Endosymbiotic methanogenic bacteria of the sapropelic amoebaMastigella

Large numbers of Gram-positive methanogenic bacteria, which morphologicallt resembled Methanobacterium formicicum, were found in the flagellated amoeba Mastigella from fresh water sapropel. A non-methanogenic Gram-positive bacterium with a characteristic axial cleft was found to live in close association with the amoebal nucleus. The similarity between the symbiotic system of Mastigella and that of the giant amoeba Pelomyxa is discussed, as well as the contribution of sapropelic amoebae to the methanogenesis of the sapropel ecosystem.