Chitin and ?(1?3) glucan synthases in the protoplastic entomophthorales

Abstract

β(1–3) glucan and chitin synthases were studied in spontaneously produced protoplasts and in the mycelium (hyphal body) of the entomopathogenic Entomophthorale species Entomophaga aulicae, Conidiobolus obscurus and Entomophthora muscae. The absence of wall in protoplasts was correlated to an absence of chitin synthase and to a very low β(1–3) glucan synthase activity, whereas these two polysaccharide synthases were present and active in the walled hyphal bodies. Physicochemical properties of chitin and β(1–3) glucan synthases such as localization, optimum pH and temperature, activation by disaccharides and proteases were similar to those found in other fungi unable to spontaneously produce protoplasts and could not be related to the ability for protoplastic Entomophthorale species to produce and proliferate under a protoplast form. The absence or the low chitin and glucan synthase activites in Entomophthorale protoplasts was not due to an absence of proteolytic activation of the enzyme. However, all protoplast fractions contained inhibitory substances of glucan and chitin synthase activities. These inhibitors were stable and specific of the protoplast stage. They were not glucanase nor chitinase. These results suggest that the absence of wall synthesis in Entomophthorale protoplasts is due to a continuous inhibition of β(1–3) glucan and chitin synthase activities by intracellular compounds and also for glucan synthase by protoplast medium constituents such as NaCl and fetal calf serum.