DIVERSITY AMONG FIBROBACTER ISOLATES - TOWARDS A PHYLOGENETIC CLASSIFICATION

Genetic diversity among 15 strains of Fibrobacter succinogenes and F. intestinalis was evaluated by comparative 16S rRNA sequencing, by estimation of genomic DNA similarity, and by restriction endonuclease digestion patterns. The previous division of the genus into two genetically well-resolved species (F. succinogenes and F. intestinalis) was confirmed by the additional comparative studies. All measures of genomic relatedness were consistent. The two species were related at approximately 91 to 93%, 16S rRNA sequence similarity and less than 20% genomic DNA similarity. F. succinogenes subsp. elongata was found to comprise three subgroups related at ca 97% 16S rRNA sequence similarity; although subspecies status would be phylogenetically justifiable, difficulties in phenotypic distinction of these subgroups contraindicate formation of additional subspecies. Analysis of all pairwise comparisons showed that 50%, DNA-DNA pairing corresponded to approximately 99% 16S rRNA sequence similarity.