Increase In Lactic Acid Production Research Articles

Dynamic Optimization of Lactic Acid Production from Grape Stalk Solid-State Fermentation with Rhizopus oryzae Applying a Variable Temperature Profile

Lactic acid is widely used in the food industry. It can be produced via chemical synthesis or biotechnological pathways by using renewable resources as substrates. The main challenge of sustainable production lies in reaching productivities and yields that allow for their industrial production. In this case, the application of process engineering becomes a crucial tool to improve the performance of bioprocesses. In this work, we performed the solid-state fermentation of grape stalk using Rhizopus oryzae NCIM 1299 to obtain lactic acid, employing three different temperatures (22, 35, and 40 °C) and a relative humidity of 50%. The Logistic and First-Order Plus Dead Time models were adjusted for fungal biomass growth, and the Luedeking and Piret with Delay Time model was used for lactic acid production, obtaining higher R2 values in all cases. At 40 °C, it was observed that Rhizopus oryzae grew in pellet form, resulting in an increase in lactic acid productivity. In this context, the effect of temperature on the kinetic parameters was evaluated with a polynomial correlation. Finally, using this correlation, a smooth and continuous optimal temperature profile was obtained by a dynamic optimization method, improving the final lactic acid concentration by 53%.

Characterization of physicochemical and microbial quality, functional properties, and shelf stability of fermented tigernut-based probiotic beverages

Tigernuts and millet are indigenous underutilized crops in West Africa that have versatile applications in food processing. These crops are rich in fermentable carbohydrates, resistant starch, fiber, and micronutrients, making them ideal candidates for pre- and probiotic (synbiotic) foods. This study utilized whole tigernuts in a dairy–millet-based fermented beverage called brukina, turned it to a synbiotic, and assessed the functional and physicochemical profiles, microbial quality, and shelf stability of the beverage. The tigernut–millet agglomerate was prepared by incorporating cellulose-hydrolyzed tigernut fibrous (TNF) cake and non-hydrolyzed TNF (10% and 15%, respectively) into millet and allowing to ferment for 12 and 24 h. Brukina produced from composite tigernut milk: dairy in a ratio of 40%:60% was inoculated with the probiotic Lacticaseibacillus casei after pasteurization. The beverage was analyzed for physicochemical, proximate, and functional properties and microbiological stability at 5°C and 25°C. The obtained data were subjected to analysis of variance (ANOVA) in Minitab version 17 using a general linear model to determine the variability, interactions, and significance of the measured product characteristics. The agglomerate water absorption capacity (l/g) ranged from 0.70 ± 0.17 to 0.89 ± 0.17, bulk density (g/l) from 0.55 ± 0.04 to 0.63 ± 0.00, and swell index (%) from 1.62 ± 0.08 to 1.80 ± 0.06. The agglomerate prepared from dough and fermented for 12 h had excellent functional characteristics and was selected for synbiotic brukina production. Moisture content of the product decreased (p < 0.001) with tigernut incorporation ranging from 78.85% to 70.45%, while sodium, phosphorus, protein, total carbohydrate, and crude fiber increased with tigernut incorporation (p < 0.05). Synbiotic brukina supported the growth of L. casei attaining 11 log CFU/mL with a corresponding increase in lactic acid production and was microbiologically safe at 5°C and 25°C for 5 days compared to unpasteurized and uninoculated probiotic control (p < 0.05). The addition of whole tigernuts and L. casei to brukina enhanced its nutritional content with a shelf stability of 3 days.

