Pseudomonas aeruginosa response to environmental cues: Insights into physiological adaptations in biofilms and potential therapeutic targets

Pseudomonas aeruginosa is an opportunistic pathogen known for its ability to adapt to extreme environmental conditions by forming surface-attached biofilms. A biofilm is a group of microbial cells embedded in a self-produced extracellular polymeric substances (EPS) matrix. The EPS forms the major component of the biofilm biomass and can provide both structural and functional properties to the biofilm, including protection from antimicrobial agents and immune attack during infections. In this study, we described Pseudomonas aeruginosa PA14 response to two main environmental cues, temperature, and carbon source availability. Using phenotypic screening, transcriptomics, proteomics, and microscopy tools we were able to show how this pathogen responds to temperature fluctuations, as temperature shift is a major component of its lifestyle from environment into the mammalian host. We selected 23˚C and 30˚C to mimic external environmental conditions and 37˚C and 40˚C to mimic the human host conditions. The temperature studies revealed many unique temperature-driven biofilm adaptations. First, we observed induction of an endogenous filamentous phage at host-temperatures. This phage was shown to provide a benefit to P. aeruginosa by specifically strengthening biofilms formed at host temperatures and therefore represents a potential drug target. Next, we observed an overall shift in biofilm architecture in the temperature range tested. This shift results in greater biomass at lower temperatures but higher production of the classical EPS components at higher temperatures. These findings open doors for the potential discovery of as-yet-uncharacterized EPS components. Finally, we observed an overall temperature-driven shift in the production of several virulence factors including T3SS, T6SS, pyocyanin, and pyoverdine. These findings provide potential insight into the types of competitive interactions most crucial to P. aeruginosa survival in distinct environmental niches. Our exploration into the impact of carbon source on P. aeruginosa physiology focused on a comparison of malonate versus glycerol growth conditions using phenotypic assays, transcriptomics, and whole genome sequencing (WGS). In this study, we expanded on the previous findings which report the role of malonate utilization on quorum sensing, virulence factor production, and formation of biofilm-like structures in P. aeruginosa. We identify that malonate as a carbon source can induce a global stress response and can activate glyoxylate and methyl citrate cycles. We also observed the intracellular accumulation of several metal ions, consistent with the observation that malonate utilization induces a metal stress response. We compared the responses of PA14 to those of other laboratory strains (PAO1 and PAK) as well as several cystic fibrosis isolates. Certain responses were conserved whereas others were unique to particular strains, indicating a high level of strain-specific adaptation to carbon sources. WGS studies provide some insight into the genetic source of these adaptations. Overall, we used diverse approaches in our study to investigate the link between environment fluctuations and pathogen adaptation response. The broader understanding of such dynamics can eventually contribute towards developing new and potential therapeutic targets for biofilm-associated infections in the future.

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