Spatial patterns of ectoenzymatic kinetics in relation to biogeochemical properties in the Mediterranean Sea and the concentration of the fluorogenic substrate used

Van Wambeke, France; Pulido, Elvira; Catala, Philippe; Dinasquet, Julie; Djaoudi, Kahina; Engel, Anja; Garel, Marc; Guasco, Sophie; Marie, Barbara; Nunige, Sandra; Taillandier, Vincent; Zäncker, Birthe; Tamburini, Christian

Ectoenzymatic activity, prokaryotic heterotrophic abundances and production were determined in the Mediterranean Sea. Sampling was carried out in the sub-surface, the deep chlorophyll maximum layer (DCM), the core of the Levantine intermediate waters and in the deeper part of the mesopelagic layers. Michaelis–Menten kinetics were assessed using a large range of concentrations of fluorogenic substrates (0.025 to 50 inline-formulaµM). As a consequence, inline-formulaKm (Michaelis–Menten half-saturation constant) and inline-formulaVm (maximum hydrolysis velocity) parameters were determined for both low- and high-affinity enzymes for alkaline phosphatase, aminopeptidase (LAP) and inline-formulaβ-glucosidase (inline-formulaβGLU). Based on the constant derived from the high-LAP-affinity enzyme (0.025–1 inline-formulaµM substrate concentration range), in situ hydrolysis of N proteins contributed 48 % inline-formula± 30 % to the heterotrophic bacterial nitrogen demand within the epipelagic layers and 180 % inline-formula± 154 % in the Levantine intermediate waters and the upper part of the mesopelagic layers. The LAP hydrolysis rate was higher than bacterial N demand only within the deeper layer and only when considering the high-affinity enzyme. Based on a 10 % bacterial growth efficiency, the cumulative hydrolysis rates of C proteins and C polysaccharides contributed on average 2.5 % inline-formula± 1.3  % to the heterotrophic bacterial carbon demand in the epipelagic layers sampled (sub-surface and DCM). This study clearly reveals potential biases in current and past interpretations of the kinetic parameters for the three enzymes tested based on the fluorogenic-substrate concentration used. In particular, the LAP inline-formula M10inlinescrollmathml / 8pt14ptsvg-formulamathimg3af55808dad7e355d8e0b0b2a0272ce7 bg-18-2301-2021-ie00001.svg8pt14ptbg-18-2301-2021-ie00001.png inline-formulaβGLU enzymatic ratios and some of the depth-related trends differed between the use of high and low concentrations of fluorogenic substrates.

Zitieren

Zitierform:

Van Wambeke, France / Pulido, Elvira / Catala, Philippe / et al: Spatial patterns of ectoenzymatic kinetics in relation to biogeochemical properties in the Mediterranean Sea and the concentration of the fluorogenic substrate used. 2021. Copernicus Publications.

Zugriffsstatistik

Gesamt:
Volltextzugriffe:
Metadatenansicht:
12 Monate:
Volltextzugriffe:
Metadatenansicht:

Grafik öffnen

Rechte

Rechteinhaber: France Van Wambeke et al.

Nutzung und Vervielfältigung:

Export