CHEMOSENSORY BEHAVIOR OF STROMBIDIUM-PURPUREUM, AN ANAEROBIC OLIGOTRICH WITH ENDOSYMBIOTIC PURPLE NONSULFUR BACTERIA

Strombidium purpureum Kahl, is an anaerobic oligotrichous ciliate with endosymbiotic phototrophic bacteria. Like other anaerobic ciliates, S. purpureum reacts to O-2-pressure. In the light, the ciliates avoid even traces of O-2 (< 1% atmospheric saturation). In the dark, however, the ciliates accumulate in water with a pO(2) of 1-4% atmospheric saturation. Experiments show that ciliates which have accumulated in the dark under microaerophilic conditions react when the light is turned on, and their ability to escape is enhanced by steep O-2-gradients. The ciliates orient themselves in O-2-gradients by a series of phobic responses. They tumble whenever they swim towards a higher O-2-tension and thus they eventually all swim in the direction of lower pO(2). The ecological implications of such behaviour are discussed.