Marine antimicrobial peptide tilapia piscidin (TP) 4 possesses antibacterial and immune regulatory activities, making it a potentially valuable feed supplement in aquaculture. In this study, we expressed the TP4 peptide, originally identified from Oreochromis niloticus, in yeast (Pichia pastoris) under the control of an alcohol oxidase (Aox) 1 promoter. Recombinant (r)TP4 expression was induced by methanol. Transformation was confirmed by PCR, and expression was confirmed by colony hybridization. For scalable production, transformed yeast was cultured and induced in a bench-top fermenter bioreactor system under controlled conditions. The rTP4-expressing yeast cells were then pelleted and fed to 28-day-old Lates calcarifer as a 0, 1, 3 or 5 % supplement to the normal diet. Growth performance and immune response were monitored in the fish for four weeks. The 3 and 5 % rTP4-yeast groups showed significant improvements in weight gain, feed efficiency, survival, protein efficiency ratio, and hepatosomatic index. In addition, rTP4-yeast increased the levels of IgM, which plays a critical role in innate immunity. Furthermore, rTP4-yeast-containing diet elevated SOD, GPx and catalase activities. Since feeding L. calcarifer with bioreactor-produced rTP4-expressing yeast significantly enhanced growth and immunity, rTP4 should be considered for use as a functional feed supplement to replace excessively administered antibiotics in farmed fish.
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