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

Hyoun Joong Kim,Saekil Yun,Sung Bin Lee,Jun Kwon,Cheng Chi,Sang Wha Kim,Sib Sankar Giri,Woo Taek Oh,Se Chang Park,Ji Hyung Kim,Se Jin Han,Jin Woo Jun,Sang Guen Kim

doi:10.3390/pathogens9030206

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.

Highlights

Oysters are the most consumed shellfish worldwide and account for the largest commodity in the bivalve aquaculture industry
In general V. coralliilyticus, V. tubiashii and OsHV-1are known as main causative agents of the mass mortality of marine bivalve larvae [7,17,18]
Investigations made in this study on the mass mortality of Pacific oyster larvae revealed that dead and moribund larvae experienced symptoms of bacillary necrosis and adhesion of ciliates

Summary

Introduction

Oysters are the most consumed shellfish worldwide and account for the largest commodity in the bivalve aquaculture industry. Since the middle of the 2000s, there have been perpetual occurrences of mass mortality owing to bacillary necrosis in Korean oyster seedling production hatcheries. The genus Vibrio is composed of ubiquitous aquatic bacteria, including diverse members of planktonic and animal-associated microbial communities [2]. Several organisms in this genus, such as V. alginolyticus, V. anguillarum, V. splendidus biovarII, V. tubiashii, and V. coralliilyticus, have been associated with mass mortalities in nursery cultures of juvenile bivalves at oyster hatcheries worldwide [3,4,5,6,7]. All of the abovementioned species have been implicated in bacillary necrosis, V. tubiashii has been identified as one of the most critical marine bacteria causing the well characterized adverse effect [8]. While V. tubiashii and V. coralliilyitcus exhibit similar virulence in the Eastern oyster, V. coralliilyticus-induced mortality is far greater than V. tubiashii-induced mortality in the Pacific oyster [9]

Methods

Results

Conclusion