- Volume 50, Issue 2, 2000

Staircase electrophoresis (SCE) in polyacrylamide gels was used to analyse the stable low-molecular-weight (LMW) RNA profiles of several yeast species and genera. As in prokaryotes, this new electrophoretic technique results in good separation of molecules forming LMW RNA profiles in yeasts. In this study it is reported that, while LMW RNA profiles in prokaryotes include only 5S rRNA, and class 2 and class 1 tRNA, these profiles in eukaryotes also include 5.8S rRNA. Differences in the number and distribution of RNA bands in these profiles allowed identification of differences among the yeast species and genera assayed. LMW RNAs, analysed by SCE, provide a yeast fingerprint that allows them to be clearly differentiated and will in the future enable the rapid assignment of yeast isolates to already described species and the detection of new ones.

For species discrimination, DNA relatedness, nuclear DNA (nDNA) base compositions and internal transcribed spacer (ITS) regions were studied in strains of the 'washingtonensis group' consisting of the type strains of Tilletiopsis washingtonensis, Tilletiopsis cremea and Tilletiopsis lilacina as wells as nine strains previously identified as any one of the three species. T. washingtonensis is the neotype of the genus Tilletiopsis while T. cremea and T. lilacina are currently recognized as conspecific with T. washingtonensis. The G + C content of the DNA of the strains examined in this study was 66-68 mol%. The type strains of T. washingtonensis, T. cremea and T. lilacina were clearly discriminated on the basis of DNA complementarity. These genospecies should be treated as species. Moreover, an unrooted dendrogram constructed from ITS nucleotide sequences showed that the 'washingtonensis group' was divided into three clusters, corresponding to the three species T. washingtonensis, T. cremea and T. lilacina, respectively. The species descriptions of T. washingtonensis, T. cremea and T. lilacina are emended accordingly.

Unequivocal and rapid classification of yeast cultures cannot be accomplished exclusively on the basis of unstable phenotypic traits, but requires molecular tests relating to the whole genome (or the largest possible portion of it). DNA-DNA reassociation meets this requirement, although many procedures proposed for calculating overall sequence similarity are expensive and time-consuming, thus restricting the possibility of unequivocal classification to a few specialized laboratories. A novel method, based on non-radioactive dot-blot hybridization of whole genomic DNA, has shown high and reproducible proportionality between the detected signal and the amount of double-stranded DNA effectively present on the membrane. This procedure has been optimized to obtain, within two working days, DNA relatedness values between unknown cultures and the type strains of the species previously indicated by a few conventional tests. The effective ability of the method to discriminate strains belonging to different species has been tested within taxonomic models consisting of yeast type cultures already certified by spectrophotometric reassociation.

The taxonomic status of the type species of the genus Paenibacillus cannot be easily determined according to the rules of the Bacteriological Code since the rules may be interpreted in an ambiguous way. Depending upon how the rules are applied the type species may be either Paenibacillus polymyxa or Paenibacillus durus. In addition, depending upon the way in which the Bacteriological Code is interpreted, the question of whether the name P. durus (Collins et al. 1994) has been validly published must also be addressed.

We propose Salmonella paratyphi sp. nov., nom. rev., by raising Salmonella choleraesuis subsp. choleraesuis serovar Paratyphi A to species status and request an Opinion to include the specific epithet paratyphi in the binary combination of Salmonella paratyphi in the list of epitheta specifica conservanda.

In 1994, the Judicial Commission of the ICSB announced that Le Minor and Popoff's Request for an Opinion in 1987 to designate Salmonella enterica sp. nov., nom. rev. as the type and only species of the genus Salmonella was denied. Thus, the current species of the genus Salmonella are Salmonella typhimurium, Salmonella enteritidis, Salmonella typhi, Salmonella choleraesuis (including six subspecies) and Salmonella bongori, with the type species, S. choleraesuis (Smith 1894) Weldin 1927 (Approved Lists 1980). Because the decision of the Judicial Commission about the request by Le Minor in 1987 was suspended for 7 years, the non-validated name 'S. enterica' has been used among microbiologists and has caused confusion in the nomenclature of Salmonella. In order to overcome such confusion, and because of their importance as human pathogens, we herein propose to recognize the nomenclatural status of S. typhi, S. enteritidis and S. typhimurium as species and request to issue an Opinion to conserve the specific epithets enteritidis and typhimurium in the species names Salmonella enteritidis and Salmonella typhimurium.