findings reveal temperature as a powerful ecological cue directing environmental-to-host adaptation in P. aeruginosa.