Suppression of lactate production of Lactobacillus reuteri JCM1112 by co-feeding glycerol with glucose

Analysis of the effects of specific growth rate of Lactococcus lactis MG1363 on aerobic metabolism and its application to high-density culture

Lactic acid bacteria (LAB) are known to produce a large amount of lactate when cultured under non-aerated conditions, which inhibits their growth at high concentrations. Our previous studies have shown that LAB can be cultured without lactate production under aerated conditions at a low specific growth rate. In this study, we investigated the effects of specific growth rate on cell yield and the specific production rates of metabolites in aerated fed-batch cultures of Lactococcus lactis MG1363. The results showed that lactate and acetoin production could be suppressed at specific growth rates below 0.2 h^-1, whereas acetate production was the highest at a specific growth rate of 0.2 h^-1. When LAB was cultured at a specific growth rate of 0.25 h^-1 with the addition of 5 mg/L heme to assist ATP production by respiration, lactate and acetate production was suppressed, and cell concentration reached 19 g-dry-cell/L (5.6 × 10ˆ10 cfu/mL) with a high cell yield of 0.42 ± 0.02 g-dry-cell/g-glucose.

Physiological significance of elevated levels of lactate by exercise training in the brain and body

For the past 200 years, lactate has been regarded as a metabolic waste end product that causes fatigue during exercise. However, lactate production is closely correlated with energy metabolism. The lactate dehydrogenase-catalyzed reaction uses protons to produce lactate, which delays ongoing metabolic acidosis. Of note, lactate production differs depending on exercise intensity and is not limited to muscles. Importantly, controlling physiological effect of lactate may be a solution to alleviating some chronic diseases. Released through exercise, lactate is an important biomarker for fat oxidation in skeletal muscles. During recovery after sustained strenuous exercise, most of the lactate accumulated during exercise is removed by direct oxidation. However, as the muscle respiration rate decreases, lactate becomes a desirable substrate for hepatic glucose synthesis. Furthermore, improvement in brain function by lactate, particularly, through the expression of vascular endothelial growth factor and brain-derived neurotrophic factor, is being increasingly studied. In addition, it is possible to improve stress-related symptoms, such as depression, by regulating the function of hippocampal mitochondria, and with an increasingly aging society, lactate is being investigated as a preventive agent for brain diseases such as Alzheimer's disease. Therefore, the perception that lactate is equivalent to fatigue should no longer exist. This review focuses on the new perception of lactate and how lactate acts extensively in the skeletal muscles, heart, brain, kidney, and liver. Additionally, lactate is now used to confirm exercise performance and should be further studied to assess its impact on exercise training.

Development of probiotics beverage using cereal enzymatic hydrolysate fermented with Limosilactobacillus reuteri

Although most probiotic products are milk based, lactose intolerance and vegetarianism inspired the idea of developing nondairy probiotic products. In this study, probiotic beverages were produced from four enzymatically hydrolyzed cereal substrates (coix seed, quinoa, millet, and brown rice) and fermented by Limosilactobacillus reuteri. Fermentation parameters, including pH, titratable acidity, viable count, organic acids, and volatile components were determined. Results showed that the pH values decreased and titratable acidity increased with the fermentation process (p < .05). Although the final pH in all samples was below 4.0, the growth of L. reuteri was not significantly inhibited by low pH. The number of viable bacteria (12.96 log CFU/ml) in coix seed substrate was significantly higher than that in other samples after the fermentation for 24 h (p < .05). Lactic acid and acetic acid were the main organic acids after fermentation and the highest in quinoa (lactic acid: 7.58 mg/ml; acetic acid: 2.23 mg/ml). The flavor analysis indicated that there were differences in the flavor components of different cereal beverages. Forty-nine volatile compounds were identified in four beverages, including acids, alcohols, aldehydes, ketones, and esters. The results of the electronic tongue showed that the umami taste of the fermented coix seed was better than that of other samples, displaying the more pleasant taste characteristics. In conclusion, it is feasible to prepare probiotic symbiotic cereal beverage with L. reuteri as starter culture. This study provides a reference for the development of nondairy probiotic products.

Culture conditions affect Lactobacillus reuteri DSM 17938 ability to perform glycerol bioconversion into 3-hydroxypropionic acid

The platform molecule 3-hydroxypropionic acid (3-HP) can be produced using Lactobacillus reuteri through a two-step bioprocess that involves a growth phase followed by a bioconversion phase. The bioproduction is performed by resting cells that convert glycerol into 3-HP and 1,3-propanediol in fed-batch mode. This work aimed at studying the effect of the growth conditions of L. reuteri DSM 17938 during the first step, on the glycerol bioconversion into 3-HP during the second step. A Plackett and Burman design was carried out to test, in controlled bioreactors, the effect of 11 growth conditions simultaneously, at fixed bioconversion conditions. The supplementation of the growth medium with vitamin B12 and cysteine displayed a negative effect on the 3-HP bioproduction. The addition of glucose, phytone peptone, Tween 80, 1,2-propanediol and betaine in the growth medium, together with a low temperature and an optimal pH of 6.0 during the growth phase increased the bioconversion duration from 56 h to 89 h at a glycerol feeding rate of 0.5 g·h^-1. A validating experiment displayed that the 3-HP titer, 3-HP production yield and 3-HP specific production rate were significantly improved by 25 %, 150 % and 61 %, respectively.

Suppression of lactate production by aerobic fed-batch cultures of Lactococcus lactis

Aerobic fed-batch cultures were studied as a means of suppressing the production of lactate, which inhibits the growth of lactic acid bacteria (LAB). LAB produce lactate via lactate dehydrogenase (LDH), regenerating nicotinamide adenine dinucleotide (NAD⁺) consumed during glycolysis. Therefore, we focused on NADH oxidase (NOX), employing oxygen as an electron acceptor, as an alternative pathway to LDH for NAD⁺ regeneration. To avoid glucose repression of NOX and NAD⁺ consumption by glycolysis exceeding NAD⁺ regeneration by NOX, glucose was fed gradually. When Lactococcus lactis MG 1363 was aerobically fed at a specific growth rate of 0.2 h^-1, the amount of lactate produced per amount of grown cell was reduced to 12% of that in anaerobic batch cultures. Metabolic flux analysis revealed that in addition to NAD⁺ regeneration by NOX, ATP acquisition by production of acetate and NAD⁺ regeneration by production of acetoin and 2,3-butanediol contributed to suppression of lactate production.

Suppression of lactate production in fed-batch culture of some lactic acid bacteria with sucrose as the carbon source

We report a method for suppression of lactate production by lactic acid bacteria (LAB) in culture. LAB produce lactate to regenerate NAD⁺ that is consumed during glycolysis. Glucose suppresses NAD⁺ regeneration pathways other than lactate dehydrogenase and non-glycolytic ATP production pathways. Therefore, the carbon source was changed to sucrose, and fed-batch culture was performed to limit the glycolytic flux and thus suppress lactate production. As a result, lactate productivity (i.e., the amount of lactate produced per amount of grown cell) in the sucrose/fed-batch culture was decreased compared to that in glucose/batch culture, in all five LAB strains examined. The productivity level decreased to 24% and 46% in Lactobacillus reuteri JCM 1112 and Lactococcus lactis JCM 7638, respectively. Metabolic flux analysis of Lactobacillus reuteri JCM 1112 revealed increased contributions of the mannitol production pathway to NAD⁺ regeneration and the arginine deiminase pathway to ATP production in the sucrose/fed-batch culture.