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Open AccessArticle

Piscirickettsia salmonis Cryptic Plasmids: Source of Mobile DNA and Virulence Factors

1
Laboratorio de Bioinformática y Expresión Génica, Instituto de Nutrición y Tecnología de los Alimentos (INTA), Universidad de Chile, Santiago 7830490, Chile
2
Laboratorio de Microbiología de Sistemas, Departamento de Biología, Facultad de Ciencias, Universidad de Chile, Santiago 7800003, Chile
3
Centro de Modelamiento Matemático (AFB170001) and Departamento de Ingeniería Matemática, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile and UMI-CNRS 2807, Santiago 8370415, Chile
4
Fondap Center for Genome Regulation (Fondap 15090007), Universidad de Chile, Santiago 8370415, Chile
*
Author to whom correspondence should be addressed.
Pathogens 2019, 8(4), 269; https://doi.org/10.3390/pathogens8040269
Received: 16 October 2019 / Revised: 18 November 2019 / Accepted: 22 November 2019 / Published: 28 November 2019
(This article belongs to the Section Animal Pathogens)
Four large cryptic plasmids were identified in the salmon pathogen Piscirickettsia salmonis reference strain LF-89. These plasmids appeared highly novel, with less than 7% nucleotidic identity to the nr plasmid database. Plasmid copy number analysis revealed that they are harbored in chromosome equivalent ratios. In addition to plasmid-related genes (plasmidial autonomous replication, partitioning, maintenance, and mobilization genes), mobile genetic elements such as transposases, integrases, and prophage sequences were also identified in P. salmonis plasmids. However, bacterial lysis was not observed upon the induction of prophages. A total of twelve putative virulence factors (VFs) were identified, in addition to two global transcriptional regulators, the widely conserved CsrA protein and the regulator Crp/Fnr. Eleven of the putative VFs were overexpressed during infection in two salmon-derived cellular infection models, supporting their role as VFs. The ubiquity of these plasmids was also confirmed by sequence similarity in the genomes of other P. salmonis strains. The ontology of P. salmonis plasmids suggests a role in bacterial fitness and adaptation to the environment as they encode proteins related to mobilization, nutrient transport and utilization, and bacterial virulence. Further functional characterization of P. salmonis plasmids may improve our knowledge regarding virulence and mobile elements in this intracellular pathogen. View Full-Text
Keywords: fish pathogen; Piscirickettsia salmonis; plasmids; MGE; virulence factors; prophages; gene annotation fish pathogen; Piscirickettsia salmonis; plasmids; MGE; virulence factors; prophages; gene annotation
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Ortiz-Severín, J.; Travisany, D.; Maass, A.; P. Chávez, F.; Cambiazo, V. Piscirickettsia salmonis Cryptic Plasmids: Source of Mobile DNA and Virulence Factors. Pathogens 2019, 8, 269.

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