A low membrane lipid phase transition temperature is associated with a high cryotolerance of Lactobacillus delbrueckii subspecies bulgaricus CFL1

Abstract

The mechanisms of cellular damage that lactic acid bacteria incur during freeze-thaw processes have not been elucidated to date. Fourier transform infrared spectroscopy was used to investigate in situ the lipid phase transition behavior of the membrane of Lactobacillus delbrueckii ssp. bulgaricus CFL1 cells during the freeze-thaw process. Our objective was to relate the lipid membrane behavior to membrane integrity losses during freezing and to cell-freezing resistance. Cells were produced by using 2 different culture media: de Man, Rogosa, and Sharpe (MRS) broth (complex medium) or mild whey-based medium (minimal medium commonly used in the dairy industry), to obtain different membrane lipid compositions corresponding to different recovery rates of cell viability and functionality after freezing. The lipid membrane behavior studied by Fourier transform infrared spectroscopy was found to be different according to the cell lipid composition and cryotolerance. Freeze-resistant cells, exhibiting a higher content of unsaturated and cyclic fatty acids, presented a lower lipid phase transition temperature (Ts) during freezing (Ts=-8°C), occurring within the same temperature range as the ice nucleation, than freeze-sensitive cells (Ts=+22°C). A subzero value of lipid phase transition allowed the maintenance of the cell membrane in a relatively fluid state during freezing, thus facilitating water flux from the cell and the concomitant volume reduction following ice formation in the extracellular medium. In addition, the lipid phase transition of freeze-resistant cells occurred within a short temperature range, which could be ascribed to a reduced number of fatty acids, representing more than 80% of the total. This short lipid phase transition could be associated with a limited phenomenon of lateral phase separation and membrane permeabilization. This work highlights that membrane phase transitions occurring during freeze-thawing play a fundamental role in the cryotolerance of Lb. delbrueckii ssp. bulgaricus CFL1 cells.

Assessment of the Potential of Lactic Acid Bacteria as Dried Starter Culture for Cereal Fermentation

“…Significant loss in viability of Lactobacillus delbrueckii ssp. bulgaricus CFL1 after freeze thawing in MRS broth was reported [8]. This difference in cell viability between strains was linked to the intrinsic resistance of the strain, the initial concentration, growth conditions and possibly the elimination of a large part of the sensitive population during the freezing step [9].…”

Cyclopropanation of unsaturated fatty acids and membrane rigidification improve the freeze-drying resistance of Lactococcus lactis subsp. lactis TOMSC161

“…When cells are exposed to changes in culture conditions during fermentation (temperature, pH, pressure, oxygen, nutrients, and ethanol), they modulate their membrane composition in order to maintain the lipid bilayer in the liquid crystalline lamellar phase and, more precisely, to maintain an optimal level of fluidity within the lipid bilayer (Johnsson et al 1995;Drici-Cachon et al 1996;Guillot et al 2000;Teixeira et al 2002;Gautier et al 2013). This level of fluidity is, in fact, required to preserve cellular functions that take place at the membrane level (solute transport and diffusion, energy transduction, cellular growth, and other metabolic functions).…”

UvrA expression of Lactococcus lactis NZ9000 improve multiple stresses tolerance and fermentation of lactic acid against salt stress

“…The decrease of ATP with increase of temperature resulted in the decrease of specific growth rate. Temperature and pH contribute to cell permeability, enzymes activities and amino acid metabolic pathway (Gautier et al 2013). In Escherichia coli the instigation of heat-shock resistance was shown to be dependent on the products of the uvrA gene.…”