Further characterization and in situ localization of chain-like aggregates of the gliding bacteria Myxococcus fulvus and Myxococcus xanthus

Abstract

For the first time, chain-like aggregates, called 'strands,' have been enriched from crude cell wall preparations of liquid-grown vegetative cells of two strains of Myxococcus xanthus. These strands are highly isomorphic to macromolecular structures, previously described for Myxococcus fulvus (Lunsdorf and Reichenbach, J. Gen. Microbiol. 135:1633-1641, 1989). The strands are morphologically composed of ring elements, consisting of six or more peripheral protein masses and possibly three small central masses. The ring elements are linked by two parallel strings of filamentous proteins, called elongated elements, which keep the ring elements at a constant distance. The overall dimensions of the ring elements are 16.6 ± 1.0 nm (n = 55) for M. xanthus Mx x48 and 16.4 ± 1.5 nm (n = 37) for M. xanthus DK 1622. The distance between the ring elements, as a measure of the length of the elongated elements, is 16.6 ± 1.1 nm (n = 59) for strain Mx x48 and 15.5 ± 0.6 nm (n = 41) for strain DK 1622. Characteristically, the strands and oligomeric forms thereof show a strict association with the outer membrane. In situ studies of freeze-fractured cells of M. fulvus showed ring elements, isomorphic to those described for M. xanthus, within the periplasm; they appeared in parallel rows just below the outer membrane but not in direct contact with the cytoplasmic membrane. A three-dimensional model summarizes the morphological data. It is hypothesized that the chain-like strands, as building blocks of a more complex belt-like continuum, represent the peripheral part of the gliding machinery, which transforms membrane potential energy into mechanical work.