The control of extracellular bacterial symbionts in thyasirid bivalves

在动物的一生中，它们不断地与细菌相互作用。虽然其中一些细菌是致病的病原体，但许多其他细菌是无害的，甚至是有益的。有些细菌甚至对与之互动的动物的营养、发育或免疫系统至关重要；例如，居住在我们消化道中的许多细菌对我们的健康和福祉至关重要。我们对动物和有益细菌之间发生的复杂相互作用知之甚少：例如，如此截然不同的生物体是如何找到彼此并保持良好的长期关系的？我的研究重点是动物和有益细菌如何相互作用，合作和交换资源。为了研究这个问题，我使用了一个独特的模型系统：一群被称为thyasiids的小型冷水蛤，它们在加拿大许多港口、峡湾和近海地点的含硫沉积物中挖洞。袋狸被认为是生态系统工程师，因为它们的挖洞活动有助于从沉积物中去除硫（这对大多数动物都是有毒的）。袋虫的鳃内有大量以硫为能量来源的细菌（“共生体”）。袋狸纲动物用可伸展的脚在沉积物中挖洞，为它们的共生体提供硫，这种行为被称为硫开采；反过来，共生体作为蛤蜊的补充食物来源。硫化物开采改变了洞穴周围沉积物的化学成分。我之前对共生囊虫的研究表明，在操纵环境条件和监测它们的行为的同时，将这些蛤长期饲养在水族箱中是可能的。我和我的学生将进行类似的实验，结合对宿主组织的详细观察（例如，使用高倍显微镜来可视化和量化细菌，或荧光标记来跟踪细胞过程，如细胞分裂或细胞死亡），以了解对维持囊虫共生功能至关重要的因素。我们还将使用基因组方法来深入了解参与宿主相互作用的潜在共生体基因，并研究thyasirid共生体的自由生活形式，看看它们是否被宿主蛤的洞穴内壁所吸引。这项研究对于理解所有动物如何与有益细菌相互作用很重要；特别是，它有望为宿主行为对维持共生关系的重要性提供新的见解。此外，这项工作将有助于我们更好地描述袋虫在加拿大水域的生态作用；这些知识是及时的，因为我们沿海水域的沉积物由于有机物负荷而正在经历越来越多的硫富集程度，而共生的袋虫可以很容易地定殖并修复这些受影响的沉积物

Throughout their lives, animals constantly interact with bacteria. While some of these bacteria are disease-causing pathogens, many others are harmless or even beneficial. Some bacteria can even be fundamentally important for the nutrition, development or immune system of the animals with which they interact; for example, many of the bacteria dwelling in our digestive tracts are crucial to our health and well being. We know very little about the complex interactions that take place between animals and beneficial bacteria: for example, how do such dramatically different organisms find each other and maintain good, long-term relationships? My research focuses on how animals and beneficial bacteria interact, cooperate and exchange resources. To study this, I use a unique model system: a group of small, cold-water clams called thyasirids that burrow in sulfur-containing sediments in many harbours, fjords, and offshore sites around Canada. Thyasirids are considered to be ecosystem engineers because their burrowing activities help to remove sulfur (which is toxic to most animals) from sediments. The gills of thyasirids harbour large populations of bacteria ("symbionts") that use sulfur as an energy source. Thyasirids provide their symbionts with sulfur by burrowing in sediments using their extensible foot, a behaviour called sulfur mining; in turn, symbionts serve as a supplementary food source for the clams. Thyasirid sulfur mining changes the chemistry of sediments around burrows. My previous research on symbiotic thyasirids has shown that it is possible to keep these clams for long periods of time in aquaria while manipulating environmental conditions and monitoring their behaviours. My students and I will perform similar experiments, in combination with detailed observations of host tissues (e.g. using high magnification microscopes to visualize and quantify bacteria, or fluorescent markers to track cellular processes such as cell division or cell death), to understand the factors that are important for maintaining a functioning symbiosis in thyasirids. We will also use genomic approaches to gain insights on potential symbiont genes involved in host interactions, and study the free-living form of thyasirid symbionts to see if they are attracted to the burrow linings of their host clams.***This research is important for understanding how all animals interact with beneficial bacteria; in particular, it is expected to provide novel insights on the importance of host behaviours for maintaining symbiotic relationships. In addition, this work will help us better characterize the ecological role of thyasirids in Canadian waters; such knowledge is timely given that sediments in our coastal waters are experiencing an increasing degree of sulfur enrichment as a result of organic matter loading, and symbiotic thyasirids could readily colonize and remediate these impacted sediments.**