Genomic diversity of bacteriophages infecting the fish pathogenFlavobacterium psychrophilum

Abstract

Bacteriophages infecting the fish pathogen Flavobacterium psychrophilum can potentially be used to prevent and control outbreaks of this bacterium in salmonid aquaculture. However, the application of bacteriophages in disease control requires detailed knowledge on their genetic composition. To explore the diversity of F. pyschrophilum bacteriophages, we have analyzed the complete genome sequences of 17 phages isolated from two distant geographic areas (Denmark and Chile), including the previously characterized temperate bacteriophage 6H. Phage genome size ranged from 39 302 to 89 010 bp with a G+C content of 27%-32%. None of the bacteriophages isolated in Denmark contained genes associated with lysogeny, whereas the Chilean isolates were all putative temperate phages and similar to bacteriophage 6H. Comparative genome analysis showed that phages grouped in three different genetic clusters based on genetic composition and gene content, indicating a limited genetic diversity of F. psychrophilum-specific bacteriophages. However, amino acid sequence dissimilarity (25%) was found in putative structural proteins, which could be related to the host specificity determinants. This study represents the first analysis of genomic diversity and composition among bacteriophages infecting the fish pathogen F. psychrophilum and discusses the implications for the application of phages in disease control.

Prevalence of genetically similarFlavobacterium columnarephages across aquaculture environments reveals a strong potential for pathogen control

“…In addition, the isolated phage genomes were highly similar to the previously described phages in our dataset, as also reported earlier with phages infecting the genetic group C bacteria (Laanto et al, 2017). Comparable findings have been reported also in other phage-bacterium systems, for example with aquaculture pathogens F. psychrophilum and Vibrio anquillarum (Castillo and Middelboe, 2016;Kalatzis et al, 2017), where genetically similar phages were widely distributed across large temporal and spatial scales. Phages infecting flavobacterial species are known to regulate the genetic and phenotypic diversity of their bacterial hosts.…”

Diversity and Host Interactions among Virulent and Temperate Baltic Sea Flavobacterium Phages

“…Still, there was low similarity to any specific phage, which was confirmed by VICTOR analysis (Figure 3). The closest relationship to a previously known phage was a distant connection between tant8-1 and Flavobacterium phage Fpv5 (Figure 3), a similar-sized (42.6 kb) siphovirus isolated from fish farms in Denmark [46,48]. This points towards a shared ancestor of this viral type among phages infecting various Flavobacterium hosts in the Baltic Sea region.…”

“…Further, no genes involved in lysogenic replication were detected, indicating that mumin-, pippi-, and tantphages are only capable of lytic replication. This is also true for Flavobacterium phage Fpv5, which is related to tant8-1, where no genes that would indicate a possible lysogenic lifestyle were detected [48].…”

“…The Cellulophaga phages have proved to be an important model system for investigations of phage-host interactions, ranging from host range variations to transcriptomic analyses [4,8,10,[41][42][43]. Bacteroidetes phages have also shown their potential as bio-control agents in aquatic environments [44,45], and a large diversity of both virulent and temperate phages infecting Flavobacterium psychrophilum have been isolated from fish farms [46][47][48]. As F. psychrophilum is a fish pathogen that causes large economic losses [49], the potential of using phage therapy to control this disease is of great importance.…”

“…As F. psychrophilum is a fish pathogen that causes large economic losses [49], the potential of using phage therapy to control this disease is of great importance. Overall, these comprehensive phage collections constitute an ideal model system for both the investigation of genetic diversity and phage-host interactions [48,50,51].…”