Identification and Genome Analysis of Vibrio coralliilyticus Causing Mortality of Pacific Oyster (Crassostrea gigas) Larvae

Abstract

Vibrio coralliilyticus is known as a coral pathogen that also infects marine bivalve larvae worldwide. It is considered to be one of the major constraints in artificial marine bivalve seed production as it causes mortality. In this study, we first isolated and characterized a high virulent of V. coralliilyticus designated as SNUTY-1 that was the cause of Pacific oyster larvae mortality in Korea. In the pathogenicity test, exposure to 2.14 × 105 CFU/mL for 24 h caused mortality to 88.65 ± 2.4% of the tested healthy Pacific oyster larvae. SNUTY-1 showed anti-microbial resistance to β-lactams, such as penicillins, cephalosporins, and carbapenems. We sequenced and assembled the complete genome of SNUTY-1 (5,842,676 bp), consisting of two chromosomes (Chr I and Chr II) and two plasmids (pSNUTY1 and pSNUTY2). The COG functional analysis confirmed that Chr I had more genes associated with basic cellular functions in comparison to Chr II. The results of the phylogenetic trees based on OrthoANI values indicated that the SNUTY-1 was closely related to V. coralliilyticus strains. SNUTY-1 had a unique plasmid (pSNUTY2), which could mean that the Korean isolate is different from other sequenced V. coralliilyticus strains from different geographical origins. Toxic proteins such as cytolysin/hemolysin and extracellular metalloprotease genes were encoded on Chr I and Chr II of SNUTY-1. These data facilitate the control of V. coralliilyticus infections in aquaculture by providing valuable insights into the biodiversity of this organism and valuable information for the study of virulence factors.

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

“…Since the development of artificial seedling cultures, the production of marine bivalves has been increasing worldwide. However, pathogens such as V. coralliilyticus, V. tubiashii, and OsHV-1 can cause substantial economic losses [4,5,[8][9][10]41]. Unlike vertebrates, bivalves do not have an acquired immune system, ruling out the use of agents such as vaccines and severely limiting the options for prevention and treatment of infections.…”

“…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. However, 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].…”

Bacteriophage Cocktail for the Prevention of Multiple-Antibiotic-Resistant and Mono-Phage-Resistant Vibrio coralliilyticus Infection in Pacific Oyster (Crassostrea gigas) Larvae

“…Five-day-old healthy Pacific oyster larvae (100–140 µm) were used to confirm the pathogenicity of the phage-resistant variant. A challenge test was performed as previously described by Kim et al [ 4 ]. Oyster larvae ( n = 50 ± 13) were placed into each well of a 6-well cell culture plate (SPL, Pocheon, Korea) with 10 mL of 32 practical salinity units (psu) of filtered and sterilized seawater (FSS).…”

“…However, diseases in marine bivalve hatcheries that occur due to Vibrio sp. [ 2 , 3 , 4 , 5 , 6 ] and Ostreid Herpesvirus-1 [ 7 , 8 , 9 , 10 , 11 , 12 ] infections cause economic losses worldwide.…”

“…In marine bivalve hatcheries, Vibrio coralliilyticus ( V. coralliilyticus ) is one of the major causative agents of drastic mass mortality in a short period when larvae are at the free-swimming stage [ 4 , 5 , 13 ]. To control V. coralliilyticus infection in marine bivalve hatcheries, many studies have been conducted on the application of various antibiotics, noting problems such as the occurrence of antibiotic-resistant variants and environmental pollution due to the indiscriminate use of antibiotics in seedling production facilities [ 14 , 15 ].…”