One of the genes encoding the 5S ribosomal ribonucleic acid (rRNA) for the Leptospira biflexa strain Patoc I was isolated and sequenced. The physical maps of the 5S rRNA genes in Leptospira were constructed. The strains of Leptospira biflexa had two genes on their chromosome; these two 5S rRNA genes were located several kb apart and sequences flanking these genes were divergent. In contrast to saprophytic leptospires, maps in parasitic leptospires that had only one gene for 5S rRNA on their genome were highly conserved and the physical maps of the genes in almost all strains were similar.

The genomic DNA fragment which contains ribosomal RNA (rRNA) genes for Treponema phagedenis was cloned into bacteriophage vector lambda EMBL3. A restriction map of the fragment was constructed and the organization of the rRNA genes was determined. The fragment contained at least one copy of the 16S, 23S and 5S sequences and the genes are arranged in the order 16S-23S-5S. Southern hybridization using radiolabeled rRNA gene probes to genomic DNA from T. phagedenis strain Reiter and T. pallidum strain Nichols showed that these organisms have two radioactive fragments which hybridize to the probes in their genome. These results suggest that both pathogenic and non-pathogenic strains of Treponema may carry at least two sets of rRNA genes on their chromosomes.

A 16S ribosomal RNA gene from Leptospira interrogans serovar canicola has been cloned and sequenced. We have reported previously the physical organization of the rRNA genes in the organism (1) and the primary structure of a gene coding for the 23S rRNA (2). Here we present the primary structure of 16S rRNA gene. Various DNA fragments were obtained and subcloned into pUC 18. Deletion mutants were made by using a deletion kit (3). The DNA sequencing was performed on both strands by employing M13/dideoxy method (4). A more detailed analysis of secondary structure and phylogenetic implications will be presented elsewhere.

We determined the linkage of 16S, 23S, and 5S rRNA genes in several strains of Leptospira and Leptonema by DNA-DNA hybridization. Almost all the hybridizations in all leptospires used in these experiments gave two radioactive bands and the results strongly suggest that the number of the 16S and the 23S rRNA genes in those strains is two, respectively. In contrast with the larger rRNAs, the number of 5S rRNA gene was different. In the strains of leptospires, L. biflexa, which were non-parasitic, there are two genes for 5S rRNA, whereas only one gene for 5S rRNA is carried in L. interrogans, which were originally isolated as parasitic. Southern hybridization experiments suggest that those rRNA genes are interspersed on the leptospiral chromosome.