BIOCHEMICAL AND STRUCTURAL-ANALYSES OF THE EXTRACELLULAR-MATRIX FIBRILS OF MYXOCOCCUS-XANTHUS

It is characteristic of myxobacteria to produce large amounts of extra cellular material. This report demonstrates that this material in Myxo coccus xanthus is fibrillar and describes the structure and chemical c omposition of the fibrils. The extracellular matrix fibrils are the me diators of cell-cell cohesion in M. xanthus. As such, the fibrils play ad important role in the cell-cell interactions that form the basis f or the Social and developmental lifestyle of this organism. The fibril s are composed of protein and carbohydrate in a 1.0:1.2 ratio. Combine d, the two fractions accounted for greater than 85% of the mass of iso lated fibrils, and the fibrils were found to compose up to 10% of the dry weight of cells grown at high density on a solid surface. The poly saccharide portion of the fibrils was shown to be composed of five dif ferent monosaccharides: galactose, glucosamine, glucose, rhamnose, and xylose. Glucosamine, one of the component monosaccharides of the fibr ils and a known morphogen for M. xanthus, inhibited cohesion to a leve l near that of Congo red (the positive control for cohesion inhibition ). Glucose and xylose also inhibited cohesion but less than did glucos amine. Analysis of the morphology of the fibrils, the periodicities wi thin the distribution of fibril diameters observed by field emission s canning electron microscopy, and the observation of fibrils on hydrate d cells strongly suggested that the extracellular matrix of M. xanthus was indeed arranged is fibrils. Furthermore, results suggested that t he fibrils were constructed as carbohydrate structures with associated proteins.