Mycelial responses of the soil fungus, Mortierella isabellina, to grazing by Onychiurus armatus (collembola)

Abstract

Hyphal morphology and extracellular enzyme production of the fungus Mortierella isabellina were studied during grazing by a soil Collembola, Onychiurus armatus. Grazing induced switching from a “normal” hyphal mode, with appressed growth and sporulating hyphae, to fan shaped sectors of fast growing and nonsporulating mycelium which developed extensive aerial mycelium. Specific protease and α-amylase activities were several times higher in grazed cultures where switching occurred compared with plates without switching. Increased protease activity was localized to switched sectors within the mycelium. On the basis of inhibitor studies, the protease of “normal” mycelium was classified as a metalloprotease. Switching induced activity of an additional serine protease. Anion-exchange chromatography showed that the two proteases had similar charges and, according to SDS-gclatine-PAGE. the molecular weight of the serine protease was 80.000. Switching to a fast growing hyphal mode could be one explanation for compensatory growth of grazed fungi.