Summary auto-generated
This study determined the phylogenetic position of Anaerobacter polyendosporus, a Gram-positive anaerobic bacterium capable of forming multiple endospores per cell, by sequencing its 16S rRNA gene. Phylogenetic analysis using neighbor-joining methods placed A. polyendosporus within Clostridium cluster I, subcluster A, most closely related to Clostridium intestinale (94.8% sequence identity) and C. fallax (93.1%). Like other saccharolytic clostridia in this group, the bacterium ferments carbohydrates to produce butyric acid and other organic acids, possesses a Gram-positive cell wall, and forms endospores. However, A. polyendosporus exhibits distinctive phenotypic features not reflected in the modest genetic divergence: large cell size, polysporogenesis (up to seven spores per cell), alternative developmental pathways including formation of polygonal cells, and unusual cytoplasmic membrane ultrastructure with intramembrane lipid layers. The bacterium is phylogenetically distant from the other known polysporogenic bacterium, Metabacterium polyspora (79.9% identity), which differs in cell wall type, spore morphology, and ecological niche. Electron microscopy confirmed characteristic Clostridium spore ultrastructure including coats, exosporium, and membranes.
Key findings
- A. polyendosporus belongs to Clostridium cluster I, subcluster A, with C. intestinale as its closest phylogenetic relative at 94.8% 16S rRNA identity
- The bacterium exhibits significant phenotypic distinctiveness despite modest genetic divergence from related Clostridium species, including polysporogenesis up to seven spores per cell and unusual intramembrane lipid structures
- A. polyendosporus is distantly related to Metabacterium polyspora (79.9% identity) and differs in Gram-staining properties, spore morphology, and habitat
- The organism is a Gram-positive, anaerobic, saccharolytic bacterium that ferments carbohydrates to produce butyric acid and other organic acids
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Abstract
The almost complete sequence of the 16S rRNA gene of the Gram-positive polysporogenic bacterium Anaerobacter polyendosporus was determined. This allowed phylogenetic analysis of A. polyendosporus by comparing sequences of the 16S rRNA gene of this bacterium to similar genes of other Gram-positive bacteria. It was shown that this polysporogenic bacterium belongs to the Clostridium cluster I, subcluster A. Phylogenetically, A. polyendosporus is distantly related to another polysporogenic, but non-cultivatable, bacterium, Metabacterium polyspora and can be satisfactorily clustered within the saccharolytic 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 possesses such common phenotypic features as a Gram-positive cell wall structure, anaerobiosis, derivation of energy from carbohydrate fermentation yielding butyric acid among other organic acids and the capacity for endogenous spore-formation. However, the scale of evolutionary change in the 16S rRNA gene between A. polyendosporus and phylogenetically related Clostridium species does not correspond to the profound changes in the phenotype of A. polyendosporus. Distinctive phenotypic features of the latter are large cell size, polysporogenesis (up to seven spores per cell), alternative modes of development and an unusual membrane ultrastructure.