The Microaerophilic Nature of Treponema pallidum: Enhanced Survival and Incorporation of Tritiated Adenine Under Microaerobic Conditions in the Presence or Absence of Reducing Compounds

Treponema pallidum, although sensitive to atmospheric concentrations of O2, requires low levels of O₂, for optimal survival and metabolic activity. The addition of 0.0125-0.2 mg/ml of sodium metabisulfite to a basal medium consisting of Eagle's minimal essential medium and 50% fresh, heat-inactivated normal rabbit serum was found to have an effect similar to that of dithiothreitol in extending the survival of T. pallidum (Nichols strain) under 3% O₂. Detailed analysis of the effect of O₂ tension revealed that 50% motility was retained longest at atmospheric O₂ concentrations of 1-5%, whether or not dithiothreitol or sodium metabisulfite were present. Concentrations of O₂ of 3-10% were optimal for nucleic acid synthesis, as determined by [³H]adenine incorporation during the first 24 hr of incubation. Sodium metabisulfite was less effective than dithiothreitol in stimulating nucleic acid synthesis. Neither sodium metabisulfite nor dithiothreitol at their effective concentrations had any effect on levels of dissolved O₂. During incubation under 3% O₂, motility was maintained at >50% for 15 days and virulence for at least 13 days by dilution of the treponemal suspensions every three days with fresh medium containing sodium metabisulfite. The optimal retention of motility and nucleic acid synthesis under microaerobic conditions in the absence of reducing compounds provides further evidence that T. pallidum is a microaerophilic organism.