Pseudomonas fluorescens: fur is required for multiple biological properties associated with pathogenesis

Area of Science:

• Microbiology
• Aquaculture
• Bacterial Pathogenesis

Background:

• Pseudomonas fluorescens is a Gram-negative bacterial pathogen affecting aquaculture species.
• The fur gene is known to regulate virulence in many bacterial pathogens.
• Previous work showed fur gene knockout attenuates P. fluorescens virulence.

Purpose of the Study:

• To characterize the virulence properties of a fur knockout mutant (TFM) compared to the wild-type strain (TSS) of P. fluorescens.
• To investigate the role of Fur in P. fluorescens pathogenesis and host immune response.

Main Methods:

• Comparative analysis of wild-type (TSS) and fur knockout (TFM) P. fluorescens strains.
• Assessment of siderophore production, enzyme activities, oxidative stress resistance, and cytotoxicity.
• In vitro studies with cultured host cells and in vivo studies with Japanese flounder (Paralichthys olivaceus).
• Gene expression analysis of host innate immunity genes (IL-1β, CC chemokines).

Main Results:

• The TFM mutant showed impaired siderophore production, reduced extracellular enzyme activities, and lower resistance to oxidative stress compared to TSS.
• TFM exhibited significantly reduced cytotoxicity and lower binding to host cells.
• In Japanese flounder, TSS induced strong upregulation of innate immunity genes (IL-1β, CC chemokines), while TFM induced only minor changes.
• Overexpression of IL-1β and CC chemokines in flounder inhibited TSS dissemination and colonization.

Conclusions:

• The Fur protein is essential for multiple virulence-associated processes in P. fluorescens.
• Proinflammatory cytokines and chemokines play a significant role in clearing P. fluorescens infections.
• Targeting Fur or host immune responses could be potential strategies for controlling P. fluorescens infections in aquaculture.