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Towards sequential bioethanol and L-lactic acid co-generation

Cubas-Cano, E.; López-Gómez, J.P.; González‐Fernández, C.; Ballesteros, I.; Tomás‐Pejó, E. “Towards sequential bioethanol and L-lactic acid co-generation: Improving xylose conversion to L-lactic acid in presence of lignocellulosic ethanol with an evolved Bacillus coagulans” Renewable Energy, 2020, 153, 759-765.

The main aim of this work was to study the valorisation of lignocellulosic materials into multiple bio-based products. Lignocellulosic biomass is the cheapest, widest distributed and most abundant renewable carbon source in the world. In contrast to petrochemical refineries, biorefineries have emerged as a sustainable approach for the microbial conversion of sugars from lignocellulosic biomass into a spectrum of marketable bio‐based products and bioenergy. Glucose derived from cellulosic fraction of lignocellulose can be fermented into bioethanol using industrial yeasts. While these yeasts are not able to metabolise five-carbon sugars derived from hemicellulosic fraction, several bacteria can convert them into lactic acid, which present plenty of industrial applications.

In this work, an integrated sequential ethanol and L-lactic acid fermentation process has been implemented to valorise gardening residues. In the first stage, glucose fermentation of a gardening hydrolysate was carried out by Saccharomyces cerevisiae, producing 0.44 g g-1 of ethanol.  In the second stage, the resulting ethanol-rich medium was fermented by Bacillus coagulans to convert xylose into L-lactic acid. Since high ethanol concentrations can hinder bacterial growth and metabolism, an Adaptive Laboratory Evolution experiment was carried out to increase its ethanol tolerance. As a result, 0.89 g g-1 of lactic acid were obtained by the evolved bacteria, meaning 2.6-fold improvement in comparison with the parental strain. This novel approach can increase the valorisation of different sugars from lignocellulosic materials via ethanol and lactic acid sequential fermentation, making a great contribution to the implementation of biorefineries.

More information: Cristina González, Head of the Biotechnological Processes Unit cristina.gonzalez@imdea.org   

Event Date: 
Thursday, April 2, 2020