Extracellular enzyme activities associated with epiphytic microbiota on submerged stems of the reed Phragmites australis

Abstract

Fluorogenic 4-methylumbelliferyl (MUF) compounds were used as analogue substrates for assay of extracellular enzyme activities associated with epiphytic microbiota at submerged Phragmites australis stem surfaces. Incubations at a range of MUF substrate concentrations indicated that saturation of enzyme activity was achieved at a MUF substrate concentration of about 200 μmol 1 −1. Later determinations at a single, saturation, concentration of MUF substrate were, therefore, carried out at about 200 μmol l −1. Such determinations were undertaken using P. australis stems from eight gravel-pit ponds. The rate of enzymatic hydrolysis of MUF phosphate (analogue substrate for phosphatase activity) was > MUF β- d-glucopyranoside (β- d-glucosidase) > MUF β- d-galactopyranoside (β- d-galactosidase) > MUF sulphate (sulphatase) and MUF palmitate (lipase) on stems from all eight ponds. Thus the relative magnitude of the various components of total epiphyton extracellular enzyme activity might be a conservative feature.