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Intra- and Intergeneric Relationships of the Genus Aquaspirillum: Prolinoborus, a New Genus for Aquaspirillum fasciculus, with the Species Prolinoborus fasciculus comb. nov.

Laboratorium voor Microbiologie en microbiële Genetica, Rijksuniversiteit Gent, K. L. Ledeganckstraat 35, B-9000 Ghent, Belgium

^* Corresponding author.

ABSTRACT

A comprehensive study of the intra- and intergeneric relationships of Aquaspirillum species in which we used DNA-rRNA hybridization is described. Radioactively labeled rRNAs from Aquaspirillum anulus, A. serpens biovar bengal, A. delicatum, A. gracile, A. metamorphum, A. sinuosum, and several other organisms were hybridized with filter-fixed DNAs from representative strains of the genus Aquaspirillum and many other possibly related genera of gram-negative bacteria. Our results show that the genus Aquaspirillum is very heterogeneous and should be restricted to A. serpens, the type species, including A. serpens biovar serpens and A. serpens biovar bengal. DNA-DNA hybridization data showed that A. serpens biovar bengal exhibits only 55 to 60% binding with A. serpens biovar serpens strains. A. fasciculus, the only rod-shaped organism of the genus, is the only other Aquaspirillum species located on the A. serpens rRNA branch. With differences in the midpoint temperatures of thermal denaturation curves of the DNA-rRNA hybrids of more than 6°C, differences in genomic DNA G+C contents of 11 to 16 mol%, and a phenotype which differs from the phenotypes of all other Aquaspirillum species, A. fasciculus is a member of a different genus, for which we propose the name Prolinoborus fasciculus gen. nov., comb. nov. A. anulus, A. aquaticum, A. autotrophicum, A. delicatum, A. dispar, A. giesbergeri, A. gracile, A. itersonii, A. metamorphum, A. peregrinum, A. polymorphum, A. psychrophilum, A. putridiconchylium, and A. sinuosum should also be removed from the genus Aquaspirillum on the basis of phylogenetic data; these organisms form at least 10 distinct groups that are intermingled phylogenetically with the gram-negative bacteria belonging to rRNA superfamilies III and IV. Although DNA-rRNA hybridization results clearly reveal that the genus Aquaspirillum is a very heterogeneous taxon, no phenotypic information is available to differentiate the various phylogenetic branches of the aquaspirilia. Moreover, most of the species descriptions were based on only one or a few strains. Therefore, we will not propose nomenclatural changes until (i) sufficient readily determinable phenotypic characteristics are available and (ii) more strains have been isolated and investigated.

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				J.-H. Yoon, S.-J. Kang, S. Park, S.-Y. Lee, and T.-K. Oh Reclassification of Aquaspirillum itersonii and Aquaspirillum peregrinum as Novispirillum itersonii gen. nov., comb. nov. and Insolitispirillum peregrinum gen. nov., comb. nov. Int J Syst Evol Microbiol, December 1, 2007; 57(12): 2830 - 2835. [Abstract] [Full Text] [PDF]