A comprehensive study of the intra- and intergeneric relationships of species in which we used DNA-rRNA hybridization is described. Radioactively labeled rRNAs from biovar bengal, , and several other organisms were hybridized with filter-fixed DNAs from representative strains of the genus and many other possibly related genera of gram-negative bacteria. Our results show that the genus is very heterogeneous and should be restricted to , the type species, including biovar serpens and biovar bengal. DNA-DNA hybridization data showed that biovar bengal exhibits only 55 to 60% binding with biovar serpens strains. , the only rod-shaped organism of the genus, is the only other species located on the 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 species, is a member of a different genus, for which we propose the name gen. nov., comb. nov. , and should also be removed from the genus 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 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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