DAO 123:29-43 (2017)  -  DOI: https://doi.org/10.3354/dao03079

Expression of flagellin and key regulatory flagellar genes in the non-motile bacterium Piscirickettsia salmonis 

Gabriela P. Carril1, Fernando A. Gómez1, Sergio H. Marshall1,2,3,*

1Laboratorio de Genética e Inmunología Molecular, Instituto de Biología, Facultad de Ciencias, Pontificia Universidad Católica de Valparaíso, Valparaíso 2340000, Chile
2Núcleo de Biotecnología Curauma, Pontificia Universidad Católica de Valparaíso, Valparaíso 2340000, Chile
3Fraunhofer Chile Research, Foundation on System Biotechnology, Santiago 7550296, Chile
*Corresponding author:

ABSTRACT: The Piscirickettsia salmonis genome was screened to evaluate potential flagella-related open reading frames, as well as their genomic organization and eventual expression. A complete and organized set of flagellar genes was found for P. salmonis, although no structural flagellum has ever been reported for this bacterium. To gain further understanding, the hierarchical flagellar cascade described for Legionella pneumophila was used as a reference model for putative analysis in P. salmonis. Specifically, 5 of the most relevant genes from this cascade were chosen, including 3 regulatory genes (fleQ, triggers the cascade; fliA, regulates the σ28-coding gene; and rpoN, an RNA polymerase-dependent gene) and 2 terminal structural genes (flaA and flaB, flagellin and a flagellin-like protein, respectively). Kinetic experiments evaluated gene expressions over time, with P. salmonis assessed in 2 liquid, cell-free media and during infection of the SHK-1 fish cell line. Under all conditions, the 5 target genes were primarily expressed during early growth/infection and were differentially expressed when bacteria encountered environmental stress (i.e. a high-salt concentration). Intriguingly, the flagellin monomer was fully expressed under all growth conditions and was located near the bacterial membrane. While no structural flagellum was detected under any condition, the recombinant flagellin monomer induced a proinflammatory response in SHK-1 cells, suggesting a possible immunomodulatory function. The potential implications of these observations are discussed in the context of P. salmonis biology and pathogenic potential.


KEY WORDS: Flagella · Gram-negative bacteria · fleQ · fliA · flaB · flaA · rpoN · Immunomodulatory · Legionella pneumophila


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Cite this article as: Carril GP, Gómez FA, Marshall SH (2017) Expression of flagellin and key regulatory flagellar genes in the non-motile bacterium Piscirickettsia salmonis . Dis Aquat Org 123:29-43. https://doi.org/10.3354/dao03079

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