Lactic acid bacteria-friend or foe? Lactic acid bacteria in the production of polysaccharides and fuel ethanol

Lactic acid bacteria (LAB) are generally considered to be beneficial microorganisms, as they have been widely used in the production of fermented foods and as probiotics. In this article we offer examples of research from our own laboratory that contrast the roles of LAB as either useful or undesirable agents. Specifically, we discuss the production of a valuable polysaccharide by Leuconostoc mesenteroides and the role of Lactobacillus sp. as contaminants of fuel ethanol production. Alternan is a glucan with a distinctive backbone structure of alternating α-(1,6) and α-(1,3) linkages produced by the LAB L. mesenteroides. In recent years, we have developed improved strains for production of alternan and novel derivatives, including a lower molecular weight form that more closely mimics gum arabic. Alternan oligosaccharides were produced using enzyme-catalyzed acceptor reactions and have potential as second generation prebiotics. This alternan technology led to the development of sucromalt, a low-glycemic index sweetener produced by Cargill that appears in the Glucerna line of diabetic foods. More recently, LAB have been investigated as microbial catalysts for production of fuels and chemicals from lignocellulosic biomass. LAB are well suited for ethanol production due to their ability to utilize a range of mixed substrates and their high tolerance to environmental ethanol concentrations. Nevertheless, these same characteristics also make LAB prolific contaminants of fuel ethanol fermentations, creating a costly problem for the ethanol industry. We have isolated bacterial contaminants from a variety of US fuel ethanol production facilities and determined their antibiotic susceptibility. These strains were used to develop a reliable cstucke fermentation model that will be useful in developing effective intervention strategies to control bacterial contamination in commercial fermentation cultures.