Experimental Induction of Heterotrophic to Autotrophic Conversion, Realized by the Enforced Primary Endosymbiosis of Photosynthetic Bacteria onto Eukaryotic Amoebae

Abstract

The primary endosymbiosis of cyanobacteria with primitive eukaryotes is assumed to have occurred in ancient times, leading to the formation of plants with chloroplasts. However, since this possibility has remained experimentally unproven, we tried to convert heterotrophic eukaryotes like protozoa to autotrophs with chloroplasts. For this, when eukaryotic and heterotrophic Dictyostelium cells were forcibly cultivated with two kinds of photosynthetic bacteria (the purple non-sulfur bacterium Rhodobacter and then the cyanobacterium Synechocystis ) as food sources, unique autotrophic organisms consisting of multinucleate plasmodia and their derived amoeboid cells, which had very strange morphology and behaviors, were formed by endosymbiosis of the bacteria. In this case, long-term pre-cultivation with Rdodobacter seemed to be prerequisites for the formation of the autotrophic organisms. The resulting, green-colored plasmodium contained a number of Synechocystis -derived bodies in the cytoplasm. The measurement of chlorophyll fluorescence indicates that the Synechocystis -derived bodies are like chloroplasts giving the ability of photosynthesis. Only, since the fine structural characteristics and genetic background of the autotrophic multinucleate plasmodia and their derived-amoeboid cells are extremely strange, we discuss the possibility of thinking about those reasons.