First evidence for a Vibrio strain pathogenic to Mytilus edulis altering hemocyte immune capacities

Area of Science:

• Marine microbiology
• Invertebrate immunology
• Bacterial pathogenesis

Background:

• Mytilus edulis (blue mussel) aquaculture faces significant losses due to bacterial infections.
• Vibrio species are common pathogens affecting marine bivalves, but mechanisms of virulence and host immune evasion are not fully understood.

Purpose of the Study:

• To investigate the differential effects of virulent and innocuous Vibrio strains on Mytilus edulis hemocyte immune responses.
• To elucidate bacterial strategies for evading host immune defenses in marine invertebrates.

Main Methods:

• Isolation and characterization of virulent (10/068 1T1) and innocuous (12/056 M24T1) Vibrio isolates from Mytilus edulis.
• GFP-tagging of bacterial strains for live-cell imaging and infection studies.
• Assessment of hemocyte motility, phagocytosis, and oxidative burst (ROS production) in response to bacterial challenge and extracellular products (ECPs).

Main Results:

• The virulent strain 10/068 1T1 induced transient hemocyte motility enhancement followed by a significant decrease, while the innocuous strain 12/056 M24T1 increased hemocyte velocity.
• Strain 10/068 1T1 exhibited higher hemocyte invasion rates and its ECPs significantly inhibited phagocytosis and oxidative burst.
• Conversely, strain 12/056 M24T1 and its ECPs enhanced ROS production, indicating a lack of immune suppression.

Conclusions:

• The virulent Vibrio strain 10/068 1T1 possesses mechanisms to suppress key mussel immune functions, including phagocytosis and oxidative burst.
• Pathogenic Vibrio strains may evade host immune responses by actively altering hemocyte behavior and function, contributing to disease outbreaks in Mytilus edulis.