Univ Brest, CNRS, IRD, Ifremer, UMR 6539 LEMAR, Plouzané, France.
J Appl Microbiol. 2020 Jul;129(1):3-16. doi: 10.1111/jam.14699. Epub 2020 Jun 14.
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.
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 haemolymph and extrapallial fluids (EPFs) 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 EPFs and haemolymph pH in vitro in the first hours of exposure and in vivo after 3 days of infection.
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 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 favour its persistence. This last hypothesis should be tested in future experiment.
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 with BRD.
棕环病（BRD）是菲律宾蛤仔（Ruditapes philippinarum）感染病原菌鳗弧菌（Vibrio tapetis）引起的疾病。在 BRD 期间，蛤仔面临免疫抑制和贝壳生物矿化改变。在本文中，我们研究了 pH 值对病原体生长的影响，并提出了鳗弧菌引起 BRD 的假说。
在本研究中，我们监测了在一系列 pH 值和温度下鳗弧菌生长过程中 pH 值的变化。我们还测量了感染鳗弧菌时菲律宾蛤仔血淋巴和外套膜外液（EPF）的 pH 值。我们发现鳗弧菌在生长过程中调节外部 pH 值，使其达到 7.70。在 BRD 发展过程中，鳗弧菌在暴露的最初几个小时内在体外和感染后 3 天内在体内也会影响 EPF 和血淋巴 pH 值。
我们的实验表明，BRD 的病原体菲律宾蛤仔鳗弧菌 CECT4600 与感染过程中动物不同部位的 pH 值之间存在密切相互作用。这些结果表明，细菌通过直接机制或由于感染过程中动物遇到的生理变化，能够干扰马尼拉蛤仔体液的 pH 值。这种 pH 值的改变可能会促进感染过程，或者至少会在动物体内造成失衡，从而有利于其持续存在。这个最后一个假设应该在未来的实验中进行检验。
本研究首次观察到 BRD 背景下的 pH 值改变，可能为未来与 BRD 相关的 pH 值调节精细机制的研究提供方向。
