Engineering functionality of complex starter cultures

The use of starter cultures is an essential aspect in cheese manufacturing. Starter cultures may consist of single strains or mixtures of different strains and species of mainly lactic acid bacteria. An undefined mixture of different strains and species can be regarded as a complex ecosystem. Starter culture “Ur”, used for the production of Gouda cheese is an example of a complex starter culture and it contains 7 genetic lineages of Lactococcus lactis and 1 of Leuconostoc mesenteroides [1]. Complex ecosystems are known for their stability in composition, even during the process of back-slopping, where new milk is inoculated with whey from the previous batch. We set out to investigate the compositional stability of starter culture Ur during propagation at different temperatures. In addition, Ur was reconstituted from the 8 defined genetic lineages in 1:1 starting ratio. Propagation was carried out in fat free milk and the inoculated milk was incubated at 20°C, 25°C and 30°C. These temperatures were selected to possibly favor strains that have different optimum growth temperatures. After 28 transfers (~200 generations) the composition of Ur and the reconstituted mixtures was determined using qPCR with lineage specific primers. Sequential propagation of Ur in milk at different temperatures induced changes in the relative abundance of different genomic lineages, but none of the lineages were lost. We also demonstrated that reconstituted Ur, in comparison with original Ur, leads to a similar end-point composition after 28 transfers as Ur. This demonstrates the robustness of the original Ur culture and suggests interactions between the different lineages. 1. Erkus O, de Jager VC, Spus M, van Alen-Boerrigter IJ, van Rijswijck IM, Hazelwood L, Janssen PW, van Hijum SA, Kleerebezem M, Smid EJ: Multifactorial diversity sustains microbial community stability. ISME J 2013, 7:2126-2136.