Phylogenetic status of Anaerobacter polyendosporus, an anaerobic, polysporogenic bacterium

The almost complete sequence of the 16S rRNA gene of the Gram-positive poly sporogenic bacterium Anaerobacter polyendosporus was determined. This allow ed phylogenetic analysis of A. polyendosporus by comparing sequences of the 16S rRNA gene of this bacterium to similar genes of other Gram-positive ba cteria. It was shown that this polysporogenic bacterium belongs to the Clos tridium cluster I, subcluster A. Phylogenetically, A. polyendosporus is dis tantly related to another polysporogenic, but non-cultivatable, bacterium, 'Metabacterium polyspora' and can be satisfactorily clustered within the sa ccharolytic clostridia with a low DNA G + C content grouped in subcluster A . A. polyendosporus was most closely related to Clostridium intestinale (94 .8 % identity of 16S rRNA genes) and Clostridium fallax (93.1%). Like other members of the Clostridium cluster I, subcluster A, A. polyendosporus poss esses such common phenotypic features as a Gram-positive cell wall structur e, anaerobiosis, derivation of energy from carbohydrate fermentation yieldi ng butyric acid among other organic acids and the capacity for endogenous s pore-formation. However, the scale of evolutionary change in the 16S rRNA g ene between A. polyendosporus and phylogenetically related Clostridium spec ies does not correspond to the profound changes in the phenotype of A. poly endosporus. Distinctive phenotypic features of the latter are large cell si ze, polysporogenesis (up to seven spores per cell), alternative modes of de velopment and an unusual membrane ultrastructure.