Alternative strategies for lignocellulose fermentation through lactic acid bacteria: state-of-the-art and perspectives

Abstract

Lactic acid bacteria (LAB) have a long history in industrial processes as food starters and biocontrol agents, but also as producers of high-value compounds. Lactic acid, their main product, is among the most requested chemicals owing to its multiple applications including synthesis of biodegradable plastic polymers. Moreover, LAB are attracting candidates for production of ethanol, polyhydroalkanoates, sweeteners, exopolysaccharides, etc.. LAB generally have complex nutritional requirements. Moreover, they cannot directly ferment inexpensive feedstocks such as lignocellulose. This significantly increases the cost of LAB fermentation and hinders its application to produce high-volume low-cost chemicals. Different strategies have been explored to extend LAB fermentation to lignocellulosic biomass. Fermentation of lignocellulose hydrolysates by LAB has most often been reported and is the most mature technology. However, current economic constraints of this strategy have driven research for other alternative approaches. Co-cultivation of LAB with native cellulolytic microorganisms may allow to reduce the high cost of exogenous-cellulase supplementation. Special attention will be given here to construction of recombinant cellulolytic LAB by metabolic engineering which may generate strains able to directly ferment plant biomass. The present review will illustrate the state-of-the-art of these strategies and perspectives towards their application to industrial 2^nd generation biorefinery processes.