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Background:White syndrome, a term for scleractinian coral disease with progressive tissue loss, is known to cause depressed growth and increased morality of coral reefs in the major oceans around the world, and the occurrence of this disease has been frequently reported in the past few decades. Investigations during April to September in both 2010 and 2011 identified widespread Porites andrewsi White syndrome (PAWS) in Xisha Archipelago, South China Sea. However, the causes and etiology of PAWS have been unknown. Methodology/Principal Findings:A transmission experiment was performed on P. andrewsi in the Qilianyu Subgroup (QLY). The results showed that there was a significant (P ≤ 0.05) difference between test and control groups after 28 days if the invalid replicates were excluded. Rates of tissue loss ranged from 0.90-10.76 cm2 d-1 with a mean of 5.40 ± 3.34 cm2 d-1 (mean ± SD). Bacterial strains were isolated from the PAWS corals at the disease outbreak sites in QLY of the Xisha Archipelago, South China Sea, and included in laboratory-based infection trials to satisfy Koch’s postulates for establishing causality. Following exposure to bacterial concentrations of 105 cells mL-1, the infected colonies exhibited similar signs to those observed in the field. Using phylogenetic 16S rRNA gene analysis, classical phenotypic trait comparison, Biolog automatic identification system, MALDI-TOF mass spectrometry and MALDI Biotyper method, two pathogenic strains were identified as Vibrio alginolyticus. Conclusion/Significance:This is the first report of V. alginolyticus as a pathogenic agent of PAWS in the South China Sea. Our results point out an urgent need to develop sensitive detection methods for V. alginolyticus virulence strains and robust diagnostics for coral disease caused by this and Vibrio pathogenic bacterium in the South China Sea. [ABSTRACT FROM AUTHOR]

Vibrio alginolyticus has high genetic diversity, but little is known about the means by which it has been acquired. In this study, the distributions of mobile genetic elements (MGEs), including integrating conjugative elements (ICEs), superintegron-like cassettes (SICs), insertion sequences (ISs), and two types of transposase genes (valT1 and valT2), in 192 strains of V. alginolyticus were investigated. ICE, SIC, and IS elements, valT1, and valT2 were detected in 8.9 %, 13.0 %, 4.7 %, 9.4 %, and 2.6 % of the strains, respectively. Blast searches and phylogenetic analysis of the acquired sequences of the ICE, SIC, IS elements and transposase genes showed that the corresponding homologues were bacterial and derived from extensive sources. The high prevalences of these MGEs in V. alginolyticus implied the extensive and frequent exchange of genes with environmental bacteria and that these elements strongly contribute to the genetic and phenotypic diversity of the bacterium. To our knowledge, this is the first report of V. alginolyticus harboring ICE and SIC elements. [ABSTRACT FROM AUTHOR]

Many pathogens undergo phase variation between rugose and smooth colony morphology or between opaque and translucent colony morphology, which is mainly due to the variation in the surface polysaccharides. In this study, Vibrio alginolyticus ZJ-51 displayed phase variation between opaque, rugose colonies (Op) and translucent, smooth colonies (Tr). Unlike the vibrios reported previously, Tr cells of ZJ-51 enhanced biofilm formation and motility, but they did not differ from Op cells in the quantity of surface polysaccharides produced. Real time PCR was used to analyze the expression of the genes involved in polysaccharide biosynthesis, flagellar synthesis, and the AI-2 quorum-sensing system. The results revealed that the K-antigen capsule gene cluster (which consists of homologs to the cpsA-K in Vibrio parahaemolyticus) and O-antigen polysaccharide gene cluster (which contains homologs to the wza-wzb-wzc) were significantly more transcribed in Tr cells. The AI-2 quorum-sensing genes showed enhanced expression in the Tr variant which also exhibited greater expression of genes associated with polar flagellar biosynthesis. These results suggest that colony phase variation might affect the virulence and survival ability in the stressful environment inhabited by V. alginolyticus.