# Mytilus galloprovincialis as a Natural Reservoir of Vibrio harveyi: Insights from GFP-Tagged Strain Tracking

## TL;DR

Mediterranean mussels can accumulate Vibrio harveyi in their tissues and waste, acting as a natural reservoir for this marine bacterium.

## Contribution

This study demonstrates that mussels can act as a reservoir for Vibrio harveyi through controlled experiments using a GFP-tagged strain.

## Key findings

- Mussels accumulated high levels of Vibrio harveyi in their digestive glands and biodeposits.
- Salinity had a greater impact on bacterial accumulation than temperature.
- Mussels showed immune responses like granulocytomas and hemocytic infiltrations when exposed to Vibrio harveyi.

## Abstract

Vibrios are widespread in marine environments, and their persistence is often linked to natural reservoirs such as filter-feeding bivalves. This study investigated the capacity of the Mediterranean mussel, Mytilus galloprovincialis, to act as a reservoir of Vibrio harveyi using a GFP-tagged strain in controlled experiments. Mussels (shell length 4–6 cm) were exposed to V. harveyi gfp in estuarine and seawater at 12 °C and 20 °C over six days. Bacterial accumulation in gills, digestive gland, and gonads, as well as in feces and pseudofeces, was quantified, and the immune response following microbial challenge was assessed by histopathological analysis. Mussels actively removed V. harveyi from the water, but not completely. Vibrios were rapidly accumulated in organs, with the highest densities in the digestive gland (up to 107–108 CFU g−1), and substantial bacterial loads detected in biodeposits (1.55–3.77 × 107 CFU g−1). Salinity had a greater effect than temperature on bacterial accumulation, with consistently higher counts in seawater assays. Concurrently with bacterial accumulation, mussels activated their immune system, as evidenced by the detection of granulocytomas and hemocytic infiltrations. Overall, these results demonstrate that M. galloprovincialis accumulates V. harveyi in tissues and biodeposits, serving as a natural reservoir for this bacterium.