COMPARISON OF THE SMALL 16S TO 23S INTERGENIC SPACER REGION (ISR) OF THE RIBOSOMAL-RNA OPERONS OF SOME ESCHERICHIA-COLI STRAINS OF THE ECORCOLLECTION AND ESCHERICHIA-COLI K-12

Several 16S to 23S spacers of 354 bp have been sequenced from six Esch erichia coli strains belonging to the ECOR collection, Four phylogenet ically informative variable sites were identified. The results of thei r comparison confirm the existence of two major phylogenetic branches in this species, as previously reported. Remarkable intercistronic het erogeneity was found in strain ECOR35 and its closest relatives, in wh ich at least one of the operons has suffered a major mutagenic event o r has an independent phylogenetic origin.