M.I. (Marieke) Pastink: “Bacteria with taste: a comparison”

Lactic Acid Bacteria have been used for centuries for the production of fermented foods such as cheese and yoghurt. These bacteria not only produce lactic acid during growth, but also other, interesting metabolites such as vitamins and flavours. Some of these flavours can be generated during amino acid degradation. This thesis describes a comparative study of amino acid metabolism of three lactic acid bacteria. For this comparative approach, we used both experiments and in silico models. This study showed that  Streptococcus thermophilus LMG18311, a so-called ‘yoghurt strain’ only needs 2 amino acids in the growth medium and is able to produce different flavours. Two other studied lactic acid bacteria, Lactococcus lactis MG1363 and Lactobacillus plantarum WCFS1, need respectively 6 and 11 amino acids in the medium and produce less flavours than S. thermophilus. The comparative study also showed the absence of a complete pentose phosphate pathway in S. thermophilus. This pathway is important for the generation of NADPH, a co-factor that is needed for the biosynthesis of different compounds.

The comparative genomics approach presented in this thesis can be used to understand the amino acid metabolism of different lactic acid bacteria and their potential to produce flavors under different conditions. Finally, it can be applied for optimization of industrial fermentations.