Life cycle and interactions in a thiotrophic symbiosis

The fascination of symbioses originates in the fact that, through association, two distinct organisms become a symbiotic entity - something considered completely new. The thiotrophic ectosymbiosis between a sessile colonial ciliate Zoothamnium niveum (Ciliophora, Oligohymenophora) and chemoautotrophic bacteria lives under extreme environmental conditions at mangrove peat walls in the Caribbean Sea that leak toxic hydrogen sulfide. The two bacterial morphotypes of the same phylotype coat the ciliate in a strict monolayer. They oxidize sulfide to gain energy for inorganic carbon fixation and nourish their host. The aims of this study are to investigate the survival, maintenance, and specificity of the Zoothamnium niveum symbiosis in situ and in vivo, using an automated flow-through respirometry system to simulate `natural conditions` and various `stress conditions. This study will include the documentation of the life cycle of the host and its growth and asexual reproduction rate, as well as the symbiont population density and symbiont specificity, its growth (total population analysis) and related physiological parameters (macromolecular composition, respiratory activity, autotrophic potential) throughout the host`s life cycle. For the first time we plan to combine classical microscopy, electron microscopy, various molecular biological methods, in situ and in vivo measurements, techniques tested reliable in other biological fields. With the advantage of being able to cultivate the Zoothamniu niveum symbiosis for a few successive generations, we will be able to use this model system to estimate the range of chemical tolerance of both partners and to gain insight into the dynamics and interactions between host and ectosymbionts. Furthermore, these descriptive data will be used to develop hypothesis an the origin and evolution of thiotrophic symbioses and Gould lead the way for investigations of other chemoautotrophic symbioses.