The c-di-GMP signalling component YfiR regulates multiple bacterial phenotypes and virulence in Pseudomonas plecoglossicida.

Abstract

Pseudomonas plecoglossicida (P. plecoglossicida) is the causative agent of visceral granulomas disease (VGD) in large yellow croaker (LYC, Larimichthys crocea) and it causes severe economic loss to its industry. Biofilm formation, related to intracellular cyclic di-GMP levels, is essential for the lifestyle of P. plecoglossicida. This research aims to investigate the role of YfiR-a key regulator of the diguanylate cyclase YfiN to regulate c-di-GMP levels and reveal its regulatory function of bacterial virulence expression in P. plecoglossicida. A genetic analysis was carried out to identify the yfiBNR operon for c-di-GMP regulation in P. plecoglossicida. Then we constructed a yfiR mutant and observed increased c-di-GMP levels, enhanced biofilm formation, increased exopolysaccharides, and diminished swimming and swarming motility in this strain. Moreover, through establishing a yolk sac microinjection infection model in zebrafish larvae, an attenuated phenotype of yfiR mutant that manifested as restored survival and lower bacterial colonization was found. YfiR is the key regulator of virulence in P. plecoglossicida, which contributes to c-di-GMP level, biofilm formation, exopolysaccharides production, swimming, swarming motility and bacterial colonization in zebrafish model.