Purification and Characterization of pili from Flavobacterium branchiophila

Abstract

The pili of Flavobacterium branchiophila ATCC 35035 were purified and characterized. After mechanical detachment from the bacterial cells, the pili were concentrated by ultrafiltration. The purification of the pili was carried out by ion-exchange chromatography on DEAE-cellulose. By electron microscopy, the purified pili were observed to be filaments measureing approximately 4 nm by 1μm The molecular weight of the protein subunits of the purified pili was determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. One protein subunit had a molecular weight of 23, 000 dalton, and the other faintly stained protein might be a dimer of the objective molecule. The purified pilus subunit was rich in aspartic acid and glutamic acid, alanine and glycine, but poor in histidine and methionine. Ultraviolet absorption spectrum of the purified pili showed a maximum absorption at 276 nm, and the extinction coefficient was calculated to be 41.0. In serological analysis, four strains of F. branchiophila produced a single common precipitin line against rabbit anti-pili serum. These results suggest that the pili are relatively homogeneous and a common structural component among the strains of F. branchiophila.