Phylogenetic heterogeneity within the genus Herpetosiphon: transfer of the marine species Herpetosiphon cohaerens, Herpetosiphon nigricans and Herpetosiphon persicus to the genus Lewinella gen. nov. in the Flexibacter-Bacteroides-Cytophaga phylum

This study analyzed 16S rDNA sequences from Herpetosiphon species to determine their phylogenetic relationships. The results revealed unexpected heterogeneity within the genus. The thermotolerant freshwater species Herpetosiphon geysericola clustered with the type species H. aurantiacus in the green non-sulfur bacteria subdivision alongside Chloroflexus. However, three marine species—H. cohaerens, H. nigricans, and H. persicus—formed a distinct phylogenetic cluster within the Flexibacter–Bacteroides–Cytophaga (FBC) phylum's Saprospira group, alongside the non-motile bacterium Haliscomenobacter hydrossis. Because these marine species were phylogenetically distant from H. aurantiacus, the authors propose transferring them to a new genus, Lewinella gen. nov., as L. cohaerens, L. nigricans, and L. persica. The marine gliding bacterium Flexithrix dorotheae was confirmed as an FBC member but on a separate phylogenetic line from the newly classified Lewinella species. This work demonstrates that gliding motility and sheathed filament morphology are not phylogenetically informative features and have evolved convergently across multiple bacterial lineages.

Key findings

• 16S rDNA sequence analysis revealed Herpetosiphon geysericola is phylogenetically related to H. aurantiacus in the green non-sulfur bacteria
• The three marine Herpetosiphon species (H. cohaerens, H. nigricans, H. persicus) belong to the FBC phylum's Saprospira group and are unrelated to the genus type species
• Three marine Herpetosiphon species are proposed for transfer to new genus Lewinella based on phylogenetic evidence
• Gliding motility and ensheathed filament morphology are not reliable phylogenetic markers, having evolved independently in multiple bacterial lineages