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 s pecies and one Selenomonas species were cloned after PCR amplification. The results of PCR amplification showed that these species had two types of sp acer 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 h igh level of homology, Homology was particularly high for bacteria belongin g 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 o f that which had been previously reported for other bacteria. The results o f spacer homology analysis and the order of the tRNA genes suggest that the taxonomic classification of anaerobic bacteria isolated from the brewing p rocess should be re-examined.