Phosphatase activity of four ectomycorrhizal fungi found in a Sitka spruce-Japanese larch plantation in Ireland

Abstract

Ectomycorrhizal fungi (Paxillus involutus, Suillus grevillei and two unidentified basidiomycetes from excised Sitka spruce mycorrhizas) were isolated from stands of Sitka spruce either in monoculture or in mixture with Japanese larch in an Irish conifer plantation. They were grown for 35 d on modified Melin-Norkrans liquid medium containing ferric phytate as the phosphorus source. The cultures were then separated into wall- and membrane-bound, cytoplasmic and extracellular fractions and assayed for phosphatase. Wall- and membrane-bound fractions contained the most active acid phosphatase. The unidentified basidiomycetes showed a lower substrate affinity and higher velocity of reaction than P. involutus and S. grevillei. Wall- and membrane-bound and cytoplasmic phosphatase activities were optimum over a broad pH range (4·0–6·0). Various methods were used to release the wall-bound phosphatase and a high proportion (49–88%) appeared to be tightly held within the wall. Phosphatase released from the wall by sonication had a similar Km to wall-bound phosphatase but Vmax was lower. The use of a number of substrates demonstrated a high affinity for inorganic pyrophosphate and sodium β-glycerophosphate but a low phytase activity.