Comparative transcriptomic analysis of surf clams (Paphia undulate) infected with two strains of Vibrio spp. reveals the identity of key immune genes involved in host defense

Mingjia Yu,Yang Zhang,Xiaobo Wang,Lin Zheng,Minfu Wu,Ming Qi,Wandong Fu

doi:10.1186/s12864-019-6351-4

Abstract

BackgroundVibrio spp. is the major infection-producing marine bacteria in commercially important bivalve Paphia undulata. The host resistance is the major determining factor for the development of pathogenesis. To explore defense mechanisms, researchers have focused primarily on the study of differential expression of individual or specific groups of host immune genes during pathogen-challenge.ResultsWe compared the expression profile in the surf clams infected with avirulent V. alginolyticus and virulent V. parahaemolyticus to mark the possible molecular mechanisms of pathogenesis. Comparison of the differentially expressed genes between the two groups of Vibrio-infected clams revealed that the number of down-regulate genes in V. parahaemolyticus injected clams (1433) were significantly higher than the other group (169). Based on Gene Ontology classification, a large proportion of these down-regulate genes were found to be associated with cellular and molecular mechanisms for pathogen recognition, and immunity development thereby explaining the low survival rate for the V. parahaemolyticus-treated clams and suggesting a higher virulence of this bacterium towards the surf clams. Quantitative real-time PCR of 24 candidate genes related to immunity involving the JAK-STAT signaling pathway, complementary cascade, cytokine signaling pathway, oxidative stress, phagocytosis and apoptosis down regulated under V. parahaemolyticus infection, indicating compromised host defense. Furthermore, we could demonstrate a central role of JAK-STAT pathway in bacterial clearance. dsRNA mediated depletion of a clam STAT homolog gene results in dramatic increase in the infection by V. alginolyticus, a mildly pathogenic strain under control conditions.ConclusionsThe difference in gene expression profiles in surf clams treated with two Vibrio species with a differential pathogenicity to P. undulate and downstream molecular analysis could enlighten on the probable molecular mechanisms of the Vibrio pathogenesis and the virulence of V. parahaemolyticus in surf clams, which also benefits to develop new strategies for disease control in surf calm aquaculture.

Highlights

Vibrio spp. is the major infection-producing marine bacteria in commercially important bivalve Paphia undulata
V. parahaemolyticus is pathogenic towards P. undulata To test the pathogenicity of the two Vibrio species, V. parahaemolyticus and V. alginolyticus towards surf clam Paphia undulate, the survival rate of the infected clams were measures at 24 h, 36 h, 48 h, 60 h and 72 h postinjection
A clear difference in the survivality was observed between clams infected with V. parahaemolyticus (VP) and the ones infected with V. alginolyticus (VA) in comparison to the controls (C) (Fig. 1)

Summary

Introduction

Vibrio spp. is the major infection-producing marine bacteria in commercially important bivalve Paphia undulata. Bivalves are one of the earliest yet ubiquitous group of aquatic invertebrates with an estimated 10,000–20,000 living species. They are both economically and ecologically important with respect to food source, biomass and effects on communities. The sedentary and filter-feeding habits among the bivalve mollusks lead to the accumulation of microorganisms (bacteria, fungi and parasites). These microorganisms besides being the source of nourishment lead to the development of immune challenge in the mollusks [3]

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Discussion

Conclusion