Composition and enzymatic activity of the extracellular matrix secreted by germlings of Botrytis cinerea

Germlings of Botrytis cinerea, an important fungal pathogen of plants, produce an extracellular matrix (ECM), or ensheathing film, that serves, in part, in their attachment (R. P. Doss, et al., Appl. Environ. Microbiol. 61: 260-265, 1995). The composition of this film has been ascertained by using samples obtained by growing germlings on a glass surface, removing the fungal mycelium by vigorous washing, and collecting the tightly attached film by scraping the substratum with a razor blade. Slightly over half of the dry weight of the ECM was found to be carbohydrates (about 20%), proteins (about 28%), and lipids (about 6%). Hydrolysis of the carbohydrate portion of the ECM revealed that glucose was the most prominent monosaccharide present, comprising about 60% of the total monosaccharides. Also present were mannose (about 35%) and myo-inositol (about 5%). The proteinaceous fraction of the ECM was made up of a number of polypeptides separable by polyacrylamide gel electrophoresis. The lipid fraction of the ECM, analyzed by thin-layer chromatography, was made up of several simple lipid components, including free fatty acid, mono- and triacylglycerol, wax ester, fatty alcohol, and several unidentified components. No complex lipids were detected. Isolated ECM exhibited polygalacturonase and laccase activity and was able to catalyze the hydrolysis of p-nitrophenyl butyrate, a model substrate for assessing cutinase activity. Cellulase, pectin lyase, and pectin methyl esterase activities were noted with both heated and unheated ECM preparations. Proteinase activity was not detected.