Bio@Noon – Where oxygen is not popular (Anaerobic ciliates as a model group for studying the biodiversity and symbioses in anoxic environments)
Beinart Lab, Coastal Institute, Graduate School of Oceanography, University of Rhode Island
Complex life on Earth, largely dependent on utilizing oxygen for energy production, is currently undergoing an apparent decline of biodiversity of mass measurements and globally accelerating environmental changes. Recent studies showed that oxygen depleted areas in the ocean are increasing in number, extent and persistence, forming so called ‘dead zones’. Yet, diverse life forms thrive in these seemingly hostile conditions. Organisms that have adapted to permanent low oxygen concentrations range from prokaryotes, through diverse lineages of microbial eukaryotes, to complex metazoans. Although it is crucial to study adaptations to rapid environmental changes in anaerobes, our knowledge on anaerobic eukaryotes is critically scarce. Ciliates, one of the most diverse groups of unicellular eukaryotes, may represent an excellent model group to study adaptations to life in anoxia, as anaerobiosis has, to a varying degree, evolved in numerous lineages and provides a spectre of the evolutionary adaptations. Nevertheless, their evolution has only recently started gaining attention. The discovery of two new obligately anaerobic ciliate classes and the expansion of the known diversity of free-living anaerobic ciliates during the last ten years have sparked our curiosity in the obvious proclivity of ciliates to anaerobiosis. Could their well-known ability to establish symbiotic relationships with anaerobic archaea and bacteria play a role? To seek the answer, we have cultivated hundreds of anaerobic ciliates maintaining their intracellular archaeal and ectobiotic bacterial symbionts, studied their nature and relationships using light microscopic and molecular methods. Comparative genomic and transcriptomic analyses of several chosen candidates have provided us insights into the evolution of their transition to obligate anaerobiosis while maintaining complex mitochondrial energetic metabolism satisfactory for the large active cells.