Streptococcus thermophilus is one of the most widely used lactic acid bacteria in the dairy industry, in particular in yoghurt manufacture, where it is associated with Lactobacillus delbrueckii subsp. bulgaricus. This bacterial association, known as a proto-cooperation, is poorly documented at the molecular and regulatory levels. We thus investigate the kinetics of the transcriptomic and proteomic modifications of S. thermophilus LMG 18311 in response to the presence of L. delbrueckii subsp. bulgaricus ATCC 11842 during growth in milk at two growth stages. Seventy-seven different genes or proteins (4.1% of total coding sequences), implicated mainly in the metabolism of nitrogen (24%), nucleotide base (21%), and iron (20%), varied specifically in coculture. One of the most unpredicted results was a significant decrease of most of the transcripts and enzymes involved in purine biosynthesis. Interestingly, the expression of nearly all genes potentially encoding iron transporters of S. thermophilus decreased, whereas that of iron-chelating dpr as well as that of the fur (perR) regulator genes increased, suggesting a reduction in the intracellular iron concentration, probably in response to H 2 O 2 production by L. bulgaricus. The present study reveals undocumented nutritional exchanges and regulatory relationships between the two yoghurt bacteria, which provide new molecular clues for the understanding of their associative behavior.

Background: Management of blood cholesterol is a major focus of efforts to prevent cardiovascular diseases. The objective of this study was to investigate how the gut microbiota affects host cholesterol homeostasis at the organism scale. Results: We depleted the intestinal microbiota of hypercholesterolemic female Apoe −/− mice using broad-spectrum antibiotics. Measurement of plasma cholesterol levels as well as cholesterol synthesis and fluxes by complementary approaches showed that the intestinal microbiota strongly regulates plasma cholesterol level, hepatic cholesterol synthesis, and enterohepatic circulation. Moreover, transplant of the microbiota from humans harboring elevated plasma cholesterol levels to recipient mice induced a phenotype of high plasma cholesterol levels in association with a low hepatic cholesterol synthesis and high intestinal absorption pattern. Recipient mice phenotypes correlated with several specific bacterial phylotypes affiliated to Betaproteobacteria, Alistipes, Bacteroides, and Barnesiella taxa. Conclusions: These results indicate that the intestinal microbiota determines the circulating cholesterol level and may thus represent a novel therapeutic target in the management of dyslipidemia and cardiovascular diseases.

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.

No abstract

BackgroundLactobacillus delbrueckii ssp. lactis and ssp. bulgaricus are lactic acid producing bacteria that are largely used in dairy industries, notably in cheese-making and yogurt production. An earlier in-depth study of the first completely sequenced ssp. bulgaricus genome revealed the characteristics of a genome in an active phase of rapid evolution, in what appears to be an adaptation to the milk environment. Here we examine for the first time if the same conclusions apply to the ssp. lactis, and discuss intra- and inter-subspecies genomic diversity in the context of evolutionary adaptation.ResultsBoth L. delbrueckii ssp. show the signs of reductive evolution through the elimination of superfluous genes, thereby limiting their carbohydrate metabolic capacities and amino acid biosynthesis potential. In the ssp. lactis this reductive evolution has gone less far than in the ssp. bulgaricus. Consequently, the ssp. lactis retained more extended carbohydrate metabolizing capabilities than the ssp. bulgaricus but, due to high intra-subspecies diversity, very few carbohydrate substrates, if any, allow a reliable distinction of the two ssp. We further show that one of the most important traits, lactose fermentation, of one of the economically most important dairy bacteria, L. delbruecki ssp. bulgaricus, relies on horizontally acquired rather than deep ancestral genes. In this sense this bacterium may thus be regarded as a natural GMO avant la lettre.ConclusionsThe dairy lactic acid producing bacteria L. delbrueckii ssp. lactis and ssp. bulgaricus appear to represent different points on the same evolutionary track of adaptation to the milk environment through the loss of superfluous functions and the acquisition of functions that allow an optimized utilization of milk resources, where the ssp. bulgaricus has progressed further away from the common ancestor.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2164-15-407) contains supplementary material, which is available to authorized users.

Alterations in the gut microbiota composition and diversity seem to play a role in the development of chronic diseases, including inflammatory bowel disease (IBD), leading to gut barrier disruption and induction of proinflammatory immune responses. This opens the door for the use of novel health-promoting bacteria. We selected five Parabacteroides distasonis strains isolated from human adult and neonates gut microbiota. We evaluated in vitro their immunomodulation capacities and their ability to reinforce the gut barrier and characterized in vivo their protective effects in an acute murine model of colitis. The in vitro beneficial activities were highly strain dependent: two strains exhibited a potent anti-inflammatory potential and restored the gut barrier while a third strain reinstated the epithelial barrier. While their survival to in vitro gastric conditions was variable, the levels of P. distasonis DNA were higher in the stools of bacteria-treated animals. The strains that were positively scored in vitro displayed a strong ability to rescue mice from colitis. We further showed that two strains primed dendritic cells to induce regulatory T lymphocytes from naïve CD4+ T cells. This study provides better insights on the functionality of commensal bacteria and crucial clues to design live biotherapeutics able to target inflammatory chronic diseases such as IBD.

Streptococcus thermophilus is a thermophilic lactic acid bacterium widely used as starter in the manufacture of dairy products in particular in yoghurt manufacture in combination with Lactobacillus delbrueckii ssp. bulgaricus. However, in spite of its massive use, the physiological state of S. thermophilus in milk has hardly been investigated. We established the first map of the cytosolic proteome of S. thermophilus LMG18311 grown in milk. It comprises 203 identified proteins corresponding to 32% of theoretical proteome. In addition, using proteomic and transcriptomic approaches, we analyzed the physiology of LMG18311 during its late stage of growth in milk (between 2h30 and 5h30). It revealed the up-regulation of (i) peptides and AA transporters and of specific AA biosynthetic pathways notably for sulfur AA and (ii) genes and proteins involved in the metabolism of various sugars. These two effects were also observed in LMG18311 grown in milk in coculture with L. bulgaricus although the effect on sugar metabolism was less pronounced. It suggests that the stimulatory effect of Lactobacillus on the Streptococcus growth is more complex than AA or peptides supply.

The role of the gut microbiota in health and disease is well recognized and the microbiota dysbiosis observed in many chronic diseases became a new therapeutic target. The challenge is to get a better insight into the functionality of commensal bacteria and to use this knowledge to select live biotherapeutics as new preventive or therapeutic products. In this study, we set up a screening approach to evaluate the functional capacities of a set of 21 strains isolated from the gut microbiota of neonates and adults. For this purpose, we selected key biological processes involved in the microbiome-host symbiosis and known to impact the host physiology i.e., the production of short-chain fatty acids and the ability to strengthen an epithelial barrier (Caco-2), to induce the release of the anti-inflammatory IL-10 cytokine after co-culture with human immune cells (PBMC) or to increase GLP-1 production from STC-1 endocrine cell line. This strategy highlighted fifteen strains exhibiting beneficial activities among which seven strains combined several of them. Interestingly, this work revealed for the first time a high prevalence of potential health-promoting functions among intestinal commensal strains and identified several appealing novel candidates for the management of chronic diseases, notably obesity and inflammatory bowel diseases.