Surface ultrastructure and chemical composition of the cell walls of conidial fungi

Abstract

Freeze-fractures of the conidial wall surface of the deuteromycetous fungi Penicillium sp., Cladobotryum varium, Cladosporium macrocarpum, and Aspergillus niger and of the sporangiospore surface of the zygomycetous fungus Mycotypha microspora reveal rodlet fascicles. Shadow replicas and deep-etching of these cells demonstrate an outermost amorphous layer adjacent to the rodlet fascicles. In each case, individual rodlets are apparently composed of chains of subunits (approx 50 A diam) while interdigitated fascicles consist of clusters of rodlets arranged in parallel. The conidial wall of A. niger was separated into an outer and inner layer by passing the cells through a cell fractionator. Rodlets were present on the extracellular surface of the isolated and purified outer layer, but absent from the inner layer. The hyphal wall of A. niger was also isolated and purified. A comparison of the chemical composition of the three wall layers demonstrated distinct quantitative differences in total carbohydrate, monosaccharide, total hexosamine, peptide, and lipid content. On the basis of the gross chemical composition of the outer conidial wall layer, as well as data obtained from enzymatic digestion and various chemical treatments of this layer followed by ultrastructural examinations, it is suggested that rodlets of A. niger are mainly proteinaceous.