A Novel Antimicrobial Peptide Sparanegtin Identified in Showing Antimicrobial Activity and Immunoprotective Role In Vitro and Vivo.

The abuse of antibiotics in aquaculture and livestock no doubt has exacerbated the increase in antibiotic-resistant bacteria, which imposes serious threats to animal and human health. The exploration of substitutes for antibiotics from marine animals has become a promising area of research, and antimicrobial peptides (AMPs) are worth investigating and considering as potential alternatives to antibiotics. In the study, we identified a novel AMP gene from the mud crab and named it Sparanegtin. transcripts were most abundant in the testis of male crabs and significantly expressed with the challenge of lipopolysaccharide (LPS) or . The recombinant Sparanegtin (rSparanegtin) was expressed in and purified. rSparanegtin exhibited activity against Gram-positive and Gram-negative bacteria and had potent binding affinity with several polysaccharides. In addition, rSparanegtin exerted damaging activity on the cell walls and surfaces of with rougher and fragmented appearance. Interestingly, although rSparanegtin did not show activity against in vitro, it played an immunoprotective role in and exerted an immunomodulatory effect by modulating several immune-related genes against infection through significantly reducing the bacterial load in the gills and hepatopancreas and increasing the survival rate of crabs.