A novel antimicrobial peptide Larimicin from large yellow croaker (Larimichthys crocea) shows potent antibacterial activity in vitro and enhances resistance to vibrio fluvialis infection in vivo.

Antimicrobial peptides (AMPs) are considered a key component of innate immunity, playing a vital role in host defense. In the study, a novel functional gene, named Larimicin, was identified from large yellow croaker Larimichthys crocea. The Larimicin gene was widely distributed in multiple tissues of healthy L. crocea and was significantly induced in the liver after Vibrio alginolyticus or Vibrio parahaemolyticus infection. Larimicin, a truncated peptide derived from Larimicin, showed broad-spectrum antimicrobial activity and a binding affinity with LPS. It exhibited effective bactericidal activity against the common aquatic pathogens Vibrio fluvialis, Pseudomonas fluorescens, and Pseudomonas putida. It also showed anti-biofilm activity against three aquatic pathogens. Moreover, Larimicin disrupted the integrity of the outer and inner membranes, resulting in ATP leakage and intracellular ROS accumulation, which ultimately led to bacterial cell death. Larimicin exhibited good thermal stability and cation tolerance, with no obvious cytotoxicity or hemolytic activity. Notably, Larimicin significantly improved the survival rate of L. crocea infected with V. fluvialis, raising it to 95 %, indicating its anti-infective role in vivo. In addition, Larimicin significantly reduced the expression of the pro-inflammatory cytokines TNF-α and IL-1β, while up-regulating the anti-inflammatory factor IL-4 mRNA level. It also elevated the expression levels of piscidin, hepcidin, and lysozyme, as well as enhanced the enzymatic activity of lysozyme. Taken together, Larimicin is a potential antibacterial agent for use in aquaculture to combat V. fluvialis infection diseases in the future.