Ectohydrolase activity in surface waters of the Hudson River and western Long Island Sound estuaries

Abstract

Variability in hydrolytic ectoenzyme activity was investigated at 3 stations along the salinity gradient of the Hudson River estuary and at 1 station in western Long Island Sound between October 1996 and October 1998. Activities of aminopeptidase, β-glucosidase, chitinase, lipase and alkaline phosphatase were estimated at each station using fluorogenic substrate analogs (methylumbelliferyl [MUF]-and methylcoumarinylamide [MCA]-labeled). Potential hydrolysis rate constants for these ectohydrolases varied widely over time and among stations; from < 0.01 to 90% d -1 . Most rate constants were highest in July and August. However, temperature only weakly correlated with activities of 4 of the 5 ectohydrolases in the Hudson River (r = 0.35 -0.58, x = 0.42) and was not significantly correlated with activity of any ectohydrolase in Long Island Sound. Activities of most ectohydrolases varied independently of dissolved and particulate organic carbon, bacterial abundance, chlorophyll a and primary production. Aminopeptidase activity was strongly correlated with bacterial production (r = 0.78-0.89; p < 0.0001; n = 46) and negatively with total inorganic nitrogen concentration (r = -0.57; p < 0.0001; n = 47) among all stations. However, each station had distinct enzyme activity profiles, suggesting acclimation of bacterial communities to different nutritional regimes. For example, alkaline phosphatase and aminopeptidase activity dominated the oligohaline station, while at the marine station, activity was more evenly divided among all ectohydrolases but lipase. Activities of aminopeptidase, β-glucosidase and chitinase were highly correlated with turnover of 3 H-leucine, 14 C-glucose and 14 C-acetate, suggesting a close coupling between hydrolysis of polymeric source materials and consumption of a variety of monomeric products.

Bottom up effects on bacterioplankton growth and composition during summer-autumn transition in the open NW Mediterranean Sea

“…However, this author noticed also large day-to day fluctuations of ectoenzymatic activity and a prominent presence of lipase activity among isolates. Finally, nothing is known about the difference that can be obtained by using MUF-oleate (unsaturated fatty acid analog 18:1) and MUF-palmitate (saturated fatty acid analog 16:0 that we used) as fluorogenic substrates (Taylor et al, 2003).…”

Automated high resolution ectoenzyme measurements: instrument development and deployment in three trophic regimes

“…The Hudson River estuary experiences eutrophication from nutrient input in the New York/ New Jersey area (Taylor et al 2003). During the 8 April 2005 -20 April 2005 cruise aboard the RV Oceanus, EAAS sampled the ship's uncontaminated seawater system in the dry lab for peptidase using Leu-AMC as the substrate and a 5 min incubation.…”

“…High fluorescence yield and low background fluorescence will increase assay sensitivity (Ammerman and Glover 2000). Previous enzyme activity measurements have used incubation times ranging from a few hours to multiple days in oligotrophic regions (Perry 1972;Christian and Karl 1995;Taylor et al 2003;Kirchman et al 2004;Sebastian et al 2004). Although increasing incubation time does not affect the detection limit of fluorescence (there is no change in the quantum yield of the fluorescent compound), it does allow lower activities to be measured.…”

Dissolved organic matter and persistence of the invasive zebra mussel (Dreissena polymorpha) under low food conditions

“…At that rate, the mussels should have removed .80% of the entire free amino acid pool, excluding glutamate and aspartate, less than a day after each change of water (Baines et al 2005). Such a depletion is unlikely in situ, where zebra mussels typically filter a fraction of their ambient environment daily (Strayer 1999) and free amino acid pools are quickly turned over through the ectohydrolytic activity of microbes (Taylor et al 2003). If mussels in our experiments were in fact depleting these labile DOM pools, then the difference in growth rate between the high DOM and low DOM treatments should be greater when the water is replaced more frequently.…”