Some ultrastructural features ofPlanctomyces bekefii,morphotype I of theBlastocaulis-Planctomyces group of budding and appendaged bacteria

The ultrastructure ofPlanctomyces bekefii, a budding and appendaged bacterium, has been examined using samples obtained directly from pond water, its natural habitat. The prokaryotic nature of this morphologically unusual microbe was verified by observations of thin sections. Its major appendage, the nonprosthecate stalk, is shown to have a tubular structure, with a substructure of hollow fibers. Some details of the budding process and other ultrastructural features are presented.