Influence of secretome obtained from preovulatory follicular fluid on energy metabolism and meiotic competence of equine cumulus–oocyte complexes

Secretome is composed by proteins and microvesicles secreted by the granulosa cells that line the follicular wall. These bioactive compounds promote follicular growth and oocyte maturation, influencing oocyte metabolism. Hence, we hypothesized that addition of secretome from preovulatory follicular fluid (FF) to maturation medium may influence the meiotic competence and metabolism of cumulus-oocyte-complexes (COCs) obtained post mortem. FF was retrieved from preovulatory follicles (2 mares) after 32h of hCG administration. Three ml of FF from both mares were pooled, diluted 1:1 in PBS and centrifuged (4000g, 1h at 4°C) using a 10K Amicon® Ultra-15 Centrifugal Filter Unit and protein concentration was measured. A total of 186 COCs were retrieved from post mortem ovaries and were subjected to in vitro maturation (IVM) in TCM-199 medium, 10% of FBS and 5 mU/ml of FSH (Control; 59 oocytes) or with 20 µg/ml of secretome (Secretome20; 66 oocytes) or with 40 µg/ml of secretome (Secretome40; 61 oocytes) for 28 h in 5% CO2/95% air at 38.2°C. Oocytes were denuded, fixed in 4% formaldehyde and stained with Hoechst 33342 to assess chromatin conformation by fluorescence microscopy. Also, selected metabolites of the maturation medium prior to andafter IVM were assessed by magnetic proton nuclear resonance spectroscopy. After IVM, a trend towards glucose consumption and pyruvic acid production was observed compared to their controls prior IVM; a significant increase in lactic acid production in all treatments was observed (Table 1; p < 0.05). Our results show a tendency for quicker meiosis resumption in COCs incubated with Secretome40 (Table 2). In conclusion, secretome obtained from preovulatory follicular fluid added during IVM does not change COCs’ energy metabolism nor maturation rate of equine cumulus-oocyte complexes in our in vitro culture system. Funding: MCCIN/AEI (PID2020-112723RB-I00; RYC-2017-21545; RYC2020-028915-I), Junta de Extremadura-FEDER (IB20005).

Gallic acid markedly stimulates GLUT1-mediated glucose uptake by the AsPC-1 pancreatic cancer cell line.

Phenolic acids are recognized as chemopreventive and chemotherapeutic agents. Altered glucose and glutamine metabolism are recognized hallmarks of cancer cells. We aimed to test the influence of phenolic acids on glucose and glutamine cellular uptake by a breast (MCF-7) and a pancreatic (AsPC-1) cancer cell line. Several phenolic acids (caffeic, ferrulic, proctocatechuic, coumaric and gallic acid) affected 3H-glutamine and/or 3H-deoxy-d-glucose (3H-DG) uptake. Gallic acid (100µM) caused a 3-fold increase in 3H-DG uptake by AsPC-1 cells, associated with a 3.7-fold increase in lactic acid production. Gallic acid stimulated GLUT1-mediated 3H-DG uptake and increased the affinity of this transporter for 3H-DG. We further verified that gallic acid does not change GLUT1 transcription rates and cellular redox state and that its effect does not involve PI3K, mTOR and MAP kinases and is not associated with a proproliferative effect. Gallic acid also increased 3H-DG uptake by MCF-7 cells, although less potently. Further investigation is necessary to elucidate the cellular pathways involved in this effect of gallic acid.

The responses of organic acid production and microbial community to different carbon source additions during the anaerobic fermentation of Chinese cabbage waste

The effects of glucose, fructose, sucrose and molasses on organic acid levels, protein degradation, nutrient preservation and bacteriome were studied during the anaerobic fermentation of Chinese cabbage waste. The results showed that fructose and molasses additions caused a significant (p < 0.05) increase in lactic acid production (82.16–89.79 %), acetic acid production (175.41–196.93 %), ammonia nitrogen formation (15.93–37.43 %) and reduction of neutral detergent fiber level (8.17–15.87 %). However, few positive effects of glucose and sucrose additions were found on organic acid production. Furthermore, carbon source additions enriched (p < 0.05) the acid-producing bacteria, such as Lactobacillus paralimentarius and Lactobacillus heilongjiangensis, upregulated (p < 0.05) the pathways of carbohydrate and lipid metabolisms and reduced (p < 0.05) the abundances of Lactobacillus buchneri and Escherichia coli and bacteria that were mobile elements-contained and stress-tolerant. Collectively, fructose and molasses additions enhanced the recycling of Chinese cabbage waste by anaerobic fermentation, in which the desired products are organic acids.

