Inositol-phosphodihydroceramides in the periodontal pathogen Tannerella forsythia: Structural analysis and incorporation of exogenous myo-inositol

BACKGROUND: Unique phosphodihydroceramides containing phosphoethanolamine and glycerol have been previously described in Porphyromonas gingivalis. Importantly, they were shown to possess pro-inflammatory properties. Other common human bacteria were screened for the presence of these lipids, and they were found, amongst others, in the oral pathogen Tannerella forsythia. To date, no detailed study into the lipids of this organism has been performed. METHODS: Lipids were extracted, separated and purified by HPTLC, and analyzed using GC-MS, ESI–MS and NMR. Of special interest was how T. forsythia acquires the metabolic precursors for the lipids studied here. This was assayed by radioactive and stable isotope incorporation using carbon-14 and deuterium labeled myo-inositol, added to the growth medium. RESULTS: T. forsythia synthesizes two phosphodihydroceramides (Tf GL1, Tf GL2) which are constituted by phospho-myo-inositol linked to either a 17-, 18-, or 19-carbon sphinganine, N-linked to either a branched 17:0(3-OH) or a linear 16:0(3-OH) fatty acid which, in Tf GL2, is, in turn, ester-substituted with a branched 15:0 fatty acid. T. forsythia lacks the enzymatic machinery required for myo-inositol synthesis but was found to internalize inositol from the medium for the synthesis of both Tf GL1 and Tf GL2. CONCLUSION: The study describes two novel glycolipids in T. forsythia which could be essential in this organism. Their synthesis could be reliant on an external source of myo-inositol. GENERAL SIGNIFICANCE: The effects of these unique lipids on the immune system and their role in bacterial virulence could be relevant in the search for new drug targets.