Characterization of respiratory physiology in Lactococcus lactis for high-yield production of high-performance starter cultures
The aim of this work was to investigate the response of L. lactis to respiration-permissive conditions, to enable redesign and optimization of the batch production process. The process parameters were carefully chosen to mimic the industrial process. The effects of the specific growth rate on respiratory metabolism, energetics and cell quality were quantified using chemostat cultivations. Compared to anaerobic metabolism, the respiratory metabolism of L. lactis was remarkably flexible, and could be modulated by controlling the dilution rate. The lowest dilution rate supported full respiratory metabolism, whereas the higher dilution rates caused a shift towards respiro-fermentative metabolism. The inoculation procedures were investigated in detail to gain an understanding of the occurrence of lag phases after inoculation. It was found that the length of the lag phase in subsequent main cultures was related to galactose excretion in lactose-grown pre-cultures. Furthermore, based on lacS gene expression measurements in lactose-grown cultures, it is suggested that LacS is responsible for the galactose excretion as a galactose-lactose antiporter.
The quality of frozen and freeze-dried products was investigated and sensitivity to freeze-drying was found to be associated with the physiological state of the cells during cultivation. Cells harvested under respiration-permissive conditions in batch and chemostat cultivations at low dilution rate were less robust to freeze-drying, whereas higher dilution rates led to robust cells performing equally well or better than anaerobic cells.
The findings of this work underline the importance of systematically studying the combination of upstream and downstream aspects of production processes. The results indicate that by controlling the specific growth rate and the haemin concentration during the aerobic growth of L. lactis, not only higher biomass yields, but also better cell robustness, can be achieved.
Lactic acid bacteria
starter culture production
Chalmers, Biologi och bioteknik, Industriell bioteknik
Johanson, A., Olsson, L., Franzén, C. J. & Goel, A. Respiratory growth of Lactococcus lactis depends on hemin concentration and leads to impaired performance after freeze-drying
Johanson, A., Kovács J., Olsson, L., Goel, A., & Franzén, C. J. Hemin-activated respiration in Lactococcus lactis for high-yield biomass production depends on hemin concentrations
Respiratory Physiology of Lactococcus lactis in Chemostat Cultures and Its Effect on Cellular Robustness in Frozen and Freeze-Dried Starter Cultures
Applied and Environmental Microbiology,; Vol. 86(2020)
Artikel i vetenskaplig tidskrift
Presence of galactose in precultures induces lacS and leads to short lag phase in lactose-grown Lactococcus lactis cultures
Journal of Industrial Microbiology and Biotechnology,; Vol. 46(2019)p. 33-43
Artikel i vetenskaplig tidskrift
The bacteria used in starter cultures are often cultured in batch cultivation, after which the cells are separated and preserved, either by freezing or freeze-drying, before being sold to cheesemakers. The bacterial cells must remain viable and maintain a high acidification activity until they are added to the milk, which is why cellular robustness is important in achieving high performance starter cultures.
This research was carried out on the bacterium Lactococcus lactis, which is known for its high acidification performance. L. lactis has previously been regarded as a fermentative anaerobic microorganism, growing without oxygen, and producing mainly lactic acid. However, in the presence of oxygen and exogenous heme respiratory metabolism can be established, and the product profile is changed to acetate, acetoin and diacetyl, in addition to lactic acid. Respiration increases the biomass yield, leading to a high yield process.
The aim of this work was to investigate how cultivation conditions affect the physiology and robustness of L. lactis cells. Thereby gaining a better understanding, allowing the starter culture production process to be redesigned and optimized in such a way as to enable high-yield production of robust, high-performance starter cultures.
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4731
Lecture hall HA1, Hörsalsvägen 4, Chemistry building and via Zoom (Chalmers, Johanneberg campus). Please contact Gunilla Bankel firstname.lastname@example.org to obtain password for online participation.
Opponent: Professor Bas Teusink, System Biology Lab, AIMMS,Vrije Universitet Amsterdam, The Netherlands