title: Pseudomonas fluorescens: fur is required for multiple biological properties associated with pathogenesis.
abstract: Pseudomonas fluorescens, a Gram-negative bacterium, is an aquaculture pathogen with a broad host range. In a previous study, we had demonstrated that knockout of the fur gene of a pathogenic P. fluorescens strain, TSS, resulted in profound virulence attenuation. In this work, we studied the properties of the fur knockout mutant, TFM, in comparison with the wild type strain TSS. We found that compared to TSS, TFM (i) was impaired in siderophore production and extracellular enzyme activities, (ii) exhibited altered global polarity, (iii) was dramatically reduced in the ability to resist oxidative stress, (iv) showed higher tolerance to manganese, and (v) exhibited significantly reduced cytotoxicity. When incubated with cultured host cells, TFM displayed a cellular binding index much lower than that of TSS. Neither TFM nor TSS was able to survive and replicate in host cells. Following inoculation into Japanese flounder (Paralichthys olivaceus), TSS upregulated the expression of a wide range of genes involved in innate immunity, notably IL-1β and two CC chemokines. In contrast, TFM caused significant inductions of only a few genes and to much lower magnitudes than TSS. Given the strong inductions of IL-1β and the two chemokines by TSS, the effect of these three genes on P. fluorescens invasion was examined. The results showed that overexpression of these genes in flounder significantly inhibited TSS dissemination into and colonization of host tissues. Taken together, these results indicate that Fur is required for multiple processes associated with virulence, and that proinflammatory cytokines and chemokines likely play important roles in the clearance of P. fluorescens infection.
authors.affiliation: Key Laboratory of Experimental Marine Biology, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China; University of Chinese Academy of Sciences, Beijing 100049, China.
authors.forename: Ze-jun
authors.initials: ZJ
authors.lastname: Zhou
authors.affiliation: Key Laboratory of Experimental Marine Biology, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China; University of Chinese Academy of Sciences, Beijing 100049, China.
authors.forename: Lu
authors.initials: L
authors.lastname: Zhang
authors.affiliation: Key Laboratory of Experimental Marine Biology, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China. Electronic address: lsun@qdio.ac.cn.
authors.forename: Li
authors.initials: L
authors.lastname: Sun
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D002470:Cell Survival; D002478:Cells, Cultured; D005393:Fish Diseases / Q000276:immunology* / Q000382:microbiology; D005432:Flounder / Q000382:microbiology*; D005786:Gene Expression Regulation; D055786:Gene Knockout Techniques / Q000662:veterinary; D006861:Hydrogen Peroxide / Q000494:pharmacology; D008345:Manganese / Q000494:pharmacology; D009154:Mutation; D018384:Oxidative Stress; D011551:Pseudomonas fluorescens / Q000201:enzymology / Q000235:genetics / Q000472:pathogenicity*; D012097:Repressor Proteins / Q000235:genetics* / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000662:veterinary; D017262:Siderophores / Q000378:metabolism; D014774:Virulence
chemical_list: D001426:Bacterial Proteins; D012097:Repressor Proteins; D017262:Siderophores; C068477:ferric uptake regulating proteins, bacterial; D008345:Manganese; D006861:Hydrogen Peroxide
keywords: Ferric uptake regulator; Immune gene expression; Infection; Pseudomonas fluorescens; Virulence