Deoxyribonucleic and Ribonucleic Acid Homology Studies of the Genera Azospirillum and Conglomeromonas

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Abstract
Ribosomal ribonucleic acid (RNA) homology studies indicated that there is 90 to 96% homology between Azospirillum lipoferum and Azospirillum brasilense and 64 to 70% homology between these two species and Azospirillum amazonense. These findings support the inclusion of these three species in the genus Azospirillum. In contrast, “Azospirillum seropedicae” strains showed very little homology with the other Azospirillum species (< 22% RNA homology) and should not be considered a member of this genus. The taxonomic placement of “Azospirillum seropedicae” is uncertain. The nearest relatives of the genus Azospirillum were Aquaspirillum itersonii and Rhodospirillum rubrum (>65% RNA homology); Gluconobacter oxydans and Beijerinckia indica exhibited 30 to 60% RNA homology with Azospirillum species. Deoxyribonucleic acid studies indicated that Conglomeromonas largomobilis subsp. largomobilis was related to Azospirillum lipoferum at a level of deoxyribonucleic acid homology of >45% and at a level of RNA homology of 99%; moreover, this organism was found to be a microaerophilic nitrogen fixer. Thus, C. largomobilis subsp. largomobilis is a subjective synonym of Azospirillum lipoferum. In contrast, deoxyribonucleic acid homology studies indicated that C. largomobilis subsp. parooensis is not related to C. largomobilis, Azospirillum lipoferum, or any other species tested, and its taxonomic position is uncertain. Several strains of azospirilla which form unique star-shaped colonies were identified as Azospirillum lipoferum by deoxyribonucleic acid homology.