Better yoghurt through cooperating bacteria
NIZO has developed a genome-based model for rational optimization of existing mixed culture fermentations. In addition, new and more efficient mixed cultures can be developed by means of rational improvement but also through evolution of these cultures.
These are the results of research carried out by Sander Sieuwerts who will defend his thesis on this topic on October 27th.
Yoghurt is made by fermenting milk with the lactic acid bacteria Streptococcus thermophilus and Lactobacillus bulgaricus. The bacteria promote each others growth because of exchange of stimulating compounds. Until now, such microbial interactions were often poorly understood. In the thesis “Analysis of molecular interactions between yoghurt bacteria by an integrated genomics approach“ by Sander Sieuwerts, the interactions between yoghurt bacteria are revealed. For the dairy industry but also for companies fermenting plant products, unraveling these interactions is highly interesting. Optimisation of the interactions can result in a more efficient fermentation. Furthermore, the information can be used for product innovation such as new combinations of cultures for new flavours, textures or health properties.
The study consists of a combined approach of screening for culture growth, gene-expression analysis, experimental evolution and modeling. With the gene-expression analysis, genes have been identified that are either switched-on or switched-off when the two bacteria are brought together. The information emanating from these studies was combined with a study to the evolution of the mixed culture and the development of a genome-based computer model that describes all reactions inside the bacteria as well as their interactions. In this way, Sieuwerts could prove that the interaction provides a significant advantage for both bacteria, that is, their yield of biomass on lactose was about 50% higher in a mixed culture.
The evolution study showed that it is possible for a new combination of lactic acid bacteria to adjust to each other, resulting in faster and more efficient fermentation than the combinations currently used by industry. ‘Only 1000 generations of breeding together was sufficient to change a relatively poorly growing mixed culture into one that is comparable to a commercially used culture’ explains Sieuwerts. In the near future the model can be used to predict interactions in other combinations of bacteria.
The research for this thesis was carried out in the framework of TI Food and Nutrition. On October 27th Sander Sieuwerts will defend his thesis at the Wageningen University. Promotor is Prof. Dr. Willem de Vos and co-promotor is Dr. Johan van Hylckama Vlieg.