Characterisation of respiratory physiology and development of stress tolerance in Lactococccus lactis for high yield production of robust high-performance starter cultures

Research Project, 2014 – 2018

The aim of the project is to understand the cellular behavior, i.e. the microbial physiology, at respiratory, fermentative and respiro-fermentative conditions and how the physiology is related to cellular robustness.

Lactic Acid Bacteria (LAB) are used worldwide within dairy industries as starter cultures in industrial production of various fermented foods. Manufacturing control and reproducibility is crucial for dairy companies why starter cultures must have known and guaranteed fermentation performance. The quality of starter cultures is directly linked to the conditions the cells have been exposed to throughout production.
Lactococcus lactis, a common LAB used in hard and semi-hard cheese production, has previously been regarded only as an anaerobic fermentative microorganism producing mainly lactic acid. However, respiratory metabolism can be established in the presence of oxygen if cells are provided with exogenous heme. The metabolic product profile changes to acetate, acetoin and diacetyl production, beside lactic acid. Furthermore, respiration results in increased cell yield compared to anaerobic conditions and it affects the cellular robustness. It is not yet understood how and why the metabolic and physiological differences impact the cellular robustness.

In this project we want to identify the metabolic and physiological differences between fermentative, respiro-fermentative, and respiratory metabolism in batch and continuous cultivations by using metabolomics and cellular activity after freezing and freeze-drying. The long-term goal is to redesign and optimize the batch production process with high final cell biomass concentration and excellent cellular robustness.