Isolation of a virulent Vibrio alginolyticus Bacteriophage and Its Application in Shrimp culture

As an opportunist pathogen, Vibrio alginolyticus , causes disease outbreaks in marine farmed fish and invertebrates. Due to problems caused by the abuse of antibiotics, it is extremely important to develop green biocontrol methods for Vibrio diseases. Phage therapy is considered a safe and promising prevention and treatment method. Here, we report that a novel virulent bacteriophage VaPW, which infects V. alginolyticus , was isolated from seawater. The bacteriophage is morphologically similar to phages from Myoviridae family. It displayed good pH (7–9) and temperature (≤ 50°C) tolerance and had a narrow host range. Its genome consists of 34,637 bp with a GC content of 43.22%, while sequence analysis revealed the presence of 41 potential ORFs, of which 26 coding sequences showed homology to functionally characterized genes. The in vitro antibacterial experiment showed that phage VaPW could effectively inhibit the growth of V. alginolyticus ATCC 33787. Moreover, the shrimp survival test demonstrated that phage VaPW has the in vivo protection effect against V. alginolyticus infection. To determine whether the putative lysozyme and holin from phage VaPW have bactericidal activity, orf26 and orf27 were cloned for protein expression and analyses in E. coli . The data revealed that co-existence of holin and lysozyme exhibited a synergistic bactericidal effect on the lysis of target cells compared with single protein alone. These results suggest that phage VaPW and its proteins may provide good candidates to control recurrent diseases caused by V. alginolyticus in marine animals.