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https://doi.org/10.5194/bg-2020-253
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2020-253
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  17 Aug 2020

17 Aug 2020

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A revised version of this preprint is currently under review for the journal BG.

Spatial patterns of biphasic ectoenzymatic kinetics related to biogeochemical properties in the Mediterranean Sea

France Van Wambeke1, Elvira Pulido1, Julie Dinasquet2,3, Kahina Djaoudi1,4, Anja Engel5, Marc Garel1, Sophie Guasco1, Sandra Nunige1, Vincent Taillandier6, Birthe Zäncker6,7, and Christian Tamburini1 France Van Wambeke et al.
  • 1Aix-Marseille Université, CNRS/INSU, Université de Toulon, IRD, Mediterranean Institute of Oceanography (MIO) UM 110, 13288, Marseille, France
  • 2Marine Biology Research Division, Scripps Institution of Oceanography, UCSD, La Jolla, USA
  • 3Sorbonne Universités, UPMC University Paris 6, Laboratoire d'Océanographie Microbienne (LOMIC), Observatoire Océanologique, 66650, Banyuls/mer
  • 4Molecular and Cellular Biology, The University of Arizona, Tucson, USA
  • 5GEOMAR – Helmholtz-Centre for Ocean Research, Kiel, Germany
  • 6CNRS, Sorbonne Universités, Laboratoire d'Océanographie de Villefranche (LOV), UMR7093, 06230 Villefranche-sur-Mer, France
  • 7The Marine Biological Association of the UK, Plymouth, United Kingdom

Abstract. Prokaryotic ectoenzymatic activity, abundance and heterotrophic production were determined in the Mediterranean Sea, within the epipelagic and the upper part of the mesopelagic layers. The Michaelis-Menten kinetics were assessed, using a range of low (0.025 to 1 µM) and high (0.025 to 50 µM) concentrations of fluorogenic substrates. Thus, Km and Vm parameters were determined for both low and high affinity systems for alkaline phosphatase (AP), aminopeptidase (LAP) and β-glucosidase (βGLU). Based on the constant derived from the high AP affinity system, in-situ hydrolysis rates of N-protein contributed of 48 % ± 30 % for the heterotrophic prokaryotic nitrogen demand within epipelagic waters and of 180 % ± 154 % within deeper layers. LAP hydrolysis rate was higher than bacterial N demand only within the deeper layer, and only based on the high affinity system. Although ectoenzymatic hydrolysis contribution to heterotrophic prokaryotic need was high in terms of N, but low in terms of C. Based on a 10 % bacterial growth efficiency, the cumulative hydrolysis rates of C-proteins and C-polysaccharides contributed to a small part of the heterotrophic prokaryotic carbon demand, on average 2.5 % ± 1.3 % in the epipelagic layers. This study notably points out the biases in current and past interpretation of the relative activities differences among the 3 tested enzymes, in regard to the choice of added concentrations of fluorogenic substrates. In particular, enzymatic ratios LAP/βGLU, as well as some trends with depth, were different considering activities resulting from the high or the low affinity system.

France Van Wambeke et al.

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France Van Wambeke et al.

France Van Wambeke et al.

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Short summary
The Michaelis-Menten kinetics of low and high affinity systems were determined for alkaline phosphatase, aminopeptidase and β-glucosidase in the Mediterranean Sea. Although ectoenzymatic hydrolysis contribution to heterotrophic prokaryotic needs was high in terms of N, it was low in terms of C. This study points out the biases in interpretation of the relative differences of activities among the 3 tested enzymes, in regard to the choice of added concentrations of fluorogenic substrates.
The Michaelis-Menten kinetics of low and high affinity systems were determined for alkaline...
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