Towards lactic acid bacteria-based biorefineries

Lactic acid bacteria (LAB) have been used in industrial applications mainly as starters for food fermentation (e.g., dairy products, wine and fermented vegetable and meats) or as biocontrol agents or as probiotics. However, LABpossess several characteristics that renderthem among the most promising candidates for use in future biorefineries in converting plant-derived biomasses – either from dedicated crops or from municipal/industrial solidwastes – into high-value products (e.g., food additives, nutraceuticals, biodegradable plastics and biofuels). Lactic acid (LA), their main fermentation product, is currently one of the most requested “building blocks” by the chemical industry,owing to the potential of its polymeric derivatives [i.e., polylactides (PLA)] for use as a general-purpose biodegradable and biocompatible plastic alternative to polymers derived from petrochemicals. LA is but one of many high-value compounds which can be produced by LAB fermentation, which also include biofuels (e.g., ethanol and butanol), biodegradable plastic polymers (i.e., polyhydroxyalkanoates, PHA), derivatives such asexopolysaccharides, which improve the rheological properties of food,sweeteners (e.g., mannitol and alanine),antimicrobial molecules (i.e., bacteriocins), molecules with human health-promoting and/or nutraceutical properties [e.g.,seleno metabolites, -aminobutyric acid (GABA), short chain fatty acids andconjugated linoleic acids]. Furthermore, several LAB strains have ascertained probiotic properties, so that their biomass itself can actually be considereda high-value fermentation product. The present contributionaims to provide an extensive overview of the main current industrial applications ofLAB and future perspectivesconcerning their utilization in biorefineries for converting waste biomass by fermentation. Examples will be given where high-value molecule production by LAB has been improved by either fermentation or metabolic engineering through genetic manipulation techniques. Furthermore, strategies will be described in detail for developing LAB strains with broader substrate metabolization capacity to ferment cheaper biomass,such as starch or lignocellulose, thereby enabling such recombinant LAB strains to be used in third generation biorefineries (i.e., consolidated bioprocessingof plant-derived biomass).