Antibacterial Activity of Bacillus Strains against Acute Hepatopancreatic Necrosis Disease-Causing Vibrio campbellii in Pacific White Leg Shrimp

Abstract

Acute hepatopancreatic necrosis disease (AHPND) is a bacterial disease caused by Vibrioparahaemolyticus. Currently, various Vibrio strains, including V. campbellii, V. owensii, and V. harveyi, have been reported as causative pathogens. Thus, controlling AHPND to maintain high production in shrimp aquaculture is difficult. We evaluated the antimicrobial activity of five Bacillus strains (B1, B3, B5, B7, and B8)—isolated from seawater in Jeju, South Korea—against 12 Vibrio strains (10 AHPND strains and 2 non-AHPND strains). All tested Bacillus strains inhibited the growth of at least one of the tested Vibrio strains in the dot-spot method. Among them, B1 and B3, the most effective Bacillus strains against the Vibrio strains, particularly against AHPND-causing V. campbellii (VcAHPND), were further used in a challenge test. After 48–60 h of VcAHPND immersion, a significantly higher survival rate was observed in the B1-treated group (100%) than in the non-Bacillus-treated group (64.3%). Based on the qPCR analysis of AHPND, the cycle threshold values were 31.63 ± 0.2 (B1-treated group) and 38.04 ± 0.58 (B3-treated group), versus 28.70 ± 0.42 in the control group. Genome sequencing and phylogenetic analysis revealed that B1 and B3 were classified as B. velezensis. The 16S rRNA sequences and complete genome sequences of B1 and B3 were deposited in GenBank.