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The aim of this work was to investigate the effect of pulsed electric fields (PEF) on the growth and acidification kinetics of Lactobacillus delbrueckii subsp. bulgaricus CFL1 during fermentation. The PEF treatments were applied during the fermentation process using a recirculation pump and a PEF treatment chamber coupled with a PEF generator. The medium flow rate through the chamber was first optimized to obtain the same growth and acidification kinetics than the control fermentation without medium recirculation. Different PEF intensities (60–428 V cm−1) were then applied to the culture medium to study the impact of PEF on the cells’ behavior. The growth and acidification kinetics were recorded during the fermentation and the specific growth rates µ, pH, and acidification rate (dpH/dt) were assessed. The results obtained showed a biphasic growth by applying high PEF intensities (beyond 285 V cm−1) with the presence of two maximal specific growth rates and a decrease in the acidification activities. It was demonstrated that the cells were stressed during the PEF treatment, but presented an accelerated growth after stopping it, leading thereby to similar absorbance and pH at the end of the fermentation. These results show the great potential of PEF technology to be applied to generate low acidified products by performing PEF-assisted fermentations.

Background CodY (Control of dppY) is a global transcriptional regulator of Streptococcus thermophilus (ST). In this study, we utilized a S. thermophilus codY gene deletion mutant strain to explore metabolites that may affect the oxidative-stress resistance of Lactobacillus delbrueckii subsp. bulgaricus . The context of this research is to understand the role of CodY in the interaction between S. thermophilus and L. delbrueckii , particularly focusing on the impact of CodY on the oxidative-stress resistance of L. delbrueckii . Results Firstly, the ST-1Δ codY mutant strain was constructed by the knockout technique. We found that codY gene deletion significantly reduced the growth rate and resistance to oxidative stress of L. delbrueckii in co-culture, with a decrease in viable bacterial count to 5.26 ± 0.04 log(cfu/mL), and a decrease in survival by 15% and 25% under 5 mM and 10 mM H 2 O 2 stress, respectively. Metabolites were comprehensively analyzed under three different culture conditions, and we identified 35 differentiated metabolites associated with CodY regulation. These metabolites were screened by their significant differential metabolite expression folds (up- or down-regulation) under different culture conditions, and Variable Importance in Projection (VIP) values assessed their significance, fold changes, and P values. Further, we identified six compounds, including lysine, 4-hydroxyphenylacetic acid, cycloleucine, glycine-L-lysine, 3-hydroxyphenylacetic acid, and N 6 -acetyl-L-lysine, which significantly enhanced the oxidative-stress resistance of L. delbrueckii . The viable counts of L. delbrueckii were increased by 7.73%, 6.49%, 4.27%, 3.62%, 2.12%, and 1.38%, respectively, in the medium supplemented with these substances under the stress of 10 mM H 2 O 2 . Conclusions The study results are important for understanding the synergistic effect of the two bacteria during fermentation and their response to environmental stresses. The findings provide insights into the role of CodY in modulating the oxidative-stress resistance of L. delbrueckii and highlight the potential of identified metabolites to enhance the performance of this bacterium under stress conditions. This could have implications for the development of strategies to improve the robustness of industrial fermentation processes involving these bacteria.

Lactobacillus delbrueckii ssp. bulgaricus (L. bulgaricus) is a representative of the group of lactic acid-producing bacteria, mainly known for its worldwide application in yogurt production. The genome sequence of this bacterium has been determined and shows the signs of ongoing specialization, with a substantial number of pseudogenes and incomplete metabolic pathways and relatively few regulatory functions. Several unique features of the L. bulgaricus genome support the hypothesis that the genome is in a phase of rapid evolution. (i) Exceptionally high numbers of rRNA and tRNA genes with regard to genome size may indicate that the L. bulgaricus genome has known a recent phase of important size reduction, in agreement with the observed high frequency of gene inactivation and elimination; (ii) a much higher GC content at codon position 3 than expected on the basis of the overall GC content suggests that the composition of the genome is evolving toward a higher GC content; and (iii) the presence of a 47.5-kbp inverted repeat in the replication termination region, an extremely rare feature in bacterial genomes, may be interpreted as a transient stage in genome evolution. The results indicate the adaptation of L. bulgaricus from a plant-associated habitat to the stable protein and lactose-rich milk environment through the loss of superfluous functions and protocooperation with Streptococcus thermophilus.

