Physiological Characterization of Cyanophora paradoxa, a Flagellate Containing Cyanelles in Endosymbiosis

Abstract

Culture conditions are described under which Cyanophora paradoxa grows with a generation time of less than two days. The organism is an obligate photoautotrophic flagellate unable to degrade exogenous carbohydrates via respiration. It does not synthesize nitrogenase but can form a hydrogenase with similar properties as in blue-green algae. The photosynthetic O 2 -evolution pro­ceeds with essentially the same rate as in green or blue-green algae. Besides CO 2 , p-benzochinon, nitrate and nitrite also stimulate the photosynthetic O 2 -evolution. Nitrite reduction is strictly light- dependent where the stoicheiometry between nitrite-disappearance and photosynthetic O 2 -evolution is 1:1.5. It is concluded that the cyanelles supply the eucaryotic host both with carbon and nitrogen compounds.