Genomic characterization of newly isolated wide-host-range phages of Aeromonas salmonicida

Aeromonas salmonicida is a major fish pathogen and the causative agent of furunculosis that causes significant economic losses in the aquaculture industry worldwide. Possible alternative to antibiotic treatment of this disease could be phage therapy. Nine A. salmonicida phages were isolated from waste water plants in various cities in the Czech Republic. Four of them were studied more closely. Genomes of new lytic phages MBSA3, MBSA4, MBSA7 and MBSA9 were sequenced and analyzed by bioinformatics tools. Their morphology was determined by electron microscopy and their host spectrum was determined by spot lysis assay on bacterial strains originating from Czech fish farms. According to electron microscopy, all four phages belong to the family Myoviridae, but the phage MBAS9 differed in morphology. More than half of 30 tested bacterial strains were sensitive at least to one of the phages. Phages MBAS3, MBAS4 and MBAS7 differed in host spectrum although their genomes are very similar. The unit genome of these phages is approximately 170 kbp, which differs from the unit genome of phage MBAS9 (approximately 47 kbp) containing a different type of genome termini, which suggests a different packaging mechanism. In contrast to other phages, MBAS9 has unique sequence with low similarity to phages in genome databases. All newly characterized phages have wide host spectrum and they are suitable candidates for phage therapy of fish infections. We kindly acknowledge the financial support of the project: CZ.01.1.02/0.0/0.0/16_084/0009987