Lactobacillus casei combats acid stress by maintaining cell membrane functionality

Abstract

Lactobacillus casei strains have traditionally been recognized as probiotics and frequently used as adjunct culture in fermented dairy products where lactic acid stress is a frequently encountered environmental condition. We have investigated the effect of lactic acid stress on the cell membrane of L. casei Zhang [wild type (WT)] and its acid-resistant mutant Lbz-2. Both strains were grown under glucose-limiting conditions in chemostats; following challenge by low pH, the cell membrane stress responses were investigated. In response to acid stress, cell membrane fluidity decreased and its fatty acid composition changed to reduce the damage caused by lactic acid. Compared with the WT, the acid-resistant mutant exhibited numerous survival advantages, such as higher membrane fluidity, higher proportions of unsaturated fatty acids, and higher mean chain length. In addition, cell integrity analysis showed that the mutant maintained a more intact cellular structure and lower membrane permeability after environmental acidification. These results indicate that alteration in membrane fluidity, fatty acid distribution, and cell integrity are common mechanisms utilized by L. casei to withstand severe acidification and to reduce the deleterious effect of lactic acid on the cell membrane. This detailed comparison of cell membrane responses between the WT and mutant add to our knowledge of the acid stress adaptation and thus enable new strategies to be developed aimed at improving the industrial performance of this species under acid stress.

Metabolism of Fructooligosaccharides in Lactobacillus plantarum ST-III via Differential Gene Transcription and Alteration of Cell Membrane Fluidity

“…Shorter chains have been reported to be unable to span the bilayer or form hydrophobic interactions with other lipids and proteins. As a result, the fluidity of the bilayer was increased due to the motion of the free acyl chain ends (16,41). Therefore, the decreased carbon chain length contributed to the increase in cell membrane fluidity, which was in agreement with our results for fluorescence anisotropy detected by the DPH probe.…”

“…Lactic acid bacteria (LAB), a group of bacteria widely employed in the food and pharmaceutical industries, may encounter various stress conditions during industrial processes or survival in the GIT. Several studies have suggested that the regulation of membrane status influences the survival of LAB cells under stress conditions, such as oxidative, heat, cold, acid, and osmotic stresses (10,16,17). However, the responses of the cellular membrane to alterations in the carbon source have not been described for LAB.…”

Genetic and Physiological Responses of Bifidobacterium animalis subsp. lactis to Hydrogen Peroxide Stress

“…The increase in intrinsic H 2 O 2 resistance could be associated with the higher percentage of cyclic fatty acids in the membrane (47,48). Previous studies have shown that in response to low pH and osmotic stress, cells modify their membranes through chain length, saturation, and cyclopropanation of fatty acids, which alters the transition temperature of the membrane and makes it less permeable to organic acids and salts (44,45,49). More importantly, cyclopropanation decreases the susceptibility of the cell membrane to lipid peroxidation by stabilizing the unsaturated bond through addition of a methyl group (50).…”

Med15B Regulates Acid Stress Response and Tolerance in Candida glabrata by Altering Membrane Lipid Composition

“…Fifty milligrams of dried cells was resuspended in an NaOH-methanol-distilled water solution (3:10:10, wt/vol/vol). The sample saponification and methylation and extraction of total fatty acids were carried out as described previously (54). Samples were analyzed by gas chromatography (GC) with a polyethylene glycol capillary column eluted at a flow rate of 29.6 ml/min as described previously (55).…”