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In this study, we have identified a novel peptide NV14 with antioxidative functions from serine O‐acetyltransferase (SAT) of Artrospira platensis (Ap). The full sequence of ApSAT and its derived NV14 peptide “NVRIGAGSVVLRDV” (141–154) was characterized using bioinformatics tools. To address the transcriptional activity of ApSAT in response to induce generic oxidative stress, the spirulina culture was exposed to H2O2 (10 mM). The ApSAT expression was studied using RT‐PCR across various time points and it was found that the expression of the ApSAT was significantly upregulated on Day 15. The in vitro cytotoxicity assay against NV14 was performed in human dermal fibroblast cells and human blood leukocytes. Results showed that NV14 treatment was non‐cytotoxic to the cells. Besides, in vivo treatment of NV14 in zebrafish larvae did not exhibit the signs of developmental toxicity. Further, the in vitro antioxidant assays enhanced the activity of the antioxidant enzymes, such as SOD and CAT, due to NV14 treatment; and also significantly reduced the MDA levels, while increasing the superoxide radical and H2O2 scavenging activity. The expression of antioxidant enzyme genes glutathione peroxidase, γ‐glutamyl cysteine synthase, and glutathione S‐transferase were found to be upregulated in the NV14 peptide pretreated zebrafish larvae when induced with generic oxidative stress, H2O2. Overall, the study showed that NV14 peptide possessed potent antioxidant properties, which were demonstrated over both in vitro and in vivo assays. NV14 enhanced the expression of antioxidant enzyme genes at the molecular level, thereby modulating and reversing the cellular antioxidant balance disrupted due to the H2O2‐induced oxidative stress.

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Bacterial virulence factors play a major role in infection, which provides devastating effect on the aquaculture industry. Bacterial toxins are the major virulence factors that influence the roles of host cells and take control of living organisms’ vital processes to facilitate microbial infection. Various other bacterial virulent components such as adhesins, capsular polysaccharides, lipopolysaccharides, bacterial flagellum, pili and microbial siderophore provide a diverse effect in the microbial pathogenesis and express a variety of pathogenic molecules including aebABCEG, HutA, cpsD and pPHDD1. Bacterial protein secretion system secretes enzymes and toxins from bacterial cytoplasm to the host membrane targeting the immune cells and promoting biofilm formation. However, as they enter, the host body expresses various immune molecules that interact to utilize the pathogen recognition receptors. Toxins are powerful molecules formed by a broad range of bacterial pathogens attacking host cells and playing key roles in the dialogue between host and pathogen. They are important virulence factors that are often enough to decide the outcome of the infection. Hence, a detailed view on the virulence molecules majorly exotoxins from various bacterial pathogenic strains that are necessary to understand the pathogenesis. This review focuses on bacterial toxins and various other virulence factors, which influence the pathogenesis in fish.