OCCURRENCE OF FRAGMENTED 16S RIBOSOMAL-RNA IN AN OBLIGATE BACTERIAL ENDOSYMBIONT OF PARAMECIUM-CAUDATUM

The phylogenetic position of Caedibacter caryophila, a so far noncultu red killer symbiont of Paramecium caudatum, was elucidated by comparat ive sequence analysis of in vitro amplified 16S rRNA genes (rDNA). C. caryophila is a member of the alpha subclass of the Proteobacteria phy lum. Within this subclass C. caryophila is moderately related to Holos pora obtusa, which is another obligate endosymbiont of Paramecium caud atum, and to Rickettsia. A 16S rRNA targeted specific hybridization pr obe was designed and used for in situ detection of C. caryophila withi n its host cell. Comparison of the 16S rDNA primary structure of C. ca ryophila with homologous sequences from other bacteria revealed an unu sual insertion of 194 base pairs within the 5'-terminal part of the co rresponding gene. The intervening sequence is not present in mature 16 S rRNA of C. caryophila. It was demonstrated that C. caryophila contai ned fragmented 16S rRNA.