Purification and preliminary characterization of Spiroplasma fibrils

Fibrils 3.5 nm in diameter were released from the honeybee spiroplasma (BC3) by treatment with detergents and then purified by isopycnic centrifugation. Purified fibrils were flexuous, of indeterminate length, and had an axial repeat of 8.5 nm. The fibrils were associated in pairs, but in 1 M salt formed aggregates with a marked striated appearance. Pronase completely degraded the fibrils, but trypsin had little effect. The fibrils were composed of a single protein of molecular weight 55,000 which represented about 1% of the total cell protein. A protein of molecular weight 26,000 appeared to be associated with the fibrils. The significance of this in relation to membrane attachment and the possible role of fibrils in maintenance of cell shape and in motility are discussed.