Comparative genomic analysis of Vibrios yields insights into genes associated with virulence towards C. gigas larvae
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RESEARCH ARTICLE
Open Access
Comparative genomic analysis of Vibrios yields insights into genes associated with virulence towards C. gigas larvae Hanna Kehlet-Delgado1* , Claudia C. Häse2 and Ryan S. Mueller1
Abstract Background: Vibriosis has been implicated in major losses of larvae at shellfish hatcheries. However, the species of Vibrio responsible for disease in aquaculture settings and their associated virulence genes are often variable or undefined. Knowledge of the specific nature of these factors is essential to developing a better understanding of the environmental and biological conditions that lead to larvae mortality events in hatcheries. We tested the virulence of 51 Vibrio strains towards Pacific Oyster (Crassostreae gigas) larvae and sequenced draft genomes of 42 hatchery-associated vibrios to determine groups of orthologous genes associated with virulence and to determine the phylogenetic relationships among pathogens and non-pathogens of C. gigas larvae. Results: V. coralliilyticus strains were the most prevalent pathogenic isolates. A phylogenetic logistic regression model identified over 500 protein-coding genes correlated with pathogenicity. Many of these genes had straightforward links to disease mechanisms, including predicted hemolysins, proteases, and multiple Type 3 Secretion System genes, while others appear to have possible indirect roles in pathogenesis and may be more important for general survival in the host environment. Multiple metabolism and nutrient acquisition genes were also identified to correlate with pathogenicity, highlighting specific features that may enable pathogen survival within C. gigas larvae. Conclusions: These findings have important implications on the range of pathogenic Vibrio spp. found in oysterrearing environments and the genetic determinants of virulence in these populations. Keywords: Vibrio, Aquaculture, Comparative genomics, Oyster larvae, Vibrio coralliilyticus, Vibriosis, Crassostrea gigas, Prokaryotic genomics
Background The Vibrio genus represents a group of microorganisms ubiquitous in temperate marine, freshwater, and estuarine environments [1–3]. Members of this genus are known to have roles as commensal or pathogenic members of marine animal microbiomes [4, 5], or as free-living members of the environment [6, 7]. Incidences of diseases attributed to Vibrio bacteria are * Correspondence: [email protected] 1 Department of Microbiology, Oregon State University, Corvallis, Oregon 97331, USA Full list of author information is available at the end of the article
broadly referred to as “vibriosis”, with the identities of the etiological agents and their pathogenic mechanisms varying between hosts. In aquaculture settings, vibriosis outbreaks can lead to large economic and productivity impacts [8]. Commercial shellfish hatcheries are impacted by disease outbreaks attributed to vibrios, which can result in large mass mortalities of larvae [9–12]. Genomic sequencing of marine pathogens has aided our understanding of the genetic mechanisms of viru
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