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The phylogenetic position of an acidophilic chemo-organotrophic menaquinone-containing bacterium, Acidobacterium capsulatum, was studied on the basis of 16S rRNA gene sequence information. A. capsulatum showed the highest level of sequence similarity to Heliobacterium chlorum, a member of the Gram-positive group, yet this level was only 81%. Distance matrix tree analysis suggested that A. capsulatum belongs to a unique lineage deeply branching from the Chlamydia-Planctomyces group or from the Gram-positive line.
Hiraishi et al. (Sun,) studied this question.