Genetically Engineered Lactobacilli for Technological and Functional Food Applications

Lactic acid bacteria (LAB) are Gram-positive microorganisms that produce lactic acid as a major product of their metabolism. Among them the genus Lactobacillus comprises a large heterogeneous group of low G+C DNA content, anaerobic and nonsporulating bacteria, that includes species widely used in the food industry. They play key roles in fermented dairy, meats and vegetables products. Due to their claimed health-promoting properties certain lactobacilli species are used as probiotics and they are commonly applied to dairy and functional foods products. Lactobacilli have a relatively simple fermentative metabolism focused to rapidly convert carbohydrates into lactic acid, and exhibited a limited biosynthetic capacity. In addition, several tools and strategies to manipulate them genetically are available. All those characteristics make lactobacilli specially suited for genetic engineering aimed to increase existing compounds or to produce novel metabolites of interest for the food industry. Regarding probiotic lactobacilli, through genetic manipulation, the health attributes of probiotic strains can be enhanced or new probiotic activities can be developed and additionally, an understanding of the underlying molecular mechanisms can be obtained. Here, we review metabolic engineering strategies in lactobacilli that have successfully been used to efficiently reroute sugar metabolism to compounds such as L-lactic acid, aroma compounds (acetoin, diacetyl), low-calorie sugars (mannitol, sorbitol) and exopolysaccharides. We will also describe strains of probiotic lactobacilli that have been developed to exploit their adherence and immunomodulatory properties, and to delivery proteins at the intestinal mucosa.