Comparative Genome Analysis of Two Isolates of the Fish Pathogen Piscirickettsia salmonis from Different Hosts Reveals Major Differences in Virulence-Associated Secretion Systems

Bohle, H.; Henríquez, Patricio; Grothusen, Horst; Navas, Esteban; Sandoval, Álvaro; Bustamante, Fernando; Bustos, Patricio; Mancilla, Marcos

doi:10.1128/genomea.01219-14

Cited by 35 publications

(36 citation statements)

References 19 publications

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“…A previous study using drafted genomes suggested that P. salmonis PM15972A1 lacks one of the T4SS loci detected in the LF-89 strain (Bohle et al, 2014). We confirmed this fact in a T346Hunter analysis using the closed version of the sequence.…”

Section: Resultssupporting

confidence: 84%

The mutagenesis of a type IV secretion system locus of Piscirickettsia salmonis leads to the attenuation of the pathogen in Atlantic salmon, Salmo salar

Mancilla¹,

Saavedra²,

Grandón³

et al. 2017

Journal of Fish Diseases

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Piscirickettsiosis is a threatening infectious disease for the salmon industry, due to it being responsible for significant economic losses. The control of outbreaks also poses considerable environmental challenges. Despite Piscirickettsia salmonis having been discovered as the aetiological agent of the disease more than 25 years ago, its pathogenicity remains poorly understood. Among virulence factors identified so far, type four secretion systems (T4SS) seem to play a key role during the infection caused by the bacterium. We report here the genetic manipulation of P. salmonis by means of the transference of plasmid DNA in mating assays. An insertion cassette was engineered for targeting the icmB gene, which encodes a putative T4SS‐ATPase and is carried by one of the chromosomal T4SS clusters found within the genome of P. salmonis PM15972A1, a virulent representative of the EM‐90‐like strain. The molecular characterization of the resulting mutant strain demonstrated that the insertion interrupted the target gene. Further in vitro testing of the icmB mutant showed a dramatic drop in infectivity as tested in CHSE‐214 cells, which is in agreement with its attenuated behaviour observed in vivo. Altogether, our results demonstrate that, similar to other facultative intracellular pathogens, P. salmonis’ virulence relies on an intact T4SS.

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Section: Resultssupporting

confidence: 84%

The mutagenesis of a type IV secretion system locus of Piscirickettsia salmonis leads to the attenuation of the pathogen in Atlantic salmon, Salmo salar

Mancilla¹,

Saavedra²,

Grandón³

et al. 2017

Journal of Fish Diseases

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“…1). Moreover, we have demonstrated that all characterized P. salmonis strains have flagellar genes and share the same genetic organization (Eppinger et al 2013, Bohle et al 2014, Yañez et al 2014, Pulgar et al 2015. Our results suggest that P. salmonis has the potential to develop a flagellum controlled by this transcriptional cascade.…”

Section: Discussionmentioning

confidence: 58%

“…Once the genes were confirmed, the CLC Main Workbench 5 software (www.clcbio.com) was used to complement sequence analysis, specifically for accurate alignments, and to determine the putative operon organization of flagellar genes in P. salmonis. Finally, flagellar gene organization was compared between different P. salmonis strains using recently reported genomes (Eppinger et al 2013, Bohle et al 2014, Yañez et al 2014, Pulgar et al 2015.…”

Section: Screening Of the Piscirickettsia Salmonis Genomementioning

confidence: 99%

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

Carril

Gómez²,

Marshall³

2017

Dis. Aquat. Org.

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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 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.

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“…An understanding of the pathogenesis of SRS and of the biological mechanisms of the in vivo interaction of P. salmonis with its host would allow the development of alternatives for treatment, prevention and disease control. Although the sequences of the 16S rRNA gene and ITS 16S‐23S of several P. salmonis isolates show high similarity, strain EM‐90 isolated from Atlantic salmon farmed in Chile locates separately from LF‐89 isolates (Mauel et al., ), and it shows a different genetic pattern and a different number of secretion systems compared to strain LF‐89 (Bohle et al., ; Casanova et al., ). Despite the similarity between P. salmonis LF‐89 strains, differences in the virulence patterns of different isolates in i.p.…”

Section: Discussionmentioning

confidence: 99%

“…Isolate PS‐EM‐90 used in this study was obtained from a field outbreak described by Bohle et al. (), who reported that the main genomic differences between LF‐89 and EM‐90 are the number of secretion systems associated with virulence. This would explain the higher specificity of PS‐EM‐90 for Atlantic salmon.…”

Section: Discussionmentioning

confidence: 99%

Comparative pathogenesis of piscirickettsiosis in Atlantic salmon (Salmo salar L.) post‐smolt experimentally challenged with LF‐89‐like and EM‐90‐like Piscirickettsia salmonis isolates

Rozas‐Serri¹,

Ildefonso²,

Peña³

et al. 2017

Journal of Fish Diseases

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Piscirickettsiosis (SRS) is the most prevalent bacterial disease in Chilean salmon aquaculture and is responsible for high economic losses. The aim of this study was to comparatively characterize the pathogenesis of SRS in post-smolt Atlantic salmon during the early and late stages of infection with Piscirickettsia salmonis LF-89-like (PS-LF-89) and EM-90-like (PS-EM-90) using a cohabitation challenge. The pathogenesis of cohabitant fish infected with the two isolates was relatively different due to cohabitant fish infected with PS-EM-90 showing higher cumulative mortality and shorter time until death compared with PS-LF-89 fish. PS-LF-89 caused an SRS infection characterized by kidney and liver lesions, whereas PS-EM-90 caused systemic and haemorrhagic disease characterized by kidney, liver, heart, brain, skeletal muscle and intestine lesions. Decreased serum concentration of total proteins and albumin as well as increased serum ALT, AST and creatinine levels in fish infected with both isolates confirmed that changes in liver and kidney function occurred during infection. Tissue damage, expressed as an SRS histoscore, showed a strong positive correlation with the bacterial load expressed as abundance of P. salmonis 16S rRNA transcripts in the livers and kidneys of fish affected with either isolate, but the correlation was significantly higher in fish infected with PS-EM-90. The results contribute to improving the understanding of the bacteria-host interaction.

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Comparative Genome Analysis of Two Isolates of the Fish Pathogen Piscirickettsia salmonis from Different Hosts Reveals Major Differences in Virulence-Associated Secretion Systems

Cited by 35 publications

References 19 publications

The mutagenesis of a type IV secretion system locus of Piscirickettsia salmonis leads to the attenuation of the pathogen in Atlantic salmon, Salmo salar

The mutagenesis of a type IV secretion system locus of Piscirickettsia salmonis leads to the attenuation of the pathogen in Atlantic salmon, Salmo salar

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

Comparative pathogenesis of piscirickettsiosis in Atlantic salmon (Salmo salar L.) post‐smolt experimentally challenged with LF‐89‐like and EM‐90‐like Piscirickettsia salmonis isolates

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