AME 31:249-258 (2003)  -  doi:10.3354/ame031249

Regulation of periphytic leucine-aminopeptidase activity

Steven N. Francoeur1,2,*, Robert G. Wetzel1,3

1Department of Biological Sciences, The University of Alabama, Tuscaloosa, Alabama 35487-0206, USA
2Present address: Department of Biology, Eastern Michigan University, 316 Mark Jefferson, Ypsilanti, Michigan 48197, USA
3Present address: Department of Environmental Sciences and Engineering, The University of North Carolina, Chapel Hill, North Carolina 27599-7431, USA

ABSTRACT: Short-term (<24 h) regulation of leucine-aminopeptidase (LAMP) activity in constructed and natural periphyton communities was investigated experimentally. Supply of dissolved inorganic nitrogen (NH4 and NO3) and labile organic carbon (glucose), and active periphytic photosynthesis all affected LAMP activity, and these factors often displayed interactive effects. The variable influence of regulatory factors among experiments and frequent interactive effects indicated that regulation of LAMP activity is a complex, temporally dynamic process. Responses of putatively bacterial LAMP activity to algal photosynthesis suggested that extracellular protease activity is another periphytic process moderated by algal-bacterial coupling. Periphytic LAMP pH optima (pH > 9.75) were much greater than those previously reported for planktonic communities and profundal sediments (pH 7.5 to 8.0), suggesting a mechanism by which photosynthesis could stimulate LAMP activity. In situ LAMP activity of natural wetland periphyton communities displayed diurnal patterns consistent with stimulation of LAMP activity by photosynthetically-induced pH shifts, but was also directly correlated with the potentially causal factors of dissolved inorganic nitrogen concentration and temperature.

KEY WORDS: Periphyton · Biofilm · Extracellular enzymes · Algal-bacterial interaction

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