Structure and Composition of Walls of the Yeast Form of Verticillium albo-atrum

SUMMARY: Walls of the yeast form of Verticillium albo-atrum showed a granular appearance on the outer surface. The granular components could be extracted by alkali, revealing a fibrillar wall fabric. A region of circularly oriented microfibrils with a minute central ‘orifice’ was commonly found at one of the cell poles and probably represented a bud scar. The material dissolved by alkali was a heteropolysaccharide-protein complex containing mannose, galactose, glucose, glucuronic acid, glucosamine and the common range of amino acids. The alkali-insoluble microfibrillar network was made of a β-linked glucan and chitin. The glucan was digested by endo-β-glucanases yielding glucose, β-1,3-linked glucose oligomers and cellobiose, but no evidence for cellulose was found. Most of the glucan was also soluble in hot acid. The acid-insoluble glucan (hydroglucan) contained β-1,6-links. Acid treatment produced coarse microfibrils resembling those in Saccharomyces cerevisiae walls treated similarly. The hydroglucan was soluble in alkali leaving an insoluble microfibrillar network composed mainly of chitin. A small amount of lipid (2.7 to 3.4%), mostly of the bound type, and traces of phosphate were also found.