title: Green paramecia as an evolutionary winner of oxidative symbiosis: a hypothesis and supportive data.
abstract: A single cell of the green paramecia (Paramecium bursaria) harbors several hundreds of endo-symbiotic Chlorella-like algae in its cytoplasm. Removal of algae from the host organism and re-association of ex-symbiotic host paramecia with ex-symbiotic algae can be experimentally demonstrated in the laboratory. However, the mechanism precisely governing the alga-protozoan association is not fully understood, and the origin of symbiosis in the evolutionary view has not been given. Here, we propose the possible biochemical models (models 1 and 2) explaining the co-evolution between Paramecium species and algal symbionts by pointing out that algal photosynthesis in the host paramecia plays a dual role providing the energy source and the risk of oxidative damage to the host. Model 1 lays stress on the correlation between the (re)greening ability of the paramecia and the tolerance to oxidative stress whereas model 2 emphasizes the cause of evolutionary selection leading to the emergence of Paramecium species tolerant against reactive oxygen species.
authors.affiliation: Graduate School of Environmental Engineering, The University of Kitakyushu, Kitakyushu 808-0135, Japan. kawanotom@env.kitakyu-u.ac.jp
authors.forename: Tomonori
authors.initials: T
authors.lastname: Kawano
authors.forename: Takashi
authors.initials: T
authors.lastname: Kadono
authors.forename: Toshikazu
authors.initials: T
authors.lastname: Kosaka
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Hosoya
mesh_terms: D000818:Animals; D002708:Chlorella / Q000502:physiology; D008954:Models, Biological; D010084:Oxidation-Reduction; D010247:Paramecium / Q000145:classification / Q000235:genetics*; D010788:Photosynthesis / Q000502:physiology*; D017382:Reactive Oxygen Species / Q000378:metabolism*; D013559:Symbiosis / Q000502:physiology*
chemical_list: D017382:Reactive Oxygen Species