Comparative genomic analysis of Vibrios yields insights into genes associated with virulence towards C. gigas larvae

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 sp. found in oyster-rearing environments and the genetic determinants of virulence in these populations.

Comparison of Vibrio coralliilyticus virulence in Pacific oyster larvae and corals

“…Other studies using Drosophila (fruit flies) and Artemia (brine shrimp) applied the molecular postulates and assessed ΔvcpA mutants [8], but the results were inconclusive due to the presence of other VcpA-like proteases that may have complementary functions [26]. It has been predicted that V. coralliilyticus possess a plethora of potential virulence factors [7][8][9]27], but is it unclear whether specific sets of factors are reserved for the infection of certain hosts. This ambiguity highlights the need for more comprehensive studies using multiple strains across different hosts, which would benefit from application of the molecular postulates.…”

The pan‐genome of Splendidus clade species in the familyVibrionaceae: Insights into evolution, adaptation, and pathogenicity

“…Meanwhile, most species in the Splendidus clade had shown an association with pathogenicity (Table 1), particularly marine animals cultured in hatcheries, which has led to huge losses in the aquaculture industry (Dubert et al, 2017). Recently, genomic sequencing of these pathogens has provided us with insights into the genetic mechanisms of virulence in some of these systems (Kehlet‐Delgado et al, 2020). For example, according to the comparative genomic analysis of strains of V. toranzoniae , differential features of iron acquisition systems and capsule synthesis genes were the main reason that could explain the differences in the pathogenicity in fish (Lasa et al, 2017).…”

“…The ecologically and genetically diverse populations of V. splendidus may serve as useful models to study their environmental adaptations (Hunt et al, 2008; Le Roux et al, 2009). In addition, V. splendidus has become known as an opportunistic pathogen associated with various incidents of marine invertebrate mortalities, particularly in the Pacific Oyster Crassostrea gigas (Kehlet‐Delgado et al, 2020; Liang et al, 2022; Oyanedel et al, 2020).…”