Abstract
Capsule-forming extracellular polysaccharides are crucial for bacterial host colonization, invasion, immune evasion, and ultimately pathogenicity. Due to warming ocean waters and human encroachment of coastal ecosystems, Vibrio parahaemolyticus has emerged as a globally important foodborne enteropathogen implicated in acute gastroenteritis, wound infections, and septic shock. Conventionally, the antigenic properties of lipopolysaccharide (LPS, O antigen) and capsular polysaccharide (CPS, K antigen) have provided a basis for serotyping V. parahaemolyticus, whereas disclosure of genetic elements encoding 13 O-serogroups have allowed molecular serotyping methods to be developed. However, the genetic structure of CPS loci for 71 K-serogroups has remained unidentified, limiting progress in understanding its roles in V. parahaemolyticus pathophysiology. In this study, we identified and characterized the genetic structure and their evolutionary relationship of CPS loci of 40 K-serogroups through whole genome sequencing of 443 V. parahaemolyticus strains. We found a distinct pattern of CPS gene cluster across different K-serogroups and expanded its new 3′-border by identifying glpX as a key gene conserved across all K-serogroups. A total of 217 genes involved in CPS biosynthesis were annotated. Functional contents and genetic structure of the 40 K-serogroups were analyzed. Based on inferences from species trees and gene trees, we proposed an evolution model of the CPS gene clusters of 40 K-serogroups. Horizontal gene transfer by recombination from other Vibrio species, gene duplication is likely to play instrumental roles in the evolution of CPS in V. parahaemolyticus. This is the first time, to the best of our knowledge, that a large scale of CPS gene clusters of different K-serogroups in V. parahaemolyticus have been identified and characterized in evolutionary contexts. This work should help advance understanding on the variation of CPS in V. parahaemolyticus and provide a framework for developing diagnostically relevant serotyping methods.
Highlights
Vibrio parahaemolyticus, a Gram-negative halophilic bacterium, is taxonomically a notable member of the genus Vibrio within the family Vibrionaceae
The average N50 length and average N90 length of assembled contigs are 335.44 and 59.48 kbp, respectively. Draft genomes of these 443 V. parahaemolyticus strains were subjected to capsular polysaccharide (CPS) loci gene cluster sequence extraction for subsequent analysis
Our findings have provided new insights into the global evolution and diversity of CPS gene cluster (CPSgc) of V. parahaemolyticus
Summary
A Gram-negative halophilic bacterium, is taxonomically a notable member of the genus Vibrio within the family Vibrionaceae. It prevails in estuarine, marine, and coastal areas (Su and Liu, 2007; Nelapati et al, 2012; Ceccarelli et al, 2013; Zhang and Orth, 2013), and is typically isolated in a freeswimming state. Because of climate change and anthropogenic degradation of coastal environments, V. parahaemolyticus is gaining notoriety as an enteropathogen in humans worldwide, where people depend on seafood as a major nutritional source. It can cause three major diseases, namely, gastroenteritis, wound infections, and septicemia (Daniels et al, 2000). Thermostable direct hemolysin (TDH) and TDH-related hemolysin (TRH) are two major virulence factors of V. parahaemolyticus implicated in its pathogenicity (Wang et al, 2015)
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