Phylogenetic analyses of Norwegian Tenacibaculum strains confirm high bacterial diversity and suggest circulation of ubiquitous virulent strains

Abstract

Tenacibaculosis is a bacterial ulcerative disease affecting marine fish and represents a major threat to aquaculture worldwide. Its aetiological agents, bacteria belonging to the genus Tenacibaculum, have been present in Norway since at least the late 1980’s and lead to regular ulcerative outbreaks and high mortalities in production of farmed salmonids. Studies have shown the presence of several Tenacibaculum species in Norway and a lack of clonality in outbreak-related strains, thus preventing the development of an effective vaccine. Hence, a thorough examination of the bacterial diversity in farmed fish presenting ulcers and the geographical distribution of the pathogens should provide important insights needed to strengthen preventive actions. In this study, we investigated the diversity of Tenacibaculum strains isolated in 28 outbreaks that occurred in Norwegian fish farms in the period 2017–2020. We found that 95% of the 66 strains isolated and characterized, using an existing MultiLocus Sequence Typing system, have not previously been identified, confirming the high diversity of this genus of bacteria in Norway. Several of these Tenacibaculum species seem to be present within restricted areas (e.g., Tenacibaculum dicentrarchi in western Norway), but phylogenetic analysis reveals that several of the strains responsible of ulcerative outbreaks were isolated from different localities (e.g., ST- 172 isolated from northern to southern parts of Norway) and/or from different hosts. Understanding their reservoirs and transmission pathways could help to address major challenges in connection with prophylactic measures and development of vaccines.

Fundamental metabolic strategies of heterotrophic bacteria

“…However, exceptions to the median metabolic preference emerged, indicated by squares in Fig. 1d, such as the acid-specialist Tenacibaculum genus in the Flavobacteriales, which includes fish pathogens (12). Conversely, the orders Pseudomonadales and Rhodobacterales (commonly thought to specialize in simple substrates (13)) tended to prefer acids (SAP < 0), but we also found the sugar-specialist Pseudomonadales genus Saccharophagus , which are known sugar degraders (14).…”

Experimental challenge of Chinook salmon withTenacibaculum maritimumandTenacibaculum dicentrarchifulfils Koch’s postulates

“…Salmon are the highest value marine fish species in the global aquaculture sector [1,2]. Since the 1980s, salmonid aquaculture has been hampered by tenacibaculosis (formerly known as marine flexibacteriosis), an economically significant marine infectious disease [3][4][5][6][7]. Tenacibaculosis is an epidermal infection caused by the biofilm-producing, Gram-negative obligate marine bacteria Tenacibaculum spp.…”

Proteomic characterization of Tenacibaculum dicentrarchi under iron limitation reveals an upregulation of proteins related to iron oxidation and reduction metabolism, iron uptake systems and gliding motility

“…Tenacibaculum dicentrarchi is a Gram-negative bacterium originally isolated from European sea bass (Dicentrarchus labrax) in Spain (Piñeiro-Vidal et al, 2012). It is currently recognized as a pathogen in various fish species in Norway (Lagadec et al, 2021;Olsen et al, 2017) and in farmed salmonids in Tasmania (Wilson et al, 2019) and Canada (Nowlan et al, 2021). Since the first report of tenacibaculosis caused by T. dicentrarchi in farmed Atlantic salmon (Salmo salar) in Chile (Avendaño-Herrera et al, 2016), the disease has become the second leading infectious cause of death in Chilean farmed fish, including Coho salmon (Oncorhynchus kisutch) and rainbow trout (Oncorhynchus mykiss) (Avendaño-Herrera et al, 2020).…”