Project description:We investigated the effects of jeotgal (fermented fish sauce) on kimchi fermentation, with or without saeu-jeot and myeolchi-jeot. Bacterial community analysis showed that Leuconostoc, Weissella, Lactobacillus, and Tetragenococcus were the dominant genera; however, their succession depended on the presence of jeotgal. Leuconostoc gasicomitatum was the dominant species in kimchi without jeotgal, whereas Weissella koreensis and Lactobacillus sakei were the dominant species in kimchi with myeolchi-jeot and saeu-jeot, respectively. Metabolite analysis, using 1H NMR, showed that the amounts of amino acids and gamma-aminobutyric acid (GABA) were higher in kimchi with jeotgal. Increases in acetate, lactate, and mannitol contents depended on fructose consumption and were more rapid in kimchi with jeotgal. Moreover, the consumption of various amino acids affected the increase in kimchi LAB. Thus, the role of jeotgal in kimchi fermentation was related to enhancement of taste, the amino acid source, and the increases in levels of functional metabolites.
Project description:Purpose: High γ-aminobutyric acid (GABA)-producing Levilactobacillus brevis strain NPS-QW 145 along with Streptococcus thermophilus (one of the two starter bacteria used to make yogurt for its proteolytic activity) to enhance GABA production in milk. But a mechanistic understanding on how Levilactobacillus brevis cooperated with S. thermophilus to stimulate GABA production has been lacking. Method: Metatranscriptomic analyses combined with peptidomics were carried out to unravel the casein and lactose utilization patterns during milk fermentation with the co-culture. Results: We found particular peptides hydrolyzed by S. thermophilus 1275 were transported and biodegraded with peptidase in Lb. brevis 145 to meet the growth needs of the latter. In addition, amino acid synthesis and metabolism in Lb. brevis 145 were also activated to further support its growth. Glucose, as a result of lactose hydrolysis by S. thermophilus 1275, but not available lactose in milk, was outcompeted by Lb. brevis 145 as a main carbon source for glycolysis to produce ATP.In the stationary phase, under the acidic condition due to accumulation of lactic acid produced by S. thermophilus 1275, genes expression involved in pyridoxal phosphate (coenzyme of glutamic acid decarboxylase) metabolism and glutamic acid decarboxylase (Gad) in Lb. brevis 145 were induced for GABA production.
Project description:Lactococcus lactis is the main bacterium used for food fermentation and is a candidate for probiotic development. In addition to fermentation growth, supplementation with heme in aerobic conditions activates a cytochrome oxidase, which promotes respiration metabolism. In contrast to fermentation in which cells consume energy to produce mainly lactic acid, respiration metabolism dramatically changes energy metabolism, such that massive amounts of acetic acid and acetoin are produced at the expense of lactic acid. Our goal was to investigate the metabolic changes that correlate with significantly improved growth and survival during respiration growth. Using transcriptional time course analyses, mutational analyses, and promoter reporter fusions, we uncover two main pathways that can explain the robust growth and stability of respiration cultures: The acetate pathway contributes to biomass yield in respiration, without affecting medium pH. The acetoin pathway allows cells to cope with internal acidification, which directly affects cell density and survival in stationary phase. Our results suggest that manipulation of these pathways could lead to fine tuning respiration growth, with improved yield and stability.
Project description:The present study aims to explore chemostat-based transcriptome analysis of mixed cultures by investigating interactions between the yeast S. cerevisiae and the lactic acid bacterium L. bulgaricus . S. cerevisiae and L. bulgaricus are both frequently encountered in kefir, a fermented dairy product. In the context of this study, this binary culture serves as a model for the many traditional food and beverage fermentation processes in which yeasts and lactic acid bacteria occur together. The design of the cultivation conditions was based on the observation that L. bulgaricus, but not S. cerevisiae, can use lactose as a carbon source for growth and that S. cerevisiae, but not L. bulgaricus, can grow on galactose that is released upon hydrolysis of lactose by the bacterial β-galactosidase. Mixed populations of yeasts and lactic acid bacteria occur in many dairy, food and beverage fermentations, but knowledge about their interactions is incomplete. In the present study, interactions between Saccharomyces cerevisiae and Lactobacillus delbrueckii subsp. bulgaricus, two microorganisms that co-occur in kefir fermentations, were studied during anaerobic growth on lactose. By combining physiological and transcriptome analysis of the two strains in the co-cultures, five mechanisms of interaction were identified. 1. L. bulgaricus hydrolyses lactose, which cannot be metabolized by S. cerevisiae, to galactose and glucose. Subsequently, galactose, which cannot be metabolized by L. bulgaricus, is excreted and provides a carbon source for yeast. 2. In pure cultures, L. bulgaricus only grows at increased CO2 concentrations. In anaerobic mixed cultures, the yeast provides this CO2 via alcoholic fermentation. 3. Analysis of amino acid consumption from the defined medium indicated that S. cerevisiae supplied alanine to the bacteria. 4. A mild but significant low-iron response in the yeast transcriptome, identified by DNA microarray analysis, was consistent with the chelation of iron by the lactate produced by L. bulgaricus. 5. Transcriptome analysis of L. bulgaricus in mixed cultures showed an overrepresentation of transcripts involved in lipids metabolism suggesting either a competition of the two microorganisms for fatty acids, or a response to the ethanol produced by S. cerevisiae.