Rerouting of pyruvate metabolism during acid adaptation in Lactobacillus bulgaricus

Abstract

Lactic acid bacteria (LAB) gradually acidify their environment through the conversion of pyruvate to lactate, an essential process to regenerate NAD(+) used during glycolysis. A clear demonstration of acidification can be found in yogurt, the product of milk fermentation by the LAB Lactobacillus delbrueckii ssp. bulgaricus (L. bulgaricus) and Streptococcus thermophilus, where the pH falls to 4.2. Acid adaptation therefore plays an important role in the physiology of LAB. Here we present the results of a proteomic approach to reveal cellular changes associated with acid adaptation in L. bulgaricus. These results were complemented with transcription data for selected genes to show three major effects: (i) induction of the chaperones GroES, GroEL, HrcA, GrpE, DnaK, DnaJ, ClpE, ClpP, and ClpL, and the repression of ClpC; (ii) induction of genes involved in the biosynthesis of fatty acids (fabH, accC, fabI); (iii) repression of genes involved in the mevalonate pathway of isoprenoid synthesis (mvaC, mvaS). Together with changes in the expression of other genes from the local metabolic network, these results for the first time show a coherent picture of changes in gene expression expected to result in a rerouting of pyruvate metabolism to favor fatty acid biosynthesis, and thereby affect membrane fluidity.

Characterization of Two Component Systems of Lactobacillus casei BL23 and their involvement in stress response

“…The same change in pyruvate metabolism was observed in Lactobacillus bulgaricus during adaptation to pH 4.9 (Fernandez et al, 2008). Fernandez et al suggested that pyruvate was rerouted to favor FA biosynthesis in order to change membrane fluidity in respond to acid stress (Fernandez et al, 2008). In agreement with this hypothesis, transcriptome results showed that FA biosynthesis was up-regulated in L. rhamnosus GG at pH 4.8 .…”

“…Similar results had been previously described in Lactobacillus rhamnosus GG where Ldh was found to be less abundant and pyruvate dehydrogenase complex E2 component (PdhC) more abundant when grown at pH 4.8 relative to pH 5.8, suggesting a shift of pyruvate metabolism towards the formation of acetyl-CoA . Furthermore, the same change in pyruvate metabolism was observed in Lactobacillus bulgaricus during adaptation to pH 4.9 (Fernández et al, 2008).…”

“…In Lactobacillus rhamnosus GG lactate dehydrogenase (Ldh) was found to be less abundant and pyruvate dehydrogenase complex E2 component (PdhC) more abundant when grown at pH 4.8 relative to pH 5.8, suggesting a shift of pyruvate metabolism to the formation of acetil-CoA and not to lactate . The same change in pyruvate metabolism was observed in Lactobacillus bulgaricus during adaptation to pH 4.9 (Fernandez et al, 2008). Fernandez et al suggested that pyruvate was rerouted to favor FA biosynthesis in order to change membrane fluidity in respond to acid stress (Fernandez et al, 2008).…”

“…Similarly several chaperonins involved in protein turnover are also essential to counteract protein damage upon acid exposure ( Figure 6, step 3). Studies of acid adaptation in Lactobacillus bulgaricus showed induction of the chaperones GroES, GroEL, HrcA, GrpE, DnaK, DnaJ, ClpE, ClpP, and ClpL, and the repression of ClpC (Fernandez et al, 2008).…”

“…The ability of probiotic microorganisms to survive to their transit through the gastrointestinal tract (tolerance to gastric and bile acid, and resistance to digestive enzymes) as well as industrial processing of food and storage, in order to arrive to their place of action in sufficient amounts, in a viable and active state, is of major importance and one of the selection criteria for probiotic strains (Food and Agriculture Organization of the United Nations & World Health Organization, 2006). Due to the interest of lactobacilli as probiotic and industrial bacteria, numerous studies address their efforts to determine the mechanisms of stress response enhancing their survival against the environmental challenges they are exposed to Murga et al, 2000;Tymczyszyn et al, 2007;Fernandez et al, 2008;RivasSendra et al, 2011;.…”