Influence of the growth at high osmolality on the lipid composition, water permeability and osmotic response of Lactobacillus bulgaricus

doi:10.1016/j.abb.2005.09.004

Archives of Biochemistry and Biophysics

Volume 443, Issues 1–2, 15 November 2005, Pages 66-73

https://doi.org/10.1016/j.abb.2005.09.004 Get rights and content

Abstract

Changes in water permeability and membrane packing were measured in cells of Lactobacillus bulgaricus and in vesicles prepared with lipids extracted from them. The osmotic response of whole cells and vesicles is compared with the one of bacteria grown in a high osmolal medium. Both bacteria and vesicles, behave as osmometers. This means that the volume decrease is promoted by the outflow of water, driven by the NaCl concentration difference, arguing that neither Na⁺ nor Cl⁻ permeates the cell or the lipid membrane in these conditions. Therefore, the volume changes can be correlated with the rate of water permeation across the cell or the vesicle membranes. The permeation of water was analyzed as a function of the lipid species by measuring the volume changes and the saturation ratio of the lipids. To put into relevance the membrane processes, the permeation properties of lipid vesicles prepared with lipids extracted from bacteria grown in normal and high osmolality conditions were also analyzed. The permeation response was correlated with the physical properties of the membrane of whole cells and vesicles, by means of fluorescence anisotropy of diphenyl hexatriene (DPH). The modifications in membrane properties are related with the changes in the membrane composition triggered by the growth in a high osmolal medium. The changes appear related to an increase in the sugar content of the whole pool of lipids and in the saturated fatty acid residues.

Section snippets

Bacterial strains and growth conditions

Lactobacillus delbrueckii subsp. bulgaricus CIDCA 333 was isolated from a fermented product [22]. The strain was maintained frozen at −80 °C in 120 g L⁻¹ non-fat milk solids.

Cultures were grown in the following media: MRS broth (De Man et al. [20]) and MRS added with polyethylene glycol (PM 10000) (Sigma Aldrich, USA) to reach a final concentration of 2.5 g in 100 ml of the growth media. The final concentration of PEG was expressed in osmolality. Cultures in the stationary phase were harvested by

Results

Fig. 1 displays the typical curves of volume decrease induced by the hyperosmotic shock performed by the mixing of cells (Fig. 1A) or vesicles (Fig. 1B) with different NaCl concentrations.

The main differences can be summarized as follows. When bacteria were grown in MRS-PEG, a much lower decrease of volume was observed for the two osmotic gradient tested.

The same qualitative response was obtained with vesicles prepared with lipids from bacteria grown in MRS or in MRS-PEG (Fig. 1B). However, the

Discussion

Table 1 shows the slope of the volume change vs osmotic pressure (Figs. 3A and B). The decrease of volume is much more important in vesicles prepared with lipids of bacteria grown, both in MRS or MRS-PEG media. In whole bacteria, the decrease in permeability is congruent with the increase in anisotropy, which is parallel to a net increase in the sugar content and to the saturated fatty acyl residues in the phospholipid membrane.

The values of the slopes are much higher in vesicles than in cells (

Conclusions

In this work, the addition of a high osmolality agent (PEG) to the growth medium induced changes on the permeability of both whole cells and vesicles of lipids extracted from them. The behavior of cells and vesicles as osmometers was also demonstrated by measuring the volume decrease promoted by the outflow of water (driven by the NaCl concentration difference). This permeation of water across the membrane of both whole cells and vesicles of lipids was correlated with physical properties of the

Acknowledgments

This work was supported with funds from Agencia Nacional de Promoción Científica y Tecnológica, Grant PICT 06047 and PICT 13080. E.A.D. and A.G.Z. are members of the research career of CONICET (National Research Council, Argentina). E.E.T. is a fellow of the University of Buenos Aires.

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Influence of the growth at high osmolality on the lipid composition, water permeability and osmotic response of Lactobacillus bulgaricus

Abstract

Section snippets

Bacterial strains and growth conditions

Results

Discussion

Conclusions

Acknowledgments

Cryobiology

J. Biochem. Biophys. Methods

Arch. Biochem. Biophys.

Arch. Biochem. Biophys.

Arch. Biochem. Biophys.

Biochim. Biophys. Acta

Chem. Phys. Lipids

Biophys. Chem.

J. Dairy Sci.

J. Biol. Chem.

J. Appl. Microbiol.

Microbiol. Rev.

Biotechnol. Prog.

J. Dairy Res.

Microbiol. Mol. Biol. Rev.

Trends Microbiol.

Cryobiology