Phase-contrast light microscopy revealed that only one of eight cultivated strains belonging to the group of sheathed bacteria actually produced a sheath in standard growth media. Two strains produced branched cells, but other morphological characteristics that were used to identify these bacteria were consistent with previously published descriptions. Genomic fingerprints, which were obtained by performing PCR amplification with primers corresponding to enterobacterial repetitive intergenic consensus sequences, were useful for distinguishing between the genera and , as well as among individual strains. The complete 16S ribosomal DNA (rDNA) sequences of two strains of “ (strains SP-6 and SS-1) were determined. In addition, partial sequences (approximately 300 nucleotides) of one strain of (strain LMG 7171), an unidentified strain (strain NC-1), and four strains of (strains ATCC 13338 [T = type strain], ATCC 15291, ATCC 29329, and ATCC 29330) were determined. We found that two of the strains (ATCC 15291 and ATCC 13338), which differed in morphology and in their genomic fingerprints, had identical sequences in the 300-nucleotide region sequenced. Both parsimony and distance matrix methods were used to infer the evolutionary relationships of the eight strains in a comparison of the 16S rDNA sequences of these organisms with 16S rDNA sequences obtained from ribosomal sequence databases. All of the strains clustered in the subdivision of the β subclass of the , which confirmed previously published conclusions concerning selected individual strains. Additional analyses revealed that all of the strains clustered in one closely related group, while the strains clustered in two separate lineages that were approximately equidistant from the cluster. This finding suggests that the tentative species “ needs to be more clearly defined and compared with other species belonging to the genus


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