The role of fungi in the diet of the amphipodGammarus pulex(L.): an enzymatic study

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Abstract
SUMMARY.1. Sets of tenGammarus pulexfed on controlled diets of sterile alder leaves, or fungal mycelium, or alder leaves incubated for 10 days with an aquatic hyphomycete, were assayed for cellulase, β‐1,3‐glucanase an d chiitinase activity and compared with (a) animals taken directly from the stream, (b) animals starved for 2 days, and (c) enzyme activity in fungal mycelium.2. Gut enzyme activity was compared on natural substrates of sterile leaves, mycelium and inoculated leaves as well as on model substrates.3.G. pulexsecretes an endogenous coupled cellulase system capable of degrading native cellulose in plant cell walls. It also secretes β‐1,3‐glucanase and chitinase capable of degrading fungal cell walls thus affording access for gut enzymes to cell contents.4. Secretion of enzymes active on native cellulose is enhanced on a diet of leaves already partially degraded by fungal enzymes. Gut enzymes extract more reducing sugar from this substrate than from sterile leaves. Specific enzyme secretion is enhanced by the presence in the diet of exposed, accessible substrates. Fungal enzymes do not appear to contribute to the digestive processes ofG. pulex.