Isolation and Characterization of Two Bacteriophages and Their Preventive Effects against Pathogenic Vibrio coralliilyticus Causing Mortality of Pacific Oyster (Crassostrea gigas) Larvae.

Hyoun Joong Kim,Se Chang Park,Jun Kwon,Sung Bin Lee,Sib Sankar Giri,Sang Wha Kim,Sang Guen Kim

doi:10.3390/microorganisms8060926

Abstract

Vibrio coralliilyticus is one of the major pathogens causing mass mortality in marine bivalve larvae aquaculture. To prevent and control Vibrio spp. infections in marine bivalve hatcheries, various antibiotics are overused, resulting in environmental pollution and the creation of multi-drug-resistant strains. Therefore, research on the development of antibiotic substitutes is required. In this study, we isolated two bacteriophages (phages) that specifically infected pathogenic V. coralliilyticus from an oyster hatchery and designated them as pVco-5 and pVco-7. Both phages were classified as Podoviridae and were stable over a wide range of temperatures (4–37 °C) and at pH 7.0–9.0. Thus, both phages were suitable for application under the environmental conditions of an oyster hatchery. The two phages showed confirmed significant bactericidal efficacy against pathogenic V. coralliilyticus in an in vitro test. In the in vivo experiment, the phage pre-treated groups of Pacific oyster larvae showed significantly lower mortality against V. coralliilyticus infection than untreated control larvae. The results of the present study suggest that both phages could be used in the artificial marine bivalve seedling industry; not only to prevent pathogenic V. coralliilyticus infection, but also to reduce antibiotic overuse.

Highlights

Asia has the highest yields of oysters in the world
The average diameter of pVco-5 was 54.96 ± 2.07 nm (n = 20) and that of pVco-7 was 60.71 ± 3.55 nm. Both pVco-5 and pVco-7 showed an icosahedral capsid with a short non-contractile tail. This means that both phages are classified as Podoviridae based on the morphological classification system proposed by Ackermann [40] (Figure 1)
Phages are viruses that invade bacteria, and lytic phages are widely used as biocontrol agents because of their bactericidal activity

Summary

Introduction

Asia has the highest yields of oysters in the world. In 2017 it produced 5,435,627 tons, 95.19% of the global production (5,710,522 tons) [1]. Since the development of marine bivalve artificial seed production technology, numerous countries have produced seedlings of various species. In Korea, the artificial seedling production industry for Pacific oysters has actively developed, mainly in the southern region. The Republic of Korea produced 315,255 tons of Pacific oysters (Crassostrea gigas), 49.33% of the global production (639,030 tons) [1], making it the largest producer of Pacific oysters in the world. Since the mid-2000s, outbreaks of Vibrio coralliilyticus and Ostreid Herpesvirus-1 uVar (OsHV-1 uVar) have led to frequent mass mortalities of Pacific oysters in Korea [2,3,4,5]

Methods

Results

Conclusion