ENDOSYMBIOTIC PURPLE NONSULFUR BACTERIA IN AN ANAEROBIC CILIATED PROTOZOAN

The marine ciliate Strombidium purpureum Kahl harbours endosymbiotic purple non-sulphur bacteria. The bacteria contain bacteriochlorophyll a and the carotenoid spirilloxanthin, and they have photosynthetic membranes and cell walls. The ciliates require light for survival and growth under anaerobic conditions; in the dark the cells prefer microaerobic conditions. The ciliates show a photosensory behaviour, and they accumulate in light at wave lengths corresponding to the absorption spectrum of the symbionts. The findings are discussed in terms of theories on the endosymbiotic origin of mitochondria.