Description
Free-living from anaerobic or micro-aerophilic habitats, cells amoeboid reaching 3 mm long with a large, anterior pseudopod and a posterior uroid. With one to several nuclei . Short flagella have been demonstrated at some stages of the life cycle. Cytoplasm contains 2 to several "glycogen bodies" as large as the nuclei (1 0 IJm). A complex life cycle has been described . In spring , cysts release small binucleate amoebae , which grow and become multinucleate and acquire endosymbiotic bacteria . They become elongate with a posterior uroid, and flagella are evident at this stage . The cells later become spherical , and endosymbiotic bacteria congregate around the nuclei. These cells fragment into rosettes giving rise either to cysts in winter or to small amoebae which may undergo another cycle of development (Whatley and Chapman-Andresen, 1990} . Electron-microscopical studies have shown that the basal bodies and flagella are connected to a cone of microtubules . The microtubules are not in contact with the nuclei when the nuclei are surrounded by endosymbiotic bacteria. Three types of bacteria have been observed : one is a large , cylindrical bacterium with an internal cleft , the other is a long rod-shaped bacterium , the third is a methanogen (Stumm and Zwart , 11 00 PELOB 1986 ; Griffin , 1988 ; Whatley and Chapman- Andresen , 1990) . Many species have been assigned to this genus, but all may be assignable to the type species P. palustris Greeff, 1874. of mi crotubules (arrows) arising from the basal body (b) . These microtubules link the flagellum to the nucleus. Note the heli x- like structure around th axoneme of the flagellum (a rrowhead) and the large nucleolu s. Bar=1 ~m .
Type species
Figures
Raw text
Free-living from anaerobic or micro-aerophilic habitats, cells amoeboid reaching 3 mm long with a large, anterior pseudopod and a posterior uroid. With one to several nuclei . Short flagella have been demonstrated at some stages of the life cycle. Cytoplasm contains 2 to several "glycogen bodies" as large as the nuclei (1 0 IJm). A complex life cycle has been described . In spring , cysts release small binucleate amoebae , which grow and become multinucleate and acquire endosymbiotic bacteria . They become elongate with a posterior uroid, and flagella are evident at this stage . The cells later become spherical , and endosymbiotic bacteria congregate around the nuclei. These cells fragment into rosettes giving rise either to cysts in winter or to small amoebae which may undergo another cycle of development (Whatley and Chapman-Andresen, 1990} . Electron-microscopical studies have shown that the basal bodies and flagella are connected to a cone of microtubules . The microtubules are not in contact with the nuclei when the nuclei are surrounded by endosymbiotic bacteria. Three types of bacteria have been observed : one is a large , cylindrical bacterium with an internal cleft , the other is a long rod-shaped bacterium , the third is a methanogen (Stumm and Zwart , 11 00 PELOB 1986 ; Griffin , 1988 ; Whatley and Chapman- Andresen , 1990) . Many species have been assigned to this genus, but all may be assignable to the type species P. palustris Greeff, 1874. of mi crotubules (arrows) arising from the basal body (b) . These microtubules link the flagellum to the nucleus. Note the heli x- like structure around th axoneme of the flagellum (a rrowhead) and the large nucleolu s. Bar=1 ~m .