Phylogenetic foundation of spirochetes

Area of Science:

• Microbiology
• Bacteriology
• Phylogenetics

Background:

• Spirochetes are helical bacteria, existing freely or within hosts, with some species causing disease in humans and animals.
• Phylogenetic analysis using 16S rRNA sequences confirms spirochetes as a distinct monophyletic phylum within the bacterial domain.
• Current classification places spirochetes in the Class Spirochaetes, Order Spirochetales, divided into three main families: Spirochaetaceae, Brachyspiraceae, and Leptospiraceae.

Purpose of the Study:

• To review the current classification and phylogenetic understanding of spirochetes.
• To highlight the existence and identification of novel, unculturable spirochetal species (phylotypes).
• To emphasize the substantial unrecognized diversity within the spirochete phylum.

Main Methods:

• Comparative analysis of 16S rRNA gene sequences for phylogenetic classification.
• Identification of novel spirochetal phylotypes from various environmental and host-associated niches.
• Review of existing taxonomic classifications and literature.

Main Results:

• Spirochetes are classified into three families: Spirochaetaceae (including Borrelia, Treponema), Brachyspiraceae (Brachyspira), and Leptospiraceae (Leptospira).
• Over 200 spirochetal species or phylotypes have been identified, with more than half currently unculturable in vitro.
• Novel unculturable spirochetes have been detected in diverse environments, including the human oral cavity and termite gut.

Conclusions:

• The study underscores the significant and largely unexplored diversity of spirochetes.
• Further research is needed to cultivate and characterize the numerous uncultured spirochetal species.
• Understanding this hidden diversity is crucial for a comprehensive view of bacterial ecosystems and potential pathogenicity.