RELATIONSHIP OF TREPONEMA-DENTICOLA PERIPLASMIC FLAGELLA TO IRREGULARCELL MORPHOLOGY

Treponema denticola is an anaerobic, motile, oral spirochete associate d with periodontal disease. We found that the periplasmic flagella (PF s), which are located between the outer membrane sheath and cell cylin der, influence its morphology in a unique manner. In addition, the pro tein composition of the PFs was found to be quite complex and similar to those of other spirochetes. Dark-field microscopy revealed that mos t wild-type cells had an irregular twisted morphology, with both plana r and helical regions, and a minority of cells had a regular right-han ded helical shape. High-voltage electron microscopy indicated that the PFs, especially in those regions of the cell which were planar, wrapp ed around the cell body axis in a right-handed sense. In those regions of the cell which were helical or irregular, the PFs tended to lie al ong the cell axis. The PFs caused the cell to form the irregular shape , as two nonmotile, PF-deficient mutants (JR1 and HL51) were no longer irregular but were right-handed helices. JR1 was isolated as a sponta neously occurring nonmotile mutant, and HL51 was isolated as a site-di rected mutant in the flagellar hook gene flgE. Consistent with these r esults is the finding that wild-type cells with their outer membrane s heath removed were also right-handed helices similar in shape to JR1 a nd HL51. Purified PFs were analyzed by two-dimensional gel electrophor esis, and several protein species were identified. Western blot analys is using antisera to Treponema pallidum PF proteins along with N-termi nal amino acid sequence analysis indicated T. denticola PFs are compos ed of one class A sheath protein of 38 kDa (FlaA) and three class B pr oteins of 35 kDa (FlaB1 and FlaB2) and one of 34 kDa (FlaB3). The N-te rminal amino acid sequences of the FlaA and FlaB proteins of T. dentic ola were most similar to those of T. pallidum and Treponema phagedenis . Because these proteins were present in markedly reduced amounts or w ere absent in HL51, PF synthesis is likely to be regulated in a hierar chy similar to that found for flagellar synthesis in other bacteria.