BIOTECHNOLOGY OF MICROORGANISMS INVOLVED IN DAIRY FERMENTATIONS

The final goal of our research group is the development of fermented food products with increased nutritional value. Our work is focused on manipulation of food microorganisms, such as Lactic Acid Bacteria and Propionic Acid Bacteria. A rational approach for strain manipulation can only be reliably established with knowledge of metabolic networks and regulatory mechanisms of the organism.

NMR analysis coupled to isotopic labelling is a powerful non-invasive technique in metabolic studies. Our approach involves in vivo 13C and 31P-NMR analysis to characterize the metabolism of wild-type and genetically modified strains, after the addition of 13C-labelled substrate. The major advantage of this technique is the ability to determine time course intracellular metabolites directly in living cells.

Efficient genetic strategies to improve microorganisms for our benefit can only be achieved through a deep understanding of metabolic networks and their inter-relationships. A complementary line of work in our group comprises the modulation of central metabolism in Lactic Acid Bacteria. This approach is based on the analysis of data from NMR, in vitro determination of metabolites and determination of key-enzymes activities. Due to the convoluted interdependency of metabolic networks, mathematical modelling is extremely relevant in the context of metabolic engineering. The experimental data are used as input for construction of metabolic models, in collaboration with the Biomathematics group at ITQB.

PRODUCTION OF HEALTHIER FERMENTED FOOD PRODUCTS

Fermented food products with increased nutritional value can be obtained either by increased production or removal of specific compounds. Our group employs both approaches by developing research projects that involve metabolic engineering of dairy bacteria.

Efficient conversion of glucose or lactose to other sweeteners, such as mannitol and trehalose, is studied by metabolic engineering of Lactococcus lactis (mannitol) and Propionibacterium freudenreichii (trehalose) strains. These studies contribute to the increase of mannitol and trehalose levels in dairy products.

In most fermented milks and other dairy drinks, the milk sugar lactose is only partly fermented by the starter bacteria. This poses problems for people who suffer from lactose-intolerance. The improvement of lactose utilization by Lactococcus lactis represents another important research line of our group. An analogous strategy is used for enhancement of galactose consumption by starter bacteria (L. lactis) and subsequent removal from dairy products. Presence of high amounts of galactose is very undesirable because its consumption, in combination with alcohol, can create serious health problems in certain individuals.

The carboxylic acids and amino acids fermentation by decarboxylation pathways are extremely important activities both in a positive and negative manner, depending on the particular substrate and fermentation process. The overall goal of our group in this field is to exploit decarboxylation pathways in LAB to develop safe and optimized food technologies. The specific objective is to use the in vivo NMR techniques to characterize the interface between central metabolism and decarboxylation pathways in genetically modified strains in order to obtain reliable directives for further improvement of industrial strains.

STUDIES OF LACTIC ACID BACTERIA CENTRAL METABOLISM

Lactic Acid Bacteria play a key role in the production of fermented dairy products. There is an increasing demand for industrial strains tailored for the production of metabolites that benefit human health by improvement of the nutritional value of food products. The main purpose of this research line is to take advantage of global approaches to characterize central metabolism and regulatory networks in Lactococcus lactis. The ultimate goal is the achievement of a mathematical representation that can be used to anticipate efficient metabolic engineering strategies that allow the construction of strains with desired metabolic traits. The objective requires integrating in the metabolic model the regulatory circuitry that orchestrates gene expression, which is a very recent tentative pursuit.