EVIDENCE FOR A NEW-TYPE OF OUTER-MEMBRANE LIPID IN ORAL SPIROCHETE TREPONEMA-DENTICOLA - FUNCTIONING PERMEATION BARRIER WITHOUT LIPOPOLYSACCHARIDES

A new class of outer membrane lipid (OML) was isolated from the oral s pirochete Treponema denticola strain ATCC 33521 using a phenol/chlorof orm/light petroleum procedure normally applied far lipopolysaccharide extraction. In addition to chemical analysis, Fourier transform infrar ed (FTIR) spectroscopy was applied to compare the biophysical properti es of OML with lipopolysaccharides (LPS) and lipoteichoic acids (LTA), Isolated OML fractions represent 1.4% of the total dry cell weight, a re about 4 kDa in size, and contain 6% amino sugars, 8% neutral sugars , 14% phosphate, 35% carbazol-positive compounds, and 11% fatty acids (containing iso-and anteiso-fatty acyl chains), Rare for outer membran e lipids, OML contains no significant amount of 3-deoxy-D-manno-octulo sonic acids, heptoses, and beta-hydroxy fatty acids. The fatty acyl ch ain composition, being similar to that of the cytoplasmic membrane, is quite heterogeneous with anteiso-pentadecanoic acid (12%), palmitic a cid (51%), and iso-palmitic acid (19%) as the predominant fatty acids present. Findings of a glycerol-hexose unit and two glycerol-hexadecan oic acid fragments indicate a glycolipid membrane anchor typically fou nd in LTA. There was also no evidence for the presence of a sphingosin e-based lipid structure. The results of FTIR measurements strongly sug gest that the reconstituted lipid forms normal bilayer structures (ves icles) expressing a high membrane state of order with a distinct phase transition as typical for isolated LPS, However, in contrast to LPS, OML of T. denticola has a lower T-m near 22 degrees C and a lower coop erativity of the phase transition. The results suggest a different kin d of permeation barrier that is built lip by this particular OML of T. denticola, which is quite different from LPS normally essential for G ram-negative bacteria.