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

Abstract

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 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.

Commercial vaccines do not confer protection against two genetic strains ofPiscirickettsia salmonis, LF-89-like and EM-90-like, in Atlantic salmon

“…The reaction was stopped with 50 µL of 1 N sulfuric acid and read at 450 nm on a VERSAmax microplate reader (Molecular Device, California, USA). For the detection of spIg, 50 ng µL -1 of total protein extract from P. salmonis (Carril et al, 2017) were seeded per well in a Maxisorp plate (diluted in 100 µL of carbonate buffer) and incubated overnight at 4 ºC. After blocking with 1% BSA (200 µL per well), each fish serum sample was incubated in duplicate at a total Igs concentration of 50 ng µL -1 for 90 min at ºC.…”

Addressing viral and bacterial threats to salmon farming in Chile: historical contexts and perspectives for management and control

“…; Carril et al . ), and a relationship between biofilm formation and genes related to chemotaxis has been suggested (Albornoz et al . ).…”

Comparative evaluation of experimental challenge by intraperitoneal injection and cohabitation of Atlantic salmon (Salmo salar L) after vaccination against Piscirickettsia salmonis (EM90‐like)

“…Chilean salmon industry has been challenged by piscirickettsiosis for almost 30 years (Almendras & Fuentealba, ; Carril, Gómez, & Marshall, ; Mauel & Miller, ), and currently, the disease produces economic losses around USD 700 million yearly (Maisey, Montero, & Christodoulides, ). Piscirickettsiosis has also been identified as the main reason for the use of 322.7 tons of antibiotics in Chile in 2018, where 95.5% was intended to treat this disease (SERNAPESCA, ).…”