Construction Of An Attenuated Pseudomonas Fluorescens Strain And Evaluation Of Its Potential As A Cross-protective Vaccine

Ferric uptake regulator (Fur) is a global transcription regulator that is ubiquitousto Gram negative bacteria and regulates diverse biological processes, including ironuptake, cellular metabolism, stress response, and production of virulence determinants.As a result, for many pathogenic bacteria, Fur plays a crucial role in the course ofinfection and disease development. In this study, the fur gene was cloned from apathogenic Pseudomonas fluorescens strain, TSS, isolated from diseased Japaneseflounder cultured in a local farm. TSS Fur can partially complement the defectivephenotype of an Escherichia coli fur mutant. A TSS fur null mutant, TFM, wasconstructed. Compared to TSS, TFM exhibits reduced growth ability, aberrantproduction of outer membrane proteins, decreased resistance against host serumbactericidal activity, impaired ability to disseminate in host blood and tissues, anddrastic attenuation in overall bacterial virulence in a Japanese flounder infectionmodel. When used as a live vaccine administered via the injection, immersion, andoral routes, TFM affords high levels of protection upon Japanese flounder against notonly P. fluorescens infection but also Aeromonas hydrophila infection. Furthermore, aplasmid, pJAQ, was constructed, which expresses the coding element of the Vibrioharveyi antigen AgaV-DegQ. TFM harboring pJAQ can secret AgaV-DegQ into theextracellular milieu. Vaccination of Japanese flounder with live TFM/pJAQ elicitedstrong immunoprotection against both V. harveyi and A. hydrophila infections.