Immune senescence potentially leads to an increased risk of infections. It is desirable to augment the immune system and protect against infections by daily consumption of immunostimulatory food. The present study evaluated whether the intake of yoghurt fermented with Lactobacillus delbrueckii ssp. bulgaricus (L. bulgaricus) OLL1073R-1 has an effect on resistance to the common cold. We conducted two independent studies, in which fifty-seven (median age 74·5 years) and eighty-five healthy elderly individuals (median age 67·7 years) were participants. In each study, the subjects were divided into two groups based on age and sex and instructed to eat 90 g yoghurt or drink 100 ml milk once per d over an 8- or 12-week period. A meta-analysis of the results of these two independent studies showed the risk of catching the common cold was about 2·6 times lower (OR 0·39; P = 0·019) in the yoghurt group than in the milk group and the increase of natural killer cell activity was significantly higher in the yoghurt group than in the milk group (P = 0·028). In addition, the quality of life score for the ‘eye/nose/throat’ system after intake was significantly higher in the yoghurt group than in the milk group and the improvement of the score was correlated with the promotion of natural killer cell activity. In conclusion, consumption of yoghurt fermented with L. bulgaricus OLL1073R-1 augmented natural killer cell activity and reduced the risk of catching the common cold in elderly individuals.

The probiotic efficacy and fermentative ability of Lactobacillus delbrueckii subsp. bulgaricus (L. bulgaricus), a widely used probiotic, is majorly affected by its acid tolerance. Here, we conducted whole-genome sequencing of the high acid-tolerant L. bulgaricus LJJ stored in the laboratory. Compared with the whole genome of low acid-tolerant strain L. bulgaricus ATCC11842, the results show that 16 candidate acid-tolerant genes may be involved in the regulation of the acid tolerance of L. bulgaricus LJJ. Association analysis of candidate acid-tolerant genes and acid-tolerant traits of different L. bulgaricus strains revealed that the three genes dapA, dapH, and lysC are the main reasons for the strong acid tolerance of L. bulgaricus LJJ. The results of real-time quantitative PCR (RT-qPCR) supported this conclusion. KEGG pathway analysis showed that these three acid-tolerant genes are involved in the synthesis of lysine; the synthesis of lysine may confer L. bulgaricus LJJ strong acid tolerance. This study successfully revealed the acid tolerance mechanism of L. bulgaricus LJJ and provides a theoretical basis for the subsequent selection of strains with high acid tolerance for improved probiotic functions.Key points• Three genes are identified as acid-tolerant genes, respectively, lysC, dapA, and dapH.• LysC and dapA are the major key genes in the synthesis of lysine.• The synthesis of lysine may confer L. bulgaricus LJJ strong acid tolerance.

Folate deficiency is a public health concern affecting all age groups worldwide. The available evidence reveals that adding probiotic bacteria to the yoghurt starter cultures during yoghurt production process under fermentation conditions increases the folate content of yoghurt. The present study was conducted to measure two folate derivatives, i.e., 5-methyltetrahydrofolate and 5-formyltetrahydrofolate, in bio-fortified yoghurt samples including (1) yoghurt containing Streptococcus thermophilus and Lactobacillus bulgaricus , (2) probiotic yoghurt containing Lactobacillus acidophilus LA-5 and Bifidobacterium lactis BB-12, (3) probiotic yoghurt containing native strains of Lactobacillus plantarum 15HN, (4) probiotic yoghurt containing native strains of Lactococcus lactis 44Lac, and (5) probiotic yoghurt containing commercial strains of Lactobacillus plantarum LAT BY PL. During storage at 4 °C for 21 days, the highest levels of 5-methyltetrahydrofolate and 5-formyltetrahydrofolate, which were statistically significant, were detected in the yoghurt made using Lact . plantarum 15HN. Moreover, the highest total folate concentration (1487 ± 96.42 μg/L) was specified in the yoghurt containing Lact . plantarum 15HN on the 7th day. It can be conjectured that this product can be suggested as a proper alternative to synthetic folic acid and may not have the side effects of using synthetic folic acid overdoses.

ObjectiveIts eps gene cluster, the antioxidant activity and monosaccharide composition of exopolysaccharides, the expression levels of related genes at different fermentations were analyzed for clarifying the exopolysaccharide biosynthesis mechanism of Lactobacillus delbrueckii subsp. bulgaricus LDB-C1.ResultsThe comparison analysis of eps gene clusters indicated that the gene clusters present diversity and strain specificity. The crude exopolysaccharides from LDB-C1 exhibited a good antioxidant activity. Compared with glucose, fructose, galactose, and fructooligosaccharide, inulin significantly improved the exopolysaccharide biosynthesis. The structures of EPSs were significantly different under different carbohydrate fermentation conditions. Inulin obviously increased the expressions of most EPS biosynthesis related genes at fermentation 4 h.ConclusionInulin accelerated the beginning of the exopolysaccharide production in LDB-C1, and the enzymes promoted by inulin was beneficial for the accumulation of exopolysaccharide at the whole fermentation process.

Lead (Pb) is a toxic contaminating heavy metal that can cause a variety of hazardous effects to both humans and animals. In the present study, Lactobacillus delbrueckii subsp. bulgaricus KLDS1.0207 (L. bulgaricus KLDS1.0207), which has a remarkable Pb binding capacity and Pb tolerance, was selected for further study. It was observed that the thermodynamic and kinetic model of L. bulgaricus KLDS1.0207 Pb binding respectively fit with the Langmuir–Freundlich model and the pseudo second-order kinetic model. Scanning electron microscopy and energy dispersive spectroscopy analysis disclosed that the cell surfaces were covered with Pb and that carbon and oxygen elements were chiefly involved in Pb binding. Combined with Fourier transform infrared spectroscopy analysis, it was revealed that the carboxyl, phosphoryl, hydroxyl, amino and amide groups were the main functional groups involved in the Pb adsorption. The protective effects of L. bulgaricus KLDS1.0207 against acute Pb toxicity in mice was evaluated by prevention and therapy groups, the results in vivo showed that L. bulgaricus KLDS1.0207 treatment could reduce mortality rates, effectively increase Pb levels in the feces, alleviate tissue Pb enrichment, improve the antioxidant index in the liver and kidney, and relieve renal pathological damage. Our findings show that L. bulgaricus KLDS1.0207 can be used as a potential probiotic against acute Pb toxicity.

It is a practice to add microalgae into plain and probiotic fermented milks in order to promote the functionality of these products via their direct health effects as well as the enhancing impact on viability of probiotic microorganisms in product and in gastrointestinal tract. In this study, the effects of addition of two species of microalgae including Arthrospira platensis and Chlorella vulgaris (seven yogurt treatments containing three concentrations for each microalgae—0.25, 0.50, and 1.00 %—and a control without microalgae) on pH, titrable acidity, and redox potential changes as well as on the viability of probiotic bacteria during fermentation and during a 28-day refrigerated storage period (5 °C) were investigated in yogurt. Also, the amounts of lactic and acetic acids at the end of fermentation were assessed. The culture composition of yogurt was ABY type, containing Lactobacillus acidophilus LA-5, Bifidobacterium lactis BB-12, Lactobacillus delbrueckii ssp. bulgaricus, and Stresptococcus themophilus . The addition of microalgae significantly ( p  < 0.05) increased the viability of L. acidophilus and bifdobacteria at the end of fermentation and during the storage period. Treatments containing A. platensis had slower pH decline, faster acidity increase, longer incubation time, and greater final titrable acidity than those containing C. vulgaris and control. In treatments containing 0.5 or 1 % microalgae, the viability was almost higher than 10 7 cfu/mL until the end of refrigerated storage.

Lactobacillus delbrueckii subsp. bulgaricus (L. bulgaricus) is a microaerophylic anaerobe, which is widely used in the production of yogurt, cheese, and other fermented dairy products. L. bulgaricus and its partner Streptococcus thermophilus were used as starter cultures of yogurt in the world for thousands of years. In our previous study, L. bulgaricus LDB-C1 was obtained from traditional fermented milk, and possessed some characteristics like high exopolysaccharide yield and good fermentation performance. The analysis of its CRISPR–Cas system, antibiotic resistance, virulence factors, and mobile elements, was performed to reveal the stability of the strain LDB-C1. It was found that LDB-C1 contains a plenty of spacers in the CRISPR region, indicating it might have better performance against the infection of phages and plasmids. Furthermore, the acquired or transmittable antibiotic resistance/virulence factor genes were absent in the tested L. bulgaricus strain LDB-C1.