Espada-Hinojosa Salvador, Drexel Judith, Kesting Julia, Kniha Edwin, Pifeas Iason, Schuster Lukas, Volland Jean-Marie, Zambalos Helena C, Bright Monika
Department of Functional and Evolutionary Ecology, University of Vienna, Vienna, Austria.
PLoS One. 2022 Feb 25;17(2):e0254910. doi: 10.1371/journal.pone.0254910. eCollection 2022.
The mutualism between the thioautotrophic bacterial ectosymbiont Candidatus Thiobius zoothamnicola and the giant ciliate Zoothamnium niveum thrives in a variety of shallow-water marine environments with highly fluctuating sulfide emissions. To persist over time, both partners must reproduce and ensure the transmission of symbionts before the sulfide stops, which enables carbon fixation of the symbiont and nourishment of the host. We experimentally investigated the response of this mutualism to depletion of sulfide. We found that colonies released some initially present but also newly produced macrozooids until death, but in fewer numbers than when exposed to sulfide. The symbionts on the colonies proliferated less without sulfide, and became larger and more rod-shaped than symbionts from freshly collected colonies that were exposed to sulfide and oxygen. The symbiotic monolayer was severely disturbed by growth of other microbes and loss of symbionts. We conclude that the response of both partners to the termination of sulfide emission was remarkably quick. The development and the release of swarmers continued until host died and thus this behavior contributed to the continuation of the association.
硫自养细菌外共生体“候选硫氏动物栖居菌”（Candidatus Thiobius zoothamnicola）与大型纤毛虫“雪白聚缩虫”（Zoothamnium niveum）之间的共生关系，在各种硫化物排放高度波动的浅水海洋环境中蓬勃发展。为了长期存续，双方都必须进行繁殖，并在硫化物停止排放之前确保共生体的传递，这使得共生体能够进行碳固定并为宿主提供养分。我们通过实验研究了这种共生关系对硫化物耗尽的反应。我们发现，群体在死亡前会释放一些最初存在的以及新产生的大型游动孢子，但数量比暴露于硫化物时要少。没有硫化物时，群体上的共生体增殖较少，并且与暴露于硫化物和氧气的新鲜采集群体中的共生体相比，变得更大且更呈杆状。共生单层受到其他微生物生长和共生体损失的严重干扰。我们得出结论，双方对硫化物排放终止的反应非常迅速。游动孢子的发育和释放一直持续到宿主死亡，因此这种行为有助于共生关系的延续。
