Immunomulation effect of alginic acid and chitooligosaccharides in silver carp (Hypophthalmichthys molitrix)

Structural characterization and immune-enhancing effects of a novel polysaccharide extracted from Sargassum fusiforme

To alleviate the adverse effects of chemotherapy and bolster immune function, a novel polysaccharide derived from Sargassum fusiforme named as SFP-αII. The structural composition of SFP-αII predominantly consisted of guluronic and mannuronic acids in a molar ratio of 33.8:66.2, with an average molecular weight of 16.5 kDa. Its structure was primarily characterized by →4)-α-GulA-(1 → and →4)-β-ManA-(1 → linkages confirmed by FT-IR, methylation, and NMR analyses. The absence of a triple-helix structure was in SFP-αII was confirmed using circular dichroism and Congo red dye assays. The dimensions varied with lengths ranging from 20 nm up to 3 μm revealed by atomic force microscopy (AFM). SFP-αII has been found to enhance immunomodulatory activity in cyclophosphamide (CTX)-induced immunosuppressed mice. This was evidenced by improvements in immune organ indices, cytokine levels, and the release of nitric oxide (NO). Specifically, SFP-αII mitigated immunosuppression by upregulating the secretion of IL-1β (167.3 %) and TNF-α (227.1 %) at a dose of 400 mg/kg, compared with the CTX group in macrophages. Ultimately, SFP-αII may serve as a mechanism for immune enhancement through modulation of TLR4-mediated NF-κB and MAPK signaling pathways. This integration of traditional Chinese and Western medicine, leveraging SFP-αII as a potential functional food could be pivotal in alleviating immunosuppressive side effects in CTX treatment.

Effects of phoxim on antibacterial infection of silver carp

The efficacy of phoxim in treating bacterial sepsis in silver carp is significant, yet its underlying mechanism remains elusive. This study aimed to establish a model of Aeromonas veronii infection in silver carp and subsequently treat the infected fish with 10 μg/L phoxim. Kidney and intestine samples from silver carp were collected for transcriptome analysis and assessment of intestinal microbial composition, with the aim of elucidating the mechanism underlying the efficacy of phoxim in treating bacterial sepsis in silver carp. The results of transcriptome and intestinal microbial composition analysis of silver carp kidney indicated that A. veronii infection could up-regulate the expression of il1β, il6, nos2, ctsl, casp3 et al., which means, signifying that the kidney of silver carp would undergo inflammation, induce apoptosis, and alter the composition of intestinal microorganisms. Phoxim immersion might enhance the energy metabolism of silver carp and change its intestinal microbial composition, potentially elevating the antibacterial infection resistance of silver carp. These findings may contribute to an understanding of how phoxim can effectively treat bacterial sepsis in silver carp.

Chitosan oligosaccharide accelerates the dissemination of antibiotic resistance genes through promoting conjugative plasmid transfer

The dissemination of antibiotic resistance genes (ARGs), especially via plasmid-mediated horizontal gene transfer, poses a pervasive threat to global health. Chitosan-oligosaccharide (COS) is extensively utilized in medicine, plant and animal husbandry. However, their impact on microflora implies the potential to exert selective pressure on plasmid transfer. To explore the role of COS in facilitating the dissemination of ARGs via plasmid conjugation, we established in vitro mating models. The addition of COS to conjugation mixtures significantly enhanced the transfer of RP4 plasmid and mcr-1 positive IncX4 plasmid in both intra- and inter-specific. Phenotypic and transcriptome analysis revealed that COS enhanced intercellular contact by neutralizing cell surface charge and increasing cell surface hydrophobicity. Additionally, COS increased membrane permeability by inhibiting the Tol-Pal system, thereby facilitating plasmid conjugative transfer. Furthermore, COS served as the carbon source and was metabolized by E. coli, providing energy for plasmid conjugation through regulating the expression of ATPase and global repressor factor-related genes in RP4 plasmid. Overall, these findings improve our awareness of the potential risks associated with the presence of COS and the spread of bacterial antibiotic resistance, emphasizing the need to establish guidelines for the prudent use of COS and its discharge into the environment.

Chitin, chitosan and chitooligosaccharides as potential growth promoters and immunostimulants in aquaculture: A comprehensive review

There is a stable growth in aquaculture production to avoid seafood scarcity. The usage of eco-friendly feed additives is not only associated with aquatic animal health but also reduces the risk of deleterious effects to the environment and consumers. Aquaculture researchers are seeking dietary solutions to improve the growth performance and yield of target organisms. A wide range of naturally derived compounds such as probiotics, prebiotics, synbiotics, complex carbohydrates, nutritional factors, herbs, hormones, vitamins, and cytokines was utilized as immunostimulants in aquaculture. The use of polysaccharides derived from natural resources, such as alginate, agar, laminarin, carrageenan, fucoidan, chitin, and chitosan, as supplementary feed in aquaculture species has been reported. Polysaccharides are prebiotic substances which are enhancing the immunity, disease resistance and growth of aquatic animals. Further, chitin (CT), chitosan (CTS) and chitooligosaccharides (COS) were recognized for their biodegradable properties and unique biological functions. The dietary effects of CT, CTS and COS at different inclusion levels on growth performance, immune response and gut microbiota in aquaculture species has been reviewed. The safety regulations, challenges and future outlooks of CT, CTS and COS in aquatic animals have been discussed in this review.

Effects of Jerusalem Artichoke (Helianthus tuberosus) as a Prebiotic Supplement in the Diet of Red Tilapia (Oreochromis spp.)

The aim of the present study was to evaluate the effects of a Jerusalem artichoke-supplemented diet on the blood chemistry, growth performance, intestinal morphology, expression of antioxidant-related genes, and disease resistance against Aeromonas veronii challenge in juvenile red tilapia. A completely randomized design (CRD) was followed to feed red tilapias with three experimental diets: control, 5.0 g/kg JA-supplemented (JA5), or 10.0 g/kg JA-supplemented (JA10) diets in triplicates for 4 weeks. The results revealed that the growth performance, weight gain (WG), specific growth rate (SGR), and average daily gain (ADG) of fish fed diets JA5 and JA10 were significantly higher (p < 0.05) than those of fish fed the control diet. Fish fed the control diet had significantly higher T-bilirubin, D-bilirubin, and ALT in blood serum than fish fed JA5 and JA10, as well as higher BUN than fish fed JA5. The number of goblet cells in the proximal and distal parts of the intestine revealed that the number of acid, neutral, and double-staining mucous cells of fish fed diets JA5 and JA10 was significantly higher (p < 0.05) than in fish fed the control diet. The diets including the prebiotic (JA5 and JA10) were associated with a significant increase in the expression of gpx1 and gst antioxidant-related genes and disease resistance against A. veronii in juvenile red tilapia. Therefore, JA5 and JA10 can be employed as promising prebiotics for sustainable red tilapia farming.