Project description:Seaweeds may represent immunostimulants that could be used as health-promoting fish feed components thereby offering an alternative for the use of antibiotics. This study was performed to gain insights into the immunomodulatory effects of dietary seaweeds in Atlantic salmon. Specifically tested were 10% inclusion levels of Laminaria digitata (SW1) and a commercial blend of seaweeds (Oceanfeed®) (SW2) against a fishmeal based control diet (FMC). Differences between groups were assessed in growth, feed conversion ratio (FCR) and blood parameters hematocrit (Hct) and hemoglobin (Hb). After a LPS challenge of fish representing each of the three groups, RNAseq was performed on head kidneys to determine transcriptomic differences in response to the immune activation, to our knowledge for the first time in fish in this context. Atlantic salmon fed with dietary seaweeds showed slightly higher FCRs and more homogenous growth but in general no major differences in performance in comparison with fishmeal fed fish. RNAseq resulted in ~154 million reads which were mapped against a NCBI Salmo salar reference and against a de novo assembled Salmo salar reference for analyses of expression of immune genes and ontology of immune processes among the 87,600 cDNA contigs. The dietary seaweeds provoked a more efficient immune response which involved more efficient identification of the infection site, and processing and presentation of antigens. More specifically, chemotaxis and the chemokine-mediated signaling pathway with involvement of genes such as C-C motif chemokine 19 were improved and the defense response to Gram-positive bacterium reduced. The predicted integrin alpha-2-like gene had by far the highest up-regulated expression and may therefore represent a key marker gene of the LPS immune response in salmonids. Specific Laminaria digita effects included reduction of the cytokine-mediated signalling pathway as indicated by the cytokine macrophage migration inhibitory factor, and interferon-gamma-mediated signalling as indicated by STAT1 and the gamma-interferon-inducible lysosomal thiol reductase precursor. Highly upregulated and specific for this diet was the expression of Major histocompatibility complex class I-related gene protein. The commercial blend of seaweeds caused more differential expression than Laminaria digita and improved immune processes such as receptor-mediated endocytosis, inflammatory response, cell adhesion and response to lipopolysaccharide. Particularly expression of many important immune receptors was up-regulated illustrating increased responsiveness. NF-kappa-B inhibitor alpha is an important gene that marked the difference between both seaweed diets as Laminaria digita inhibits the production of this cytokine while the blend of seaweeds stimulates it. It can be concluded that replacing fishmeal partly with seaweeds such as Laminaria digita can have important modulatory effects on the immune capacity of Atlantic salmon resulting in a more efficient immune response.

Project description:Porphyra/Pyropia seaweeds are promising sources for functional foods development, offering a rich macro- and micronutrient profiles. In New Zealand (NZ), endemic Porphyra/Pyropia species (karengo), exhibit considerable variability driven by geography, seasonality, and climate, which may influence their nutritional quality. Despite their use as traditional foods, the NZ Porphyra/Pyropia remain underutilized commercially, in part due to the lack of biomolecular characterisation, particularly their bioactive protein components, hindering evidence-based species selection for seaweed farming commercialisation and functional food development. This study presents the first proteomic characterization of three NZ Porphyra/Pyropia species: Pyropia virididentata, Pyropia cinnamomea, and Porphyra GRB complex. Mass spectrometry-based proteomics analysis identified differences in the phycobiliprotein composition among the species, with the Porphyra GRB complex containing higher levels of phycocyanin. Using the protein sequence information, in silico gastrointestinal digestion analysis predicted that phycobiliproteins from NZ Porphyra/Pyropia seaweeds can potentially release bioactive peptides capable of inhibiting angiotensin-converting enzyme (ACE) and dipeptidyl peptidase-IV (DPP-IV) activities. Sequence-based allergenicity prediction indicated possible cross-reactivity between NZ Porphyra/Pyropia β-phycoerythrin and β-phycocyanin against the β-phycocyanin allergen from spirulina, which is associated with a low incidence of allergy. Proximate analysis revealed that NZ Porphyra/Pyropia seaweeds have high protein (26–30.2 %) and carbohydrate (48.3–50.9 %) contents, and low fat and free sugar levels. Amino acid profiling further showed that NZ Porphyra/Pyropia seaweeds are relatively rich in sulphur-containing amino acids and umami-associated amino acids. Overall, these findings highlight the potential of NZ Porphyra/Pyropia seaweeds as a novel plant-based protein source for functional food applications.

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