PhD study trip

Population dynamics in undefined mixed starter culture - the role of bacteriophages

Starter cultures are used in dairy industry applications like cheese or yoghurt production [1]. Steering the functionality of the starters has significant industrial relevance.

Although, to be able to have an impact on the final product, by influencing the performance of microbes, the fundamentals of their behavior in milk on the population and strain level need to be investigated.


By the exploring of the genetic and phenotypic characteristics of the bacteria found in cheese the knowledge about the drivers for heterogeneity in the culture will be deepened. Due to the insight in the heterogeneity the possible tools for steering the functionality will be developed.


The research approach is mainly based on the adaptive evolution experiments. Sequential propagation of starter culture and its isolates [2] in milk will unravel the character of changes in population dynamics. To follow this phenomena the genome-based methods are being used, such as QPCR. Furthermore, mild stresses will be used to direct the evolution of particular strains and improve the general culture robustness.

Future research

The near future research contains further adaptive evolution experiments with predefined mixtures of strains isolates, including protease positive and protease negative types. Bacteriophages, which were previously isolated from the undefined starter, will be introduced to the mixture to investigate their influence on population dynamics.


Bacteriophages have an impact on the culture by predating on sensitive variants and at the same time favour the resistant types. Protease activity has an effect on the population dynamics in the culture.


1.  Sieuwerts, S., Analysis of molecular interactions between yoghurt bacteria by an integrated genomics approach, in Wageningen University, Department of Microbiology. 2009, Wageningen University: Wageningen.

2.  Kutahya, O., C-1001 TIFN Project, unpublished data.