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Front. Microbiol. | doi: 10.3389/fmicb.2018.00291

Mapping the physiological response of Oenococcus oeni to ethanol stress using an extended Genome-Scale Metabolic Model

  • 1Department of Chemical and Bioprocess Engineering, School of Engineering, Pontificia Universidad Católica de Chile, Chile
  • 2Faculty of Physical and Mathematical Sciences, Universidad de Chile, Chile
  • 3Universidad de Chile, Chile

The effect of ethanol on the metabolism of Oenococcus oeni, the bacterium responsible for the malolactic fermentation of wine, is still scarcely understood. Here, we characterized the global metabolic response in O. oeni to increasing ethanol contents, ranging from 0 to 12% (v/v). We first optimized a wine-like, defined culture medium, MaxOeno, to allow sufficient bacterial growth to be able to quantitate different metabolites in batch cultures of O. oeni. Then, taking advantage of the recently reconstructed genome-scale metabolic model iSM454 for O. oeni PSU-1 and the resulting experimental data, we determined the redistribution of intracellular metabolic fluxes, under the different ethanol conditions.
Four growth phases were clearly identified during the batch cultivation of O. oeni PSU-1 strain, according to the temporal consumption of malic and citric acids, sugar and aminoacids uptake, and biosynthesis rates of metabolic products – biomass, erythritol, mannitol and acetic acid, among others.

We showed that, under increasing ethanol conditions, O. oeni favors anabolic reactions related with cell maintenance, as the requirements of NAD(P)+ and ATP increased with ethanol content. Specifically, cultures containing 9 and 12% ethanol required 10 and 17 times more NGAM (non-growth associated maintenance ATP) during phase I, respectively, than cultures without ethanol. Malolactic fermentation and citric acid consumption are vital at high ethanol concentrations, as they are the main source for proton extrusion, allowing higher ATP production by F0F1-ATPase, the main route of ATP synthesis under these conditions. Mannitol and erythritol synthesis are the main sources of NAD(P)+, countervailing for 51-57% of its usage, as predicted by the model. Finally, cysteine shows the fastest specific consumption rate among the amino acids, confirming its key role for bacterial survival under ethanol stress. As a whole, this study provides a global insight into how ethanol content exerts a differential physiological response in O. oeni PSU-1 strain. It will help to design better strategies of nutrient addition to achieve a successful malolactic fermentation of wine.

Keywords: physiological ethanol response, wine-like defined culture medium, malolactic fermentation, Lactic acid bacteria, Oenococcus oeni, Genome-scale metabolic model

Received: 22 Oct 2017; Accepted: 07 Feb 2018.

Edited by:

Vittorio Capozzi, University of Foggia, Italy

Reviewed by:

Sonia Cortassa, National Institutes of Health (NIH), United States
Hugo Campbell-Sills, Institut des Sciences de la Vigne et du Vin (ISVV), France  

Copyright: © 2018 Contreras, Ribbeck, Gutiérrez, Cañón, Mendoza and Agosin. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: PhD. Eduardo Agosin, Pontificia Universidad Católica de Chile, Department of Chemical and Bioprocess Engineering, School of Engineering, Av. Vicuña Mackenna 4860, Macul, Santiago, 7820436, Región Metropolitana, Chile, agosin@ing.puc.cl