Multilocus Sequence Analysis of the Marine Bacterial Genus Tenacibaculum Suggests Parallel Evolution of Fish Pathogenicity and Endemic Colonization of Aquaculture Systems

Abstract

The genus Tenacibaculum, a member of the family Flavobacteriaceae, is an abundant component of marine bacterial ecosystems that also hosts several fish pathogens, some of which are of serious concern for marine aquaculture. Here, we applied multilocus sequence analysis (MLSA) to 114 representatives of most known species in the genus and of the worldwide diversity of the major fish pathogen Tenacibaculum maritimum. Recombination hampers precise phylogenetic reconstruction, but the data indicate intertwined environmental and pathogenic lineages, which suggests that pathogenicity evolved independently in several species. At lower phylogenetic levels recombination is also important, and the species T. maritimum constitutes a cohesive group of isolates. Importantly, the data reveal no trace of long-distance dissemination that could be linked to international fish movements. Instead, the high number of distinct genotypes suggests an endemic distribution of strains. The MLSA scheme and the data described in this study will help in monitoring Tenacibaculum infections in marine aquaculture; we show, for instance, that isolates from tenacibaculosis outbreaks in Norwegian salmon farms are related to T. dicentrarchi, a recently described species.

Genotyping of Tenacibaculum maritimum isolates from farmed Atlantic salmon in Western Canada

“…PCRs were performed on the T. maritimum isolates using primers designed by Habib et al. () for 11 HK genes. Amplifications were performed at 94°C for 5 min, 35 cycles of 94°C for 30 s, 55°C (50°C for primers: glyA , infB , tgt , tuf and yqfO ) for 30 s and 72°C for 1 min, followed by 72°C for 10 min using the same reaction mixture and machine as above.…”

“…The second HK gene sequence alignment included concatenated sequences of the Canadian strains found in this study (Table ), the Norwegian T. maritimum strain NLF‐15 isolated from lumpsuckers, Cyclopterus lumpus (L.) (Småge, Frisch, Brevik, Watanabe, & Nylund, ), the Chilean T. maritimum strain Ch‐2402 isolated from Atlantic salmon (Apablaza et al., ), as well as a single strain from each of the 47 T. maritimum STs (identified by their ST number) described in Habib et al. ().…”

“…Although a lot of genetic research has been completed on T. maritimum strains from European, Asian and Australian waters (Habib et al., ), nothing is known about the genetic profile of T. maritimum from Western Canada. This study provides this knowledge and adds to the genotyping of T. maritimum worldwide.…”

Genetic Diversity of Flavobacterium psychrophilum Isolates from Three Oncorhynchus spp. in the United States, as Revealed by Multilocus Sequence Typing

“…Multilocus sequence typing (MLST) is a robust, reproducible, and established technique to identify and characterize the strain diversity of human and animal bacterial pathogens (21, 22), including those affecting fish (23)(24)(25)(26)(27). MLST is based on the sequencing of, typically, 7 housekeeping gene loci, whereby an isolate is characterized by the allele types (ATs) found at the loci.…”

“…A number of molecular biology-based assays have been employed to study the genetic diversity of F. psychrophilum in an attempt to define its host specificity, geographical associations, and virulence (15-18). However, despite these concerted efforts, the lack of standardized, reproducible, and comparable assays (18)(19)(20) left the intraspecific heterogeneity of F. psychrophilum as it relates to distribution and transmission routes incompletely understood.Multilocus sequence typing (MLST) is a robust, reproducible, and established technique to identify and characterize the strain diversity of human and animal bacterial pathogens (21, 22), including those affecting fish (23)(24)(25)(26)(27). MLST is based on the sequencing of, typically, 7 housekeeping gene loci, whereby an isolate is characterized by the allele types (ATs) found at the loci.…”