DNA-DNA relatedness and phylogenetic positions of Slackia exigua, Slackia heliotrinireducens, Eggerthella lenta, and other related bacteria.

Recently, two asaccharolytic Eubacterium species, Eubacterium exiguum and Eubacterium lentum, and Peptostreptococcus heliotrinreducens have been reclassified as Slackia exigua, Eggerthella lenta and Slackia heliotrinireducens in the novel genera on the basis of 16S rDNA sequence analysis. But DNA-DNA relatedness among these species and other related bacteria have not been reported yet. DNA-DNA relatedness is the standard arbiter and the recommended method for the designation and evaluation of new species, particularly closely related ones. In the present study, DNA-DNA hybridization studies were performed on S. exigua, S. heliotrinireducens and E. lenta together with the other bacterial species in the related genera. The phylogenetic relationships of these species were also investigated by comparison analysis of 16S rDNA sequence data. In the DNA-DNA hybridization studies, S. exigua showed a DNA homology level of 33% to S. heliotrinireducens and 11% to E. lenta. DNA-DNA homology between S. heliotrinireducens and E. lenta was 10%. But these three species showed very low homology (less than 5%) to the related asaccharolytic species such as Eubacterium and Mogibacterium. In conclusion, the DNA-DNA relatedness data together with the evolutionary data in the present paper further support the reclassification of Eubacterium exiguum, Peptostreptococcus heliotrinreducens and Eubacterium lentum as Slackia exigua, Slackia heliotrinireducens and Eggerthella lenta, respectively.