Physiological and Transcriptional Response ofLactobacillus caseiATCC 334 to Acid Stress

Abstract

This study investigated features of the acid tolerance response (ATR) inLactobacillus casei is an aciduric, rod-shaped, facultatively heterofermentative lactic acid bacterium (LAB) that can be isolated from a variety of environments including raw and fermented milk and meat or plant products, as well as the oral, intestinal, and reproductive tracts of humans and animals (24). Like other LAB species, L. casei produces lactic acid as a major end product of carbohydrate fermentation during growth, and strains of L. casei are used as acid-producing starter cultures in the preparation of fermented foods, as health-enhancing probiotic cultures, and for the production of L(ϩ)-lactic acid (18,47,52). In each of these applications, the industrial performance of L. casei strains is dependent, in one way or another, on their acidurance.During fermentation, L. casei transports lactic acid outside the cell as lactate ion via an electrogenic proton-lactate symporter. As the pH of the medium (pH o ) decreases or the concentration of lactate increases, the concentration of protonated (undissociated) lactic acid in the medium also increases. The undissociated form of lactic acid is membrane soluble and thus can enter the cytoplasm by simple diffusion (27). Metabolically active bacteria maintain a pH gradient (⌬pH) where the intracellular pH (pH i ) is more alkaline than the pH o (4, 25), so diffusion of acid into the cytoplasm results in rapid dissociation and release of protons and anions inside the cell.

Optimisation of Cell Bioenergetics in Food-Associated Microorganisms

“…All of the metabolic reactions that result in the alkalisation of the cytosol of acidogenic organisms (such as those involved in the arginine deiminase (ADI) pathway, the citrate metabolism or else those involved in malolactic conversion) should be analysed in light of these novel findings. Indeed, and not surprisingly, all previous pathways act by subtracting protons from the cytoplasm and are strongly induced by an acidic environmental pH (Magni et al, 1999;Cotter & Hill, 2003;Broadbent et al, 2010). The conserved role of alkalising reactions across acidogenic bacteria is also supported by the data obtained for L. lactis IL1403-945 and S. pneumoniae SP292-945 in the presence of glucose and cellobiose as a carbon source (Arioli et al, 2010).…”

Global transcriptome response to ionic liquid by a tropical rain forest soil bacterium,Enterobacter lignolyticus

“…However, the increase in cyclopropane fatty acid production during [C 2 mim]Cl exposure demonstrates the distinct effect of ionic liquid on the bacterium. A number of studies using E. coli and lactobacilli have demonstrated that methylation of the cis-acyl chain double bond to form a cyclopropane ring plays a significant role in tolerance to acid, salt, butanol, and other stressors by reducing membrane fluidity and decreasing permeability (50)(51)(52)(53)(54). It is probable that cyclopropane fatty acid production plays a similar role in [C 2 mim]Cl tolerance by stabilizing the cell membrane.…”

Stress Physiology of Lactic Acid Bacteria

“…casei ATCC 334 and Lb. johnsonii NCC 533 showed a significant increase in the ratio of saturated to unsaturated membrane fatty acids (122,467). In the latter strain, the membrane fatty acid composition (and in particular the saturation level) is associated with changes in cell survival during heat or acid shock.…”

“…lactis (121) and Lb. casei (122) and in a number of stress conditions in E. faecalis (123,124), S. mutans (125), and S. pneumoniae (126). A number of studies have shown that RSH is mainly involved in the classical SR, whereas the small synthetases may play different roles.…”