Taxonomic Note: A Pragmatic Approach to the Nomenclature of Phenotypically Similar Genomic Groups

Abstract

Occasionally, genomic groups (DNA groups, genomic species) that have been delimited by DNA-DNA pairing may be phenotypically so similar that they cannot be differentiated for the time being. In these situations it seems best to allow a nomenspecies to contain more than one genomic group and to refer to genomic groups of a nomenspecies as genomovars.

Ureibacillus gen. nov., a new genus to accommodate Bacillus thermosphaericus (Andersson et al. 1995), emendation of Ureibacillus thermosphaericus and description of Ureibacillus terrenus sp. nov.

“…The DNA GjC content of Bacillus thermosphaericus DSM 10633 T , determined by the thermal denaturation method, agrees with that obtained by HPLC (Andersson et al, 1995). Isolate TH29A showed a GjC value about 3n5 mol % higher, but a difference in thermal stability greater than 2 % is now considered a more realistic standard to delimit bacterial species (Ursing et al, 1995). This less strict definition seems to be particularly sound for the two strains in question, which were closely related either phylogenetically or genetically and phenotypically.…”

Occurrence of Multiple Genomovars of Burkholderia cepacia in Cystic Fibrosis Patients and Proposal of Burkholderia multivorans sp. nov.

“…Several other strains (including B. cepacia genomovars I and I1 and B. vietnamiensis strains) were reported to share more than 98% of their 16s rRNA sequences. This is obviously not a unique situation: biochemically similar groups with more than 98% 16s rRNA sequence similarity and a low level of DNA-DNA hybridization are present in many genera and are considered different species if sufficient differential phenotypic characteristics are available (29,36,41). However, the genomes of B. cepacia and related species (including B. glumae, R. pickettii, R. eutropha, R. solanacearum, and B. glathei) are unusual because of their organization in multiple (two to four) chromosomes or replicons.…”

“…In the absence of differential classical phenotypic tests, members of this B. cepacia complex were previously referred to as genomovar I (clusters i and v), genomovar I1 (cluster x), genomovar I11 (clusters xi and xii), genomovar IV (cluster vi), and B. vietnamiensis (clusters vii and viii) (13,37) in accordance with the guidelines and recommendations for the delineation of new species (36,41). These five major genomic groups (including B. vietnarniensis) correspond to five distinct species, each with a similar DNA base ratio of approximately 68 mol% (Table 3).…”

“…The term genomovar was recently introduced to denote phenotypically similar but genotypically distinct groups of strains that were previously referred to by a variety of different terms including genomic species, genomic groups, genospecies, or genomospecies (36). These genomovars share a low level of DNA hybridization and therefore represent distinct species for which an official binomial name is not proposed pending the availability of differential diagnostic tests.…”

Burkholderia cepacia genomovar VI, a new member of the Burkholderia cepacia complex isolated from cystic fibrosis patients.

“…As can be seen in According to the guidelines proposed by Ursing et al (1995), this new genomic species should be named B. multivorans genomovar II, pending the availability of differential diagnostic tests (Wayne et al, 1987 ;Ursing et al, 1995). However, since B. multivorans was originally known as B. cepacia genomovar II, the name B. multivorans genomovar II would cause significant confusion.…”