Journal
DISEASES OF AQUATIC ORGANISMS
Volume 123, Issue 1, Pages 29-43Publisher
INTER-RESEARCH
DOI: 10.3354/dao03079
Keywords
Flagella; Gram-negative bacteria; fleQ; fliA; flaB; flaA; rpoN; Immunomodulatory; Legionella pneumophila
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Funding
- Comision Nacional de Investigacion Cientifica y Tecno logica de Chile (CONICYT) through grant FONDECYT [11130407]
- Fundacion COPEC-UC [2014.J.116]
- Fraunhofer Chile Research
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The Piscirickettsia salmonis genome was screened to evaluate potential flagellarelated 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 s28-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 en vironmental 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 in duced 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.
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