Defensins are abundant in cells and tissues that are involved in host defense against microbialinfections. zfDB3 (zebrafish β-defensin 3) is one of 3 copies of defensin β-like genes from zebrafish (Daniorerio). Here we focus on mzfDB3, which is the gene encoding for the zebrafish β-defensin 3 mature peptide.A codon-optimized mzfDB3 gene with a 6×His-tag at the 3′-end was inserted into the pPICZαA expressionvector and transformed into Pichia pastoris X-33 cells. The recombinant zebrafish β-defensin 3 mature pep-tide (rmzfDB3) was induced with 1.0% methanol at 29°C for 72 h and purified by immobilized metal affinitychromatography. MALDI-TOF/TOF analysis confirmed the expected purified product (rmzfDB3,5.9 kDa). Fermentation supernatant, which contained rmzfDB3, showed antibacterial activity against Gram-positive (i.e., Listeria monocytogenes, Staphylococcus aureus, and Bacillus cereus) and Gram-negative (i.e.,Escherchia coli BL21, Vibrio parahaemolyticus, Salmonella lignieres, and Pseudomonas aeruginosa) bacteria.

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• Expression of the Zebrafish β-defensin 3 Mature Peptidein Pichia pastoris and Its Purification and Antibacterial Activity