A combined physiological and proteomic approach to reveal lactic-acid-induced alterations in Lactobacillus casei Zhang and its mutant with enhanced lactic acid tolerance

Abstract

Lactobacillus casei has traditionally been recognized as a probiotic and frequently used as an adjunct culture in fermented dairy products, where acid stress is an environmental condition commonly encountered. In the present study, we carried out a comparative physiological and proteomic study to investigate lactic-acid-induced alterations in Lactobacillus casei Zhang (WT) and its acid-resistant mutant. Analysis of the physiological data showed that the mutant exhibited 33.8% higher glucose phosphoenolpyruvate:sugar phosphotransferase system activity and lower glycolytic pH compared with the WT under acidic conditions. In addition, significant differences were detected in both cells during acid stress between intracellular physiological state, including intracellular pH, H(+)-ATPase activity, and intracellular ATP pool. Comparison of the proteomic data based on 2D-DIGE and i-TRAQ indicated that acid stress invoked a global change in both strains. The mutant protected the cells against acid damage by regulating the expression of key proteins involved in cellular metabolism, DNA replication, RNA synthesis, translation, and some chaperones. Proteome results were validated by Lactobacillus casei displaying higher intracellular aspartate and arginine levels, and the survival at pH 3.3 was improved 1.36- and 2.10-fold by the addition of 50-mM aspartate and arginine, respectively. To our knowledge, this is the first demonstration that aspartate may be involved in acid tolerance in Lactobacillus casei. Results presented here may help us understand acid resistance mechanisms and help formulate new strategies to enhance the industrial applications of this species.

Differences in acid tolerance between Bifidobacterium breve BB8 and its acid-resistant derivative B. breve BB8dpH, revealed by RNA-sequencing and physiological analysis

“…5) also implied the reduction of lactate production and increase of acetate production, resulting in a higher acetate/lactate ratio in BB8dpH. The displacement of the bifid shunt toward acetate production could increase ATP production at the substrate level [30], and this could enhance the ability of cells to regulate the internal pH under acidic environments [28,31,32]. Therefore, the higher acid tolerance of BB8dpH might be related to the regulation of the expression of DEGs involved in acetate and lactate production.…”

“…Previous studies reported that enhancing the ability to transport and utilize carbohydrates as carbon sources could help cells withstand acidic environments in Lactobacillus casei and Bifidobacterium longum subsp. longum BBMN68 [7,28]. In the present study, the DEGs related to sugar ABC transporter systems were involved in the uptake of various carbohydrates such as glucose, arabinose, xylose and glycogen.…”

“…5) might imply the higher production of peptidoglycan as an important component of cell wall, and consequently strengthen cell wall structure. Wu et al [28] reported that strengthening cell wall structure could help cells protect against acidic environments. Thus, the higher expression of DEGs involved in peptidoglycan synthesis could be one of the reasons for the higher acid tolerance of BB8dpH.…”

Microbial production of lactic acid

“…casei showed greater PTS activity, greater H ? -ATPase activity and, at lower values of pH, maintained a higher intracellular pH than the wild-type, with a subsequent proteomic analysis demonstrating the complexity of pH tolerance (Wu et al 2012). The response of LAB to low pH involves surprisingly numerous genes or proteins (Rallu et al 2000;De Angelis et al 2001).…”

Dynamic Stresses of Lactic Acid Bacteria Associated to Fermentation Processes

“…Combined transcriptomic and proteomic analyses were used to evaluate the glucose-limited chemo-stat in Enterococcus faecalis V583 [129] or to study the effect of bile salts in the growth of L. casei [130]. A combined physiological and proteomic approach, instead, was followed to unravel lactic-acid-induced alterations in L. casei [131].…”