Spatial patterns of ectoenzymatic kinetics in relation to biogeochemical properties in the Mediterranean Sea and the concentration of the fluorogenic substrate used
Type | Article | ||||||||||||||||||||
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Date | 2021-04 | ||||||||||||||||||||
Language | English | ||||||||||||||||||||
Author(s) | Van Wambeke France1, Pulido Elvira1, Catala Philippe3, Dinasquet Julie2, 3, Djaoudi Kahina1, 4, Engel Anja5, Garel Marc1, Guasco Sophie1, Barbara Marie3, Nunige Sandra1, Taillandier Vincent6, Zancker Birthe6, 7, Tamburini Christian1 | ||||||||||||||||||||
Affiliation(s) | 1 : Aix-Marseille Université, CNRS/INSU, Université de Toulon, IRD, Mediterranean Institute of Oceanography (MIO) UM 110, 13288, Marseille, France 2 : Marine Biology Research Division, Scripps Institution of Oceanography, UCSD, La Jolla, USA 3 : Sorbonne Universités, UPMC University Paris 6, Laboratoire d'Océanographie Microbienne (LOMIC), Observatoire Océanologique, 66650, Banyuls/mer, France 4 : Molecular and Cellular Biology, The University of Arizona, Tucson, USA 5 : GEOMAR – Helmholtz-Centre for Ocean Research, Kiel, Germany 6 : CNRS, Sorbonne Universités, Laboratoire d’Océanographie de Villefranche (LOV), UMR7093, 06230 Villefranche sur-Mer, France 7 : The Marine Biological Association of the UK, Plymouth, United Kingdom |
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Source | Biogeosciences (1726-4170) (Copernicus GmbH), 2021-04 , Vol. 18 , N. 7 , P. 2301-2323 | ||||||||||||||||||||
DOI | 10.5194/bg-18-2301-2021 | ||||||||||||||||||||
WOS© Times Cited | 6 | ||||||||||||||||||||
Note | Special issue | Atmospheric deposition in the low-nutrient-low-chlorophyll (LNLC) ocean: effects on marine life today and in the future (BG/ACP inter-journal SI)(BG/ACP inter-journal SI) Editor(s): Christine Klaas, Cecile Guieu, Karine Desboeufs, Jan-Berend Stuut, Mark Moore, Paraskevi Pitta, Silvia Becagli, and Chiara Santinelli | ||||||||||||||||||||
Abstract | 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 µM). As a consequence, Km (Michaelis–Menten half-saturation constant) and Vm (maximum hydrolysis velocity) parameters were determined for both low- and high-affinity enzymes for alkaline phosphatase, aminopeptidase (LAP) and β-glucosidase (βGLU). Based on the constant derived from the high-LAP-affinity enzyme (0.025–1 µM substrate concentration range), in situ hydrolysis of N proteins contributed 48 % ± 30 % to the heterotrophic bacterial nitrogen demand within the epipelagic layers and 180 % ± 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 % ± 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 / βGLU enzymatic ratios and some of the depth-related trends differed between the use of high and low concentrations of fluorogenic substrates. |
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