Polymorphic bacterial symbionts in the anaerobic ciliated protozoonMetopus

Abstract

Abstract In the anaerobic ciliate Metopus palaeformis , all endosymbionts are electron dense, rod-shaped bacteria. In Metopus contortus , rod-shaped symbionts co-exist with a variety of other morphological forms of the symbiont. The latter appear to represent stages in a changing morphology of the rods, a process which entails progressive stripping of the bacterial cell wall, as a prelude to attachment of the transformed symbiont to one or more hydrogensomes. In M. palaeformis , the morphology of the symbionts does not change and they do not become attached to the hydrogenosomes. All symbionts in both ciliate species show F 420 autofluorescence and inhibition by bromoethanesulfonic acid, so they are all, probably, methanogens.