External pH modulation during the growth of Vibrio tapetis , the etiological agent of Brown Ring Disease

Aims
Brown Ring Disease (BRD) is an infection of the Manila clam Ruditapes philippinarum due to the pathogen Vibrio tapetis . During BRD, clams are facing immunodepression and shell biomineralization alteration. In this paper, we studied the role of pH on the growth of the pathogen and formulated hypothesis on the establishment of BRD by V. tapetis .

Methods and Results
In this study, we monitored the evolution of pH during the growth of V. tapetis in a range of pH and temperatures. We also measured the pH of Manila clam hemolymph and extrapallial fluids during infection by V. tapetis . We highlighted that V. tapetis modulates the external pH during its growth, to a value of 7.70. During the development of BRD, V. tapetis also influences extrapallial fluids and hemolymph pH in vitro in the first hours of exposure and in vivo after 3 days of infection.

Conclusions
Our experiments have shown a close interaction between V. tapetis CECT4600, a pathogen of Manila clam that induces BRD, and the pH of different compartments of the animals during infection. These results indicate that that the bacterium, through a direct mechanism or as a consequence of physiological changes encountered in the animal during infection, is able to interfere with the pH of Manila clam fluids. This pH modification might promote the infection process or at least create an imbalance within the animal, that would favor its persistence. This last hypothesis should be tested in future experiment.

Significance and Impact of Study
This study is the first observation of pH modifications in the context of BRD and might orient future research on the fine mechanisms of pH modulation associated to BRD.

Rahmani A., Mathien C., Bidault A., Le Goïc N., Paillard C. and Pichereau V., in press. External pH modulation during the growth of Vibrio tapetis , the etiological agent of Brown Ring Disease. Journal of Applied Microbiology. Article (subscription required).


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