Production and evaluation of probioticated mango juice using Pediococcus pentosaceus and Pediococcus acidilactici during storage at different temperature

The incorporation of probiotics into fruit juices for the production of functional and nutraceutical food is of necessity in order to control lifestyle-related diseases and increase the availability of foods to a large population of lactose intolerant patients and vegetarians. Hence, the microbial viability, antagonistic activity, physicochemical, proximate minerals and organoleptic characterization of stored probioticated mango juice using Pediococcus pentosaceus and Pediococcus acidilactici as starter and unprobioticated samples were investigated. The viability of the probiotic strains decreased (3.37–0.47 × 10 7 and 4.05–0.34 × 10 7 CFU/mL) during storage. During the early weeks of storage at 4 and 25 °C, the probioticated juice samples displayed antagonistic activities against some of the test pathogens, including Klebsilla pneumonia, Escherichia coli, Pseudomonas aeruginosa, and Bacillus cereus, with E. coli being the most active. There was an increase in lactic acid production (17.75–19.10 and 19.28–20.54 mg/L) and vitamin C content (41.35–48.77 and 44.59–48.59). A significant reduction in pH (4.72–3.10 and 4.52–2.27), colour (76.12–77.00 and 77.66–74.79) and total soluble solid (9.14–5.25 and 9.17–6.82 o Brix) were observed during storage. There was no significant difference in proximate composition of samples stored at 4°C but a reduction in crude protein, crude fiber and carbohydrate of the samples stored at 25 °C. A significant increase in Fe, Ca and Na with a reduction in Mg content was observed. Samples stores at 4 °C had better acceptability in terms of taste, aroma, colour, or appearance compared to those stored at 25 °C. Mango juice is suitable for the production of probiotic beverage with functional and nutraceutical benefits. • Mango juice was successfully probioticated using two lactic acid bacteria - Pediococcus pentosaceus and Pediococcus acidilactici • Probioticated mango juice were more viable compared to unprobioticated ones • There was an improvement in the microbial viability of the probioticated mango juice at 4 and 25 o C of storage • Probioticated mango juice showed antagonistic activities against some test pathogens at early weeks of storage • Samples stores at 4 °C had better acceptability compared to those stored at 25 °C.

Optimization of Lactic Acid Production from Pineapple By-Products and an Inexpensive Nitrogen Source Using Lactiplantibacillus plantarum strain 4O8.

Lactic acid (LA) is used in food, cosmetic, chemical, and pharmaceutical industries and has recently attracted much attention in the production of biodegradable polymers. The expensive substances including carbon and nitrogen sources involved in its fermentative synthesis and the increasing market demand of LA have prompted scientists to look for inexpensive raw materials from which it can be produced. This research was aimed at determining the optimum conditions of lactic acid (LA) production from pineapple by-products and an inexpensive nitrogen source using Lactiplantibacillus plantarum strain 4O8. After collection and preparation of the carbon source (pineapple by-products) and nitrogen sources (by-products from fish, chicken, and beer brewing industries), they were used for the formulation of 4 different media in terms of nitrogen sources. Then, the proximate compositions of promising nitrogen sources were determined. This was followed by the screening of factors (temperature, carbon source, nitrogen source, MgSO4, MnSO4, FeSO4, KH2PO4, and KHPO4) influencing the production of LA using the definitive plan. Lastly, the optimization process was done using the central composite design. The highest LA productions (14.64 ± 0.05 g/l and 13.4 ± 0.02 g/l) were obtained in production medium supplemented with chicken and fish by-products, respectively, making them the most promising sources of nitrogen. The proximate analysis of these nitrogen sources revealed that their protein contents were 83.00 ± 1.41% DM and 74.00 ± 1.41% DM for chicken by-products and fish by-products, respectively. Concerning the screening of factors, temperature, nitrogen source, and carbon source were the factors that showed a major impact on LA production in the production medium containing chicken by-products as nitrogen source. A pineapple by-product concentration of 141.75 g/l, a nitrogen source volume of 108.99 ml/l, and a temperature of 30.89°C were recorded as the optimum conditions for LA production. The optimization led to a 2.73-fold increase in LA production when compared with the production medium without nitrogen source. According to these results, chicken by-products are a promising and an inexpensive nitrogen source that can be an alternative to yeast extract in lactic acid production.

