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

Type Article
Date 2021
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
Source Biogeosciences (1726-4189) (Copernicus GmbH), 2021 , Vol. 18 , N. 7 , P. 2301-2323
DOI 10.5194/bg-18-2301-2021
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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Van Wambeke France, Pulido Elvira, Catala Philippe, Dinasquet Julie, Djaoudi Kahina, Engel Anja, Garel Marc, Guasco Sophie, Barbara Marie, Nunige Sandra, Taillandier Vincent, Zancker Birthe, Tamburini Christian (2021). Spatial patterns of ectoenzymatic kinetics in relation to biogeochemical properties in the Mediterranean Sea and the concentration of the fluorogenic substrate used. Biogeosciences, 18(7), 2301-2323. Publisher's official version : https://doi.org/10.5194/bg-18-2301-2021 , Open Access version : https://archimer.ifremer.fr/doc/00642/75452/