title: Periphytic photosynthetic stimulation of extracellular enzyme activity in aquatic microbial communities associated with decaying typha litter.
abstract: We examined the effect of light on extracellular enzyme activities of periphytic/endogenous microbial assemblages associated with decomposing litter of an emergent macrophyte Typha angustifolia within a small inland wetland in southeastern Michigan. Standing-dead Typha leaf litter was collected, placed into floating wire mesh litter baskets, and submerged in a wetland pool. Enzyme saturation assays were conducted on three occasions following litter submergence (days 9, 28, and 44) to generate saturation curves for the individual enzymes tested and to examine potential differences in enzyme saturation kinetics during microbial colonization and development. Experimental light manipulations were conducted on two occasions during microbial development (days 10 and 29). Short-term (30 min) light exposure significantly increased extracellular beta-glucosidase activity of litter-associated microbial communities. Activities of beta-xylosidase and leucine-aminopeptidase were not stimulated, and stimulation of phosphatase activity was variable. The exact mechanism for increased enzyme activity remains unknown, but it may have been increased pH arising from periphytic algal photosynthesis. These results suggest that extracellular enzyme activity in microbial communities colonizing natural organic substrata may be influenced by light/photosynthesis, as has previously been demonstrated for periphyton communities grown on artificial, inert substrata. Thus, light/photosynthetic mediated stimulation of extracellular enzyme activities may be a common occurrence in microbial communities associated with natural decaying plant litter in wetlands and might engender diurnal patterns in other microbial decay processes (e.g., production, organic matter decomposition, and mineralization).
authors.affiliation: Department of Biology, Eastern Michigan University, 316 Mark Jefferson Hall, Ypsilanti, MI 48197, USA. steve.francoeur@emich.edu
authors.forename: Steven N
authors.initials: SN
authors.lastname: Francoeur
authors.forename: Mark
authors.initials: M
authors.lastname: Schaecher
authors.forename: Robert K
authors.initials: RK
authors.lastname: Neely
authors.forename: Kevin A
authors.initials: KA
authors.lastname: Kuehn
mesh_terms: D001419:Bacteria / Q000254:growth & development / Q000378:metabolism; D018533:Biomass; D017753:Ecosystem; D004789:Enzyme Activation / Q000528:radiation effects; D056890:Eukaryota / Q000254:growth & development / Q000502:physiology*; D005110:Extracellular Space / Q000201:enzymology; D005658:Fungi / Q000254:growth & development / Q000378:metabolism; D008027:Light; D008824:Michigan; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism; D010788:Photosynthesis / Q000502:physiology* / Q000528:radiation effects; D032401:Typhaceae / Q000382:microbiology*; D053833:Wetlands; D001617:beta-Glucosidase / Q000378:metabolism
chemical_list: D010744:Phosphoric Monoester Hydrolases; D001617:beta-Glucosidase