Fibrillar array in the cell wall of a gliding filamentous cyanobacterium

The cell walls of a number of filamentous, gliding cyanobacteria of the gen us Oscillatoria were examined by transmission electron microscopy of ultrat hin sections, of freeze-etched replicas, and of whole cells crushed between glass slides and negatively stained. All three techniques revealed the pre sence of a highly ordered array of parallel fibrils, seen in transverse sec tions to be situated between the peptidoglycan and the outer membrane, Appr oximately 200 individual fibrils, each 25 to 30 nm in width, form a paralle l, helical array that completely surrounds each cyanobacterial filament, ru nning at an angle of 25 to 30 degrees to its long axis. This highly regular arrangement of the fibrillar layer may imply some underlying symmetry resp onsible for its organization. A possible source of such symmetry would be t he peptidoglycan, and some form of interaction between this layer and the f ibrils might provide the necessary scaffolding for the fibrillar array. In crushed, negatively stained samples of fresh cells, individual fibrils were seen outside the filament, released from the cell wall, These released fib rils were of the same width as those observed in situ but were In short len gths, mostly of 100 to 200 nm. and were invariably bent, sometimes even int o U shapes, implying great flexibility, Negative staining of released fibri ls showed no evidence that they were hollow tubes but did give some indicat ion of a substructure. implying that they were composed of many subunits, T he function of this fibrillar array is unknown, although its position in th e cell wall, as well as the correspondence between the angle of the fibrils with respect to the long axis of the filament and the rotation of the fila ment during gliding, may imply an involvement in gliding motility.