Regulation of periphytic leucine-aminopeptidase activity

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 (NH 4 and NO 3 ) 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 Resale or republication not permitted without written consent of the publisherAquat Microb Ecol 31: [249][250][251][252][253][254][255][256][257][258] 2003 tein-degrading extracellular enzyme in aquatic systems (Chróst 1991(Chróst , 1993. This study examines the potential influence of several factors, including algal-bacterial coupling, on periphytic LAMP activity.Amino acids frequently serve as sources of both N and C for aquatic bacteria (Montuelle et al. 1992, Chróst 1993, Rosenstock & Simon 1993, Kroer et al. 1994, Keil & Kirchman 1999. Thus, it is likely that periphytic LAMP activity may be partially regulated by the availability of non-proteinaceous sources of nitrogen and labile organic carbon (LOC). Extracellular protease activity in natural planktonic communities and semi-natural culture systems can be reduced by additions of dissolved inorganic nitrogen (DIN; e.g. NH 4 , NO 3 ) (Chróst 1991, Francoeur et al. 2001, Sala et al. 2001), but LAMP activity can also be insensitive to DIN additions (Nausch & Nausch 2000). Previous experimental investigations of natural planktonic and benthic heterotrophic microbial communities have shown that additions of LOC (i.e. glucose, acetate) can decrease extracellular protease activity (Chróst 1991, Boetius & Lochte 1996a, but LAMP activity is not always affected by such additions (Boetius & Lochte 1996b, Mallet & Debroas 2000.Photosynthesis might be expected to affect LAMP activity through provision of LOC or alteration of pH. Several studies of freshwater habitats indicated that LAMP has a narrow pH optimum, ca. 7.5, with low activity at pH < 6 to 7 and rapid decline in activity above pH 8.5 to 9 (Halemejko &...

Effects of simulated short-term road salt exposure on lotic periphyton function

“…Glass fiber filters (47 mm diameter) were prepared by sandwiching sets of six filters between two 6 � 43 cm 2 plexiglass plates, one of which contained six circular openings (38 mm diameter) through which periphyton colonized the filters (see Kahn and Wetzel 1999;Francoeur and Wetzel 2003). The plexiglass plates were wired to bricks and placed on the streambed with the exposed surface of the filters facing upward and parallel to the streambed.…”

Biochemical quality of basal resources in a forested stream: effects of nutrient enrichment

“…In the fertilised reach and during the first period, the use of peptides is higher, potentially due to the higher availability of substrates for these enzymes (an increase in protein content in the biofilm). Moreover, higher leucine-aminopeptidase activities have been related to nutrient enrichment (Romaní et al 2004), incident light and photosynthetic activity (Espeland et al 2001;Francoeur and Wetzel 2003;Ylla et al 2009). At the end of the study period, the biofilm from the fertilised reach showed a decrease in phosphatase activity that was potentially related to the reduction of algal biomass and the availability of inorganic P, making phosphatase enzyme production unnecessary in the biofilm of the fertilised reach (Romaní et al 2004;Allison and Vitousek 2005).…”

“…Phosphatase is an enzyme that degrades orthophosphoric monoesters to inorganic P (Klotz 1992), b-glucosidase is involved in polysaccharide decomposition (Deshpande and Eriksson 1988), leucine-aminopeptidase activity is related to polypeptide hydrolysis, which is used to obtain leucine and other hydrophobic amino acids (Francoeur and Wetzel 2003), and lipase hydrolyses ester bonds in lipid substrates. These enzymes are derived from the microbial community, primarily heterotrophic bacteria (Romaní and Sabater 2001;Vrba et al 2004).…”

Release of dissolved free amino acids from biofilms in stream water

“…There may be several possible processes in which biofilms release DFAA into stream water: (1) epilithic and planktonic aminopeptidase activity [15] and/or periphytic extracellular aminopeptidase activity [18]; (2) …”

“…There are many possible factors affecting the DFAA compositions both inside and outside of the stream environment, such as soils, vegetation, litter, pollen, dew, and various microbial activity [13][14][15][16][17][18][19][20][21][22][23][24]. Among these factors, the roles of complex microbial communities called biofilms have been intensively investigated [25][26][27][28][29][30].…”