In Tasmania (Australia), during the marine phase, it has been observed that flesh pigmentation significantly drops in summer, possibly due to high water temperatures (> 20°C). Although this deleterious effect of summer temperatures has been ascertained, there is a lack of knowledge of the actual mechanisms behind the impaired uptake and/or loss of pigments in Atlantic salmon in a challenging environment. Since the microbial community in the fish intestine significantly changes in relation to the variations of water temperature, this study was conducted to assess how the gut microbiota profile also correlates with the flesh color during temperature fluctuation. We sampled 68 fish at three time points covering the end of summer to winter at a marine farm in Tasmania, Australia. Flesh color was examined in two ways: the average color throughout and the evenness of the color between different areas of the fillet. Using 16S rRNA sequencing of the v3-v4 region, we determined that water temperature corresponded to changes in the gut microbiome both with alpha diversity (Kruskal-Wallis tests P = 0.05) and beta diversity indices (PERMANOVA P = 0.001). Also, there was a significant correlation between the microbiota and the color of the fillet (PERMANOVA P = 0.016). There was a high abundance of Pseudoalteromonadaceae, Enterobacteriaceae, Microbacteriaceae, and Vibrionaceae in the pale individuals. Conversely, carotenoid-synthesizing bacteria families (Bacillaceae, Mycoplasmataceae, Pseudomonas, Phyllobacteriaceae, and Comamonadaceae) were found in higher abundance in individuals with darker flesh color.

The Atlantic salmon (Salmo salar L., 1758) is a temperate fish species native to the northern Atlantic Ocean. The distinctive pink–red flesh color (i.e., pigmentation) significantly affects the market price. Flesh paleness leads to customer dissatisfaction, a loss of competitiveness, a drop in product value and, consequently, severe economic losses. This work extends our knowledge on salmonid carotenoid dynamics to include the interaction between the gut microbiota and flesh color. A significant association between the flesh color and abundance of specific bacterial communities in the gut microbiota suggests that color may be affected either by seeding resilient beneficial bacteria or by inhibiting the negative effect of pathogenic bacteria. We sampled 96 fish, which covered all phenotypes of flesh color, including the average color and the evenness of color of different areas of the fillet, at both the distal intestine and the pyloric caeca of each individual, followed by 16S rRNA sequencing at the V3-V4 region. The microbiota profiles of these two gut regions were significantly different; however, there was a consistency in the microbiota, which correlated with the flesh color. Moreover, the pyloric caeca microbiota also showed high correlation with the evenness of the flesh color (beta diversity index, PERMANOVA, p = 0.002). The results from the pyloric caeca indicate that Carnobacterium, a group belonging to the lactic acid bacteria, is strongly related to the flesh color and the evenness of the color between the flesh areas.

Literature on the cuticle formation in larval stages of the diverse group of decapod crustaceans is lacking, as opposed to a wealth of knowledge in several insect groups. Here we provide the first glimpse of the cuticular organisation in larvae of the eastern spiny lobster Sagmariasus verreauxi . A bioinformatic approach applied to S . verreauxi transcriptome through metamorphosis identified for the first time a small secreted protein with multiple isoforms that is highly expressed in crustacean larvae. This protein, named crustacean larval factor (Clf) shares structural characteristics with insect follicle cell protein 3 (FCP3), an insect-specific, rapidly evolving protein, with spatial-temporal regulated expression that is restricted to follicular cells during the production of the vitellin coat. Furthermore, we identified the FCP3 domain in additional structural proteins in multiple arthropod groups. Recombinant Clf inhibited in vitro calcium carbonate crystalline precipitation, in keeping with the finding that the spiny lobster larval cuticle is mainly composed of amorphous calcium carbonate. In addition, the recombinant Clf was shown to bind chitosan. Taken together, this research identifies two novel structural domains with lineage-specific expansion across arthropods. In crustaceans, Clf is found predominantly in larvae and the spatial-temporal regulated FCP3 factor occurs as a domain identified in multiple structural proteins across arthropods. Given the shared ten cysteines backbone between the Clf and FCP domains, a shared evolution is suggested and should be further explored.

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Streptococcal pathogens, particularly Streptococcus iniae, are emerging as a major cause of meningitis and septicaemia in a broad range of farmed and wild fish species, and are occasionally zoonotic. The major virulence factor in fish pathogenic streptococci is a highly variable antigenic polysaccharide capsule, which has resulted in serotype switching and reinfection of previously vaccinated fish. Therefore there is an urgent need to investigate more highly conserved protein-based critical virulence factors as targets for new vaccines.Complement proteases C5a peptidase and C3 protease of S. iniae were investigated in the present study to determine their role in virulence, as they are both secreted or surface associated and may represent potential targets for vaccination. My research shows that the C5a peptidase (scpI) and C3 protease (cppA) are inversely regulated with capsular polysaccharide. This coordinate regulation allows the capsule to be down-regulated to permit attachment to hydrophobic surfaces which may be essential for invasion of the Central Nervous System (CNS) and rapid onset of meningitis, whilst the proteases are upregulated to protect the bacteria from complement-enhanced killing by neutrophils in barramundi whole blood assays. Knockout mutants deficient in each of the genes revealed reduced growth in whole blood, serum and antiserum. Moreover, these mutants revealed a role for ScpI and CppA in the interruption of the classical pathway since they were susceptible to the antiserum, which contained specific antibodies and complement proteins activating the classical pathway. Additional work to determine whether blood and serum resistance can be rescued by complementing the knockout mutants is required. To explore environmental factors in the host that may drive coordinate regulation of scpI and cppA with capsular polysaccharide synthesis protein E (cpsE) iron limitation was investigated.Iron stress appeared to be as one of the triggers for reduction the expression of capsule and coordinate increase in complement proteases expression. Future work should elucidate further environmental cues in the host that regulate expression of these genes, as it is likely to be complex and multifactorial. Together, these data implicate complement proteases in survival and dissemination in the host and therefore warrant further investigation as conserved protein targets for vaccines for farmed fish.