Bacteriomic Profiling of Branchial Lesions Induced by Neoparamoeba perurans Challenge Reveals Commensal Dysbiosis and an Association with Tenacibaculum dicentrarchi in AGD-Affected Atlantic Salmon (Salmo salar L.)

Abstract

Amoebic gill disease is a parasitic condition that commonly affects marine farmed Atlantic salmon. The causative agent, Neoparamoeba perurans, induces a marked proliferation of the gill mucosa and focal superficial necrosis upon branchial lesions. The effect that amoebic branchialitis has upon gill associated commensal bacteria is unknown. A 16S rRNA sequencing approach was employed to profile changes in bacterial community composition, within amoebic gill disease (AGD)-affected and non-affected gill tissue. The bacterial diversity of biopsies with and without diseased tissue was significantly lower in the AGD-affected fish compared to uninfected fish. Furthermore, within the AGD-affected tissue, lesions appeared to contain a significantly higher abundance of the Flavobacterium, Tenacibaculum dicentrarchi compared to adjunct unaffected tissues. Quantitative PCR specific to both N. perurans and T. dicentrarchi was used to further examine the co-abundance of these known fish pathogens. A moderate positive correlation between these pathogens was observed. Taken together, the present study sheds new light on the complex interaction between the host, parasite and bacterial communities during AGD progression. The role that T. dicentrarchi may play in this complex relationship requires further investigation.

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 ].…”

Quantitative PCR for Tenacibaculum dicentrarchi and T. finnmarkense

“…2020) indicated that the Tenadi assay also detected several other Tenacibaculum species. Other PCR and qPCR assays to distinguish T. dicentrarchi are available (Slinger et al., 2020; Wilson et al., 2019); like the DICEN and FIN assays, they have not been validated in other studies.…”

Advancements in Characterizing Tenacibaculum Infections in Canada

“…A new T. dicentrarchi PCR-specific assay was developed for multiplex-PCR due to the Tenadi assay amplicon being of a similar size to other species-specific PCR assays [ 76 ]; however, validation in other studies is needed. A 16S rDNA qPCR assay has been developed to identify T. dicentrarchi and was reported to be specific but needs to be validated and investigated for potential false positives [ 79 ]. MLSA demonstrated that T. dicentrarchi is in Clade two and was the phylogenetic sister to T. ovolyticum and T. soleae [ 35 ].…”

“…All the fish were reported to have extensive scale loss, small hemorrhagic lesions, ascites, and dark livers [ 120 ]. Recently, exposure trials of Atlantic salmon to Neoparamoeba perurans (causative agent of amoebic gill disorder) identified a weak positive correlation between the presence of N. perurans and T. dicentrarchi in diseased fish [ 79 ]. In some lesions of diseased fish, 70.7% of the mean bacterial abundance was T. dicentrarchi , and there was reduced species richness and diversity indexes in diseased fish compared to naïve fish, supporting that dysbiosis may have implications for tenacibaculosis [ 79 ].…”

“…Recently, exposure trials of Atlantic salmon to Neoparamoeba perurans (causative agent of amoebic gill disorder) identified a weak positive correlation between the presence of N. perurans and T. dicentrarchi in diseased fish [ 79 ]. In some lesions of diseased fish, 70.7% of the mean bacterial abundance was T. dicentrarchi , and there was reduced species richness and diversity indexes in diseased fish compared to naïve fish, supporting that dysbiosis may have implications for tenacibaculosis [ 79 ]. In another recent study, two isolates (QCR29 and QCR41) at 3.1 and 3.7 × 10 4 CFU mL −1 were exposed to red conger eel (n = 12) for 2 h through bath exposure [ 121 ].…”