16S-23S rDNA spacer of Pectinatus, Selenomonas and Zymophilus reveal new phylogenetic relationships between these genera.

The 16S-23S rDNA spacer regions of two Pectinatus species, two Zymophilus species and one Selenomonas species were cloned after PCR amplification. The results of PCR amplification showed that these species had two types of spacer regions which differ in molecular size (long and short). Only the long spacer regions in these bacteria contained one or two tRNA genes (alanine and/or isoleucine). The spacer regions in these bacteria had a relatively high level of homology. Homology was particularly high for bacteria belonging to the same genus. Interestingly, the order of the two tRNA genes present in the long spacer regions of Pectinatus and Selenomonas was the reverse of that which had been previously reported for other bacteria. The results of spacer homology analysis and the order of the tRNA genes suggest that the taxonomic classification of anaerobic bacteria isolated from the brewing process should be re-examined.