Dhr.drs. S. (Sander) Sieuwerts: ‘How lactic acid bacteria cooperate to make a good yoghurt'

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27 Oct 2009 13:30
Unit: Wageningen University
Location: Aula, building 362, Gen. Foulkesweg 1, Wageningen
Organisation: Wageningen University
Promotor: prof.dr. W.M. de Vos (Microbiology)
Co Promotor: Dr. J. van Hylckama Vlieg (Danone Research Center, Palaiseau, France)

 Yoghurt is made by fermenting bovine milk with the lactic acid bacteria Streptococcus thermophilus and Lactobacillus bulgaricus. These bacteria enhance each other’s growth by exchanging stimulatory components. However, it was not well known how that works. In this research the genes switched on or off upon mixing the bacteria were identified. This information was combined with a study after the evolution of the mixture and the development of a computer model that contains all reactions in the bacteria and their interactions. The cooperation between the bacteria appeared to be based on the exchange of amino acids and components necessary for the production of DNA and fatty acids, and on the production of long-chain sugars. The evolution study showed that it is possible to adapt a new combination of lactic acid bacteria leading to a mixture that performs better than the ones currently used in industry. This result and unravelling the interactions between the bacteria are very important for the proper application of prociotics in new products.
Title thesis: Analysis of molecular interactions between yoghurt bacteria by an integrated genomics approach.

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