Metabolic models for rational improvement of lactic acid bacteria as cell factories

Lactic acid bacteria (LAB) are microbes that are used all over the world in a variety of fermentations. Beside their most important application, which is undoubtedly in the dairy industry, LAB are also applied at an industrial scale in the fermentation of other food-raw materials like meat and vegetables. LAB have a relatively simple carbon and energy metabolism which is characterized by the rapid glycolytic conversion of sugars into lactic acid. Many examples of successful metabolic engineering approaches in LAB focus on re-routing of the pyruvate metabolism. Recently, LAB have also been used for the engineering of complex biosynthetic pathways leading to the production of valuable metabolites with health benefits for the consumers (Hugenholtz and Smid 2002). Engineering complex biosynthetic pathways such as for vitamin or polysaccharide biosynthesis, often leads to unexpected phenotypes which can only be understood if genome-wide metabolic models of the microorganism are available. Here we describe the construction of metabolic models of Lactobacillus plantarum based on the availability of genome sequence information. After prediction of gene function, we have focused on the development and improvement of methods and tools to go from genome sequence to gene annotation, to pathway reconstruction and to prediction of phenotype through metabolic models. We have set up different bioinformatics tools, including web-interfaced databases and simulation software. This paper describes some of these tools, and how they are used and combined with experimental data to arrive at a model of the metabolic network of L. plantarum. The use of these types of models and the type of questions that can be addressed will be discussed.