Summary auto-generated
This study analyzed 16S-23S rDNA internal transcribed spacer (ITS) sequences from all known Fusobacterium species and related bacteria to clarify their phylogenetic relationships. Researchers designed new universal PCR primers to amplify the ITS region from 33 bacterial strains. Analysis of ITS length patterns and DNA sequences revealed that most Fusobacterium species produced one major and two to three weaker bands (800-830 bp and 1000-1100 bp). ITS sequencing provided high phylogenetic resolution, identifying conserved motifs for alignment and variable sites for species differentiation. The analysis revealed three major Fusobacterium groups: the mortiferum/varium/ulcerans cluster, the nucleatum/simiae/periodonticum/naviforme cluster, and the necrophorum/gonidiaformans group. Notably, Fusobacterium prausnitzii showed only 48% similarity to the Fusobacterium nucleatum type species—closer related genera like Leptotrichia and Sebaldella were more similar—suggesting Fusobacterium prausnitzii requires reclassification. Fusobacterium russii and perfoetens formed separate evolutionary branches. Some species pairs (F. necrophorum subspecies and F. varium/mortiferum) showed >98% ITS sequence identity yet remain distinguishable by morphology and biochemical tests.
Key findings
- ITS sequences provide higher phylogenetic resolution than 16S rRNA sequences alone for differentiating Fusobacterium species and subspecies
- Fusobacterium prausnitzii is phylogenetically distant from core Fusobacterium species and requires reclassification into a different genus
- Three major phylogenetic clusters were identified within Fusobacterium: the mortiferum/varium group, the nucleatum/simiae group, and the necrophorum group
- Some closely related species pairs (F. necrophorum subspecies; F. varium/mortiferum) are >98% identical at the ITS level but remain phenotypically distinguishable
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Abstract
The 16S--23S rDNA internal transcribed spacer (ITS) regions of all currently defined Fusobacterium species and related taxa such as Leptotrichia buccalis, Sebaldella termitidis and Streptobacillus moniliformans, were analysed to examine inter- and intraspecies as well as subspecies relationships. For the ITS-amplification, a new eubacterial universal primer pair was designed and used. The majority of the Fusobacterium strains, along with L. buccalis showed one major, and two to three weaker, distinct bands (short and long versions) with lengths of 800--830 bp and 1000--1100 bp. Nevertheless, six other patterns were also found within the genus Fusobacterium, demonstrating its heterogeneity. The ITS region was sequenced and found to consist both of conserved motifs, which functioned as a framework for alignment, and of variable sites, which provided high phylogenetic resolution. Analyses of the ITS-DNA sequences and ITS relative length (short version) allowed species and subspecies differentiation in most cases. The results confirmed the strikingly distant relationship between Fusobacterium prausnitzii and the genus Fusobacterium. Fusobacterium nucleatum subspecies, along with Fusobacterium naviforme, Fusobacterium simiae and Fusobacterium periodonticum, formed a cluster with an inherently high potential for diversification. Other clusters were formed by Fusobacterium necrophorum subspecies with Fusobacterium gonidaformans and by Fusobacterium varium with Fusobacterium mortiferum and Fusobacterium ulcerans. Fusobacterium russii as well as Fusobacterium perfoetens formed separate branches. Fusobacterium necrophorum subspp. necrophorum and funduliforme on the one hand, and Fusobacterium varium and Fusobacterium mortiferum on the other, were found to be very similar, even at the high-resolution ITS level.