Microbiome Profiling Reveals a Microbial Dysbiosis During a Natural Outbreak of Tenacibaculosis (Yellow Mouth) in Atlantic Salmon

Abstract

Tenacibaculosis remains a major health issue for a number of important aquaculture species globally. On the west coast of Canada, yellow mouth (YM) disease is responsible for significant economic loss to the Atlantic salmon industry. While Tenacibaculum maritimum is considered to be the primary agent of clinical YM, the impact of YM on the resident microbial community and their influence on the oral cavity is poorly understood. Using a 16s rRNA amplicon sequencing analysis, the present study demonstrates a significant dysbiosis and a reduction in diversity of the microbial community in the YM affected Atlantic salmon. The microbial community of YM affected fish was dominated by two amplicon sequence variants (ASVs) of T. maritimum, although other less abundant ASVs were also found. Interestingly clinically unaffected (healthy) and YM surviving fish also had a high relative abundance of T. maritimum, suggesting that the presence of T. maritimum is not solely responsible for YM. A statistically significant association was observed between the abundance of T. maritimum and increased abundance of Vibrio spp. within fish displaying clinical signs of YM. Findings from our study provide further evidence that YM is a complex multifactorial disease, characterized by a profound dysbiosis of the microbial community which is dominated by distinct ASVs of T. maritimum. Opportunistic taxa, including Vibrio spp., may also play a role in clinical disease progression.

Application of Quantitative-PCR to Monitor Netpen Sites in British Columbia (Canada) for Tenacibaculum Species

“…It has been proposed that Tenacibaculum sp. may make up a portion of the mucosal microbiome of Atlantic salmon in seawater [ 46 ], where the presence before and after an outbreak supports that the bacteria should be considered opportunistic pathogens [ 47 , 48 ], potentially inducing tenacibaculosis through dysbiosis [ 49 , 50 , 51 ]. Of the environmental samples, OO had the most T. dicentrarchi , supporting the notion that other organisms associated with netpens can concentrate the bacteria relative to the environment [ 52 , 53 , 54 , 55 ].…”

Advancements in Characterizing Tenacibaculum Infections in Canada

“…Further studies are required as there are substantial differences between the reports from [ 7 , 47 ] including fish species and bacterial isolates used, different geographic locations, and different transmission routes, resulting in different clinical signs of infection. From Atlantic salmon post-smolts sampled at BC netpen sites, microbial profiling using the 16S rDNA sequences indicated that T. maritimum was identified in healthy, diseased, and post-treated fish [ 123 ]. Diseased fish had reduced microbial diversities with two sequence variants of T. maritimum dominating the community [ 123 ].…”

“…From Atlantic salmon post-smolts sampled at BC netpen sites, microbial profiling using the 16S rDNA sequences indicated that T. maritimum was identified in healthy, diseased, and post-treated fish [ 123 ]. Diseased fish had reduced microbial diversities with two sequence variants of T. maritimum dominating the community [ 123 ]. Surviving fish with high proportions of T. maritimum , in association with the abundance Vibrio spp.…”

“…Surviving fish with high proportions of T. maritimum , in association with the abundance Vibrio spp. and the presence of mouthrot led researchers to provide evidence that mouthrot is a complex multifactorial disease characterized by dysbiosis [ 123 ]. With several Tenacibaculum species reported to have associations with dysbiosis, more research should focus on what multifactorial processes initiate dysbiosis linked to the presence of mouthrot.…”

“…Numerous Tenacibaculum sp. infections in laboratory practices use variably concentrated infective doses, often at high concentrations (above 10 3 CFU mL −1 ), which may indicate that the bacteria are not primary pathogens, but instead other variables, including dysbiosis [ 123 ], may influence infection.…”