Efficient utilization of hydrolysates from steam-exploded gardening residues for lactic acid production by optimization of enzyme addition and pH control

The expansion of urban green areas has boosted the accumulation of gardening lignocellulosic residues that could be potentially used to produce platform chemicals like lactic acid. However, when using lignocelluloses, pretreatment step, such as steam explosion, is often needed to favour sugar release. Considering that the conversion of glucose from cellulose has been widely addressed, this work is focused on the valorisation of the steam-exploded gardening liquid fraction rich in hemicellulosic sugars. Since oligomeric sugars are usually solubilized during steam explosion, an enzymatic hydrolysis step was required in some cases to increase the monosaccharides content. Although the presence of inhibitors released during pretreatment (e.g. formic acid) hindered hydrolysis yields, the addition of hemicellulases and the enzyme dosage optimization resulted in 85%, 89% and 95% of glucose, xylose and arabinose release from soluble oligomers, respectively. Lactobacillus pentosus CECT4023T was used for lactic acid fermentation of C6 and C5 sugars from the hydrolysate with the highest sugars concentration, that did not require enzymatic hydrolysis. Xylose consumption was hampered due to the inhibitory effect of acids that produced pH drop. Different pH control systems were applied and automatic NaOH addition in bioreactor resulted in 21 g L−1 of lactic acid (95% of the maximum theoretical yield) that implied 44% increase in lactic acid production when compared with flask fermentation. These results provide new insights for the valorisation of emerging lignocellulosic materials like gardening residues into high added-value products.

One-factor-at-a-time and response surface statistical designs for improved lactic acid production from beet molasses by Enterococcus hirae ds10

In this study, the production of lactic acid (LA) from beet molasses, a by-product of the beet sugar industry was investigated using newly isolated potential lactic acid bacteria. Isolate ds10 was selected amongst 138 bacterial isolates obtained from natural sources. This isolate was identified as Enterococcus hirae ds10 based on morphological, biochemical and molecular characteristics using 16S rRNA sequence. Direct utilization of molasses achieved low LA production at 2.01 g L‒1. Different molasses’ pretreatment methods were investigated. Molasses treated with EDTA were considered as the best substrate achieving effective LA production at 11.39 ± 2.07 g L‒1. Furthermore, medium constituent was optimized, where supplementation of 0.5% (w/v) ammonium chloride and 0.05% (w/v) yeast extract exhibited the best fermentation medium. Further optimization of fermentation factors was performed by using one-factor-at-a-time (OFAT) and response surface Minitab 18 software approaches. OFAT technique achieved the maximum LA production of 25.4 ± 0.42 g L‒1 after 24 h at sugar molasses conc., 4% (w/v); inoculum size, 10% (v/v); pH, 8.0; and temperature, 40 °C. Whereas, response surface Minitab 18 software approach resulted in a 60% increase in LA production achieving 40.69 g L‒1 at 60 g L‒1 sugar concentration, 0.625 g L‒1 yeast extract, 40 °C, pH 8 and 9.5% inoculum size. The optimization strategy in this study could achieve a 20-fold increase in LA production as compared to initial production.

High Improvement in Lactic Acid Productivity by New Alkaliphilic Bacterium Using Repeated Batch Fermentation Integrated with Increased Substrate Concentration.

