EVOGENE/CIME Extra Seminar - Extrachromosomal genetic elements in Piscirickettsia salmonis: How genomic sequencing reveals new insights in bacterial evolution and environmental interactions

Piscirickettisa salmonis is a facultative intracellular pathogen that affects farmed salmonids around the world, and causes major loss in the Chilean aquaculture industry. This Gram-negative fastidious bacteria produces a systemic infection characterized by colonization of several organs in the fish. P. salmonis is able to infect, survive, and replicate inside salmonid macrophages, however little is known about its mechanisms of pathogenesis. This bacterium was originally isolated in diseased coho salmon in South Chile, but numerous strains have been discovered ever since. Recent sequencing efforts accomplished to close the genome of the reference strain LF-89 ATCC VR-1361. Sequencing the bacteria shed light in the genomic potential for colonizing and infecting the host, but also in the environment and interactions the bacteria stablishes. The bacterial genome contains one circular chromosome of 3.2 Mb and four plasmids: pPSLF89-1 (180 kb), pPSLF89-2 (33 kb), pPSLF89-3 (51 kb) and pPSLF89-4 (57 kb).Using bioinformatics tools we were able to find several putative virulence factor genes encoded both in the chromosome and in the plasmids. Among these were defense mechanisms, numerous prophages and mobilome related genes. These results suggest an ongoing exchange of information between this intracellular pathogen and its environment.