Optically pure lactic acid (LA) is an important chemical platform that has a wide range of industrial and biotechnological applications. Improved parameters for cost effective LA production are of great interest for industrial developments. In the present study, an alkaliphilic lactic acid bacterium, BoM 1-2, was selected among 369 newly obtained bacterial isolates. It was characterized using API 50 CHL kit and identified as Enterococcus hirae BoM 1-2 by 16S rRNA gene sequence analysis. Efficient polymer-grade L-lactic acid production was achieved at pH 9.0 and 40°C. In batch fermentation strategy using 20 g L−1 glucose, 19.6 g L−1 lactic acid was obtained with volumetric productivity of 2.18 g L−1 h−1. While using 100 g L−1 glucose, 96.0 g L−1 lactic acid was obtained with volumetric productivity of 1.07 g L−1 h−1. The highest lactic acid concentration of 180.6 g L−1 was achieved in multipulse fed batch strategy with volumetric productivity of 0.65 g L−1 h−1. To achieve higher productivity, repeated fermentation processes were applied using the two different strategies. In the first strategy, the lactic acid productivity was increased from 1.97 g L−1 h−1 to 4.48 g L−1 h−1 when the total of 10 repeated runs were carried out using 60 g L−1 glucose, but lactic acid productivity decreased to 2.95 g L−1 h−1 using 100 g L−1 glucose. In second strategy, repeated fermentation coupled with gradual increase in glucose concentration from 40 to 100 g L−1 was conducted for 24 runs. A dramatic increase in LA productivity up to 39.9 g L−1 h−1 (18-fold compared to first run) was achieved using 40 g L−1 glucose while volumetric productivity ranging between 24.8 and 29.9 g L−1 h−1 was achieved using 60–100 g L−1 glucose.

Greener L-lactic acid production through in situ extractive fermentation by an acid-tolerant Lactobacillus strain.

Lactic acid (LA) fermentation requires a neutralizer for a physiologically acceptable range. However, a neutralizer generates a large amount of gypsum, an environmental pollutant. Furthermore, the downstream processing is complicated and expensive, comprising 50-70% of the total cost. We previously developed a Lactobacillus delbrueckii FM1, which can produce undissociated LA without neutralizer. Here, we improved FM1 by adaptive evolution at pH4.5, which generated Adp FM1 showing an ~ 1.80-fold increase in LA production compared to FM1. The LA production via fed-batch fermentation yielded 36.2g/L of LA, with a productivity of 0.500g/L/h. However, cell viability was reduced due to the acidic pH and/or end-product inhibition. Therefore, an in situ LA recovery process using an extractive solvent was employed to maintain cell viability. Adp FM1 produced 49.2g/L of LA via in situ LA-extractive fed-batch fermentation, which was ~ 1.4-fold higher than that without LA extraction. Adp FM1 provided a total LA productivity of 0.512g/L/h in 96h. Among the tested strains, Adp FM1 exhibited the highest H+-ATPase activity and a 415-fold increase in H+-ATPase gene expression compared to the parent strain. These results suggest that the in situ LA extractive fermentation process will ease downstream processing and prove to be a more economical and environmentally friendly option compared to the present fermentation. To our knowledge, this is the first report on the production of undissociated L-LA by Lactobacillus using an in situ recovery process, with high LA production levels and productivity.

Fermenting Saudi Wasted Dates by Using &amp;lt;i&amp;gt;Lactobacillus casei&amp;lt;/i&amp;gt; (ATCC 393), &amp;lt;i&amp;gt;Acidophilus&amp;lt;/i&amp;gt; (CICC 6088) and the Mixed-Culture Bacteria to Produce Lactic Acid

The Kingdom of Saudi Arabia produces over one million metric tons annually, which returns a 20% of wasted dates annually. Lactic acid and its derivatives are widely used in food, pharmaceutical and textile industries. There has been an increase in lactic acid production because it is used as a raw material to produce polylactic acid, a polymer that is used as a special medical and environmental friendly biodegradable plastic. This study aimed to use wasted dates to produce lactic acid by single culture Lactobacillus casei (ATCC 393), Lactobacillus acidophilus (CICC 6088) and the mixed culture using batch fermentation. The investigation results showed that the maximum concentration of lactic acid for ATCC 393, CICC 6088 and the mixed culture are 87, 84 and 84 g/l respectively. For single CICC 6088 and the mixed culture, the total percentage of glucose and fructose utilized was found to be 100%; 76%, respectively, whereas in the case of the single culture ATCC 393, the total percentage of glucose and fructose were 100% and 72%, respectively. With regard to lactic acid concentration, and sugar consumption, the results revealed that the single culture ATCC 393 produced the optimum lactic acid of 87 g/l for 48 hr with initial sugar concentration of 90 g/l.

Hydrogen and lactic acid synthesis by the wild-type and a laboratory strain of the hyperthermophilic bacterium Thermotoga neapolitana DSMZ 4359T under capnophilic lactic fermentation conditions

Thermotoga neapolitana is a hyperthermophilic eubacterium that produces hydrogen by sugar fermentation. A lab strain of T. neapolitana DSMZ 4359T maintained in a CO2-enriched atmosphere showed a stable increase of lactic acid production under capnophilic lactic fermentation (CLF) conditions. The genotypic comparison between the putative mutant (TN-CMut) and the original strain DSMZ 4359T (WT4359) revealed 88.1 (±2.4)% DNA homology. RiboPrint® and MALDI-TOF mass analyses support a genetic differentiation beyond subspecies level. The phenotypic characterization indicated a high correlation between the two strains, except for the lactic acid production. Under identical operating conditions, the lab mutant produced significantly more lactic acid than the parent strain without impairing the hydrogen yield. The highest divergence between TN-CMut and WT4359 was observed for fermentation of glucose or lactose at 80 °C. Based on these results, we propose that the lab strain is a new subspecies of the genus Thermotoga that is named T. neapolitana subsp. capnolactica with regards to its improved feature to produce lactic acid under capnophilic conditions.

문어 배추김치에서 분리한 Leuconostoc mesenteroides SK-1을 이용한 수산물김치의 제조 및 발효 특성

This study was carried out to investigate the effectiveness of Leuconostoc mesenteroides isolated from octopus baechu kimchi as a potential starter for seafood kimchi. L. mesenteroides is lactic acid bacterium currently used as a starter for kimchi production. We selected the most effective L. mesenteroides strain from the 7 strains isolated from octopus baechu kimchi and, based on biochemical properties and 16S rRNA sequencing, identified the selected strain as L. mesenteroides SK-1. The SK-1 strain exhibited acid-tolerance, good survival capacity, and excellent dextran productivity. We investigated the effects the SK-1 of starter on seafood kimchi fermentation. Octopus baechu kimchi was fermented with L. mesenteroides SK-1 at 4˚C for 35 d. The decrease in pH and increase in acidity in octopus baechu kimchi fermented with the SK-1 starter occurred more quickly than that in the control kimchi indicating that. Octopus baechu kimchi with SK-1 starter has a relatively slow rate of increase in lactic acid production. As a result, octopus baechu kimchi prepared with L. mesenteroides SK-1 can be maintained at a suitable ripening degree over an extended period of time compared to that of the control kimchi, Moreover, the octopus baechu kimchi started with L. mesenteroides SK-1 has excellent sensory properties, including a refreshing taste, and a weak sour odor.

A Comparative Study Of Probioticated Kunun-Zaki By Probiotic Strains Of Pediococci spp. And Lactobacillus rhamnosus GG

Non-dairy probiotic functional foods are receiving considerable interest recently owing to the inability to cause allergy in certain segments of the population. Studies on probiotication were carried out to determine the suitability of kunun-zaki as food matrix for production of probiotic beverage using single and mixed culture of Pediococcus acidilactici KU7, Pediococcus pentosaceus CREC5 and Lactobacillus rhamnosus GG. Probioticated and un-probioticated kunun-zaki samples were designated PKZ and UPKZ, respectively. There was a significant difference in the viable count during storage. Viable counts of the LAB strains decreased with increasing storage time with P. acidilactici KU7 having the highest viability at the beginning and end of storage (3.43 ± 0.06 and 0.93± 0.12 x108 cfu/ml). There was a decrease in pH of the PKZ samples within the 1st and 3rd week with corresponding increase in lactic acid production (71.16 ± 0.01 – 441.39 ± 0.01). Marked increase in pH and a decline in lactic acid were observed at the 4th week of storage in all samples. Total soluble solids content of the beverage was observed to decrease with increasing storage time ranging from 8.25 ± 0.01-4.97± 0.01. There was no significant difference in pH and total soluble solids of UPKZ and colour of the PKZ and UPKZ samples during storage. All the PKZ samples were able to inhibit the growth of selected pathogens with marked variability amongst the samples. The UPKZ sample also showed slight inhibitory activity. The samples showed a decline in proximate and mineral composition at the end of storage. Sensory evaluation showed the PKZ samples were preferred over the UPKZ samples. This study shows that probioticated kunun-zaki can serve as a suitable non-dairy alternative to dairy probiotic formulations and would be of health benefits to potential consumers.

Precultivation of Bacillus coagulans DSM2314 in the presence of furfural decreases inhibitory effects of lignocellulosic by-products during L(+)-lactic acid fermentation.

By-products resulting from thermo-chemical pretreatment of lignocellulose can inhibit fermentation of lignocellulosic sugars to lactic acid. Furfural is such a by-product, which is formed during acid pretreatment of lignocellulose. pH-controlled fermentations with 1 L starting volume, containing YP medium and a mixture of lignocellulosic by-products, were inoculated with precultures of Bacillus coagulans DSM2314 to which 1 g/L furfural was added. The addition of furfural to precultures resulted in an increase in l(+)-lactic acid productivity by a factor 2 to 1.39 g/L/h, an increase in lactic acid production from 54 to 71 g and an increase in conversion yields of sugar to lactic acid from 68 to 88 % W/W in subsequent fermentations. The improved performance was not caused by furfural consumption or conversion, indicating that the cells acquired a higher tolerance towards this by-product. The improvement coincided with a significant elongation of B. coagulans cells. Via RNA-Seq analysis, an upregulation of pathways involved in the synthesis of cell wall components such as bacillosamine, peptidoglycan and spermidine was observed in elongated cells. Furthermore, the gene SigB and genes promoted by SigB, such as NhaX and YsnF, were upregulated in the presence of furfural. These genes are involved in stress responses in bacilli.

Overexpression of ESBP6 improves lactic acid resistance and production in Saccharomyces cerevisiae

Polylactic acid plastics are receiving increasing attention for the control of atmospheric CO2 emissions. Lactic acid, the building block for polylactic acid, is produced by fermentation technology from renewable carbon sources. The yeast Saccharomyces cerevisiae, harboring the lactate dehydrogenases gene (LDH), produces lactic acid at a large scale due to its strong acid resistance, to its simple nutritional requirements and to its ease of genetic engineering. Since improvement of lactic acid resistance is correlated with an increase of lactic acid production under non-neutralizing condition, we isolated a novel gene that enhances lactic acid resistance using a multi-copy yeast genomic DNA library. In this study, we identified the ESBP6 gene, which increases lactic acid resistance when overexpressed and which encodes a protein with similarity to monocarboxylate permeases. Although ESBP6 was not induced in response to lactic acid stress, it caused weak but reproducible sensitivity to lactic acid when disrupted. Furthermore, intracellular pH in the ESBP6 overexpressing strain was higher than that in the wild-type strain under lactic acid stressed condition, suggesting that Esbp6 plays some roles in lactic acid adaptation response. The ESBP6 overexpressing strain carrying the LDH gene induced 20% increase in lactic acid production compared with the wild-type strain carrying the LDH gene under non-neutralizing conditions. These results indicate that overexpression of ESBP6 provides a novel and useful tool to improve lactic acid resistance and lactic acid production in yeast.

Naringin suppresses the metabolism of A375 cells by inhibiting the phosphorylation of c-Src

Elevation of glycolysis, increase in lactic acid production, and enhancement of mitochondrial biogenesis are all the changes of energy metabolism of melanoma cells. Melanoma cells' metabolism and energy production networks play an important role in cancer proliferation, survival, motility, invasiveness, metastasis, and angiogenesis. Since the Warburg theory was put forward in the 1930s, more researchers focus on finding new ways for effectively eliminating cancer cells by targeting their energy metabolism. In this study, we found naringin has the inhibitory effects on the glucose metabolism of A375 cells, a melanoma cell line, in a concentration-dependent manner. We also found that naringin could significantly reduce the phosphorylation of c-Src. In summary, we demonstrated that naringin inhibits the malignant phenotype of A375 cells by suppressing c-Src and its downstream signaling pathway. More importantly, we provide the novel mechanism that, as a natural inhibitor of c-Src, naringin could be an effective candidate for the treatment of melanoma.

Changes in SAM2 expression affect lactic acid tolerance and lactic acid production in Saccharomyces cerevisiae.

BackgroundThe great interest in the production of highly pure lactic acid enantiomers comes from the application of polylactic acid (PLA) for the production of biodegradable plastics. Yeasts can be considered as alternative cell factories to lactic acid bacteria for lactic acid production, despite not being natural producers, since they can better tolerate acidic environments. We have previously described metabolically engineered Saccharomyces cerevisiae strains producing high amounts of L-lactic acid (>60 g/L) at low pH. The high product concentration represents the major limiting step of the process, mainly because of its toxic effects. Therefore, our goal was the identification of novel targets for strain improvement possibly involved in the yeast response to lactic acid stress.ResultsThe enzyme S-adenosylmethionine (SAM) synthetase catalyses the only known reaction leading to the biosynthesis of SAM, an important cellular cofactor. SAM is involved in phospholipid biosynthesis and hence in membrane remodelling during acid stress. Since only the enzyme isoform 2 seems to be responsive to membrane related signals (e.g. myo-inositol), Sam2p was tagged with GFP to analyse its abundance and cellular localization under different stress conditions. Western blot analyses showed that lactic acid exposure correlates with an increase in protein levels. The SAM2 gene was then overexpressed and deleted in laboratory strains. Remarkably, in the BY4741 strain its deletion conferred higher resistance to lactic acid, while its overexpression was detrimental. Therefore, SAM2 was deleted in a strain previously engineered and evolved for industrial lactic acid production and tolerance, resulting in higher production.ConclusionsHere we demonstrated that the modulation of SAM2 can have different outcomes, from clear effects to no significant phenotypic responses, upon lactic acid stress in different genetic backgrounds, and that at least in one genetic background SAM2 deletion led to an industrially relevant increase in lactic acid production. Further work is needed to elucidate the molecular basis of these observations, which underline once more that strain robustness relies on complex cellular mechanisms, involving regulatory genes and proteins. Our data confirm cofactor engineering as an important tool for cell factory improvement.Electronic supplementary materialThe online version of this article (doi:10.1186/s12934-014-0147-7) contains supplementary material, which is available to authorized users.

INTEGRATED ANALYSIS IDENTIFIES DIFFERENT METABOLIC SIGNATURES WITHIN BOTH TUMOR-INITIATING CELLS AND STEM CELLS IN A MURINE GLIOBLASTOMA MODEL

BACKGROUND: The metabolic preference of malignant gliomas for glycolysis as an energy source is a potential diagnostic and therapeutic target. As a result of the cellular heterogeneity of these tumors, however, the relation between glycolytic preference, tumor formation and tumor maintenance has remained unknown. To address this issue, we analyzed the metabolic profiles of isogenic glioma-initiating cells (GICs) and glioma stem cells (GSCs) in a syngeneic mouse model. METHODS: GICs were established by overexpression of H-RasV12-dsRed in Ink4a/Arf–null neural stem cells. Subpopulations of GICs were obtained by single-cell cloning, and clones differing in extracellular acidification potential were used for quantification of intracellular metabolites and related enzymes. Tumors formed after intracranial implantation of the GIC clones in mice were examined for pathological features of glioma and expression of glycolytic enzymes. GSCs were established by sphere culture of dsRed-positive cells from the primary tumors and assessed for metabolic characteristics. RESULTS: Malignant transformation of neural stem cells resulted in a distinct shift in metabolism, with a significant increase in lactic acid production as the most pronounced characteristic of all malignant cells. Interestingly however, both GICs and GSCs could adopt two different metabolic profiles. Some clones displayed high glucose consumption and lactate production, while others consumed more oxygen, produced more ATP and had a higher respiratory capacity. The glycolytic clones exhibited higher levels of key glycolytic enzymes such as hexokinase 2 and pyruvate kinase M2, and the clones relying on oxidative phosphorylation had lower levels of pyruvate dehydrogenase kinase 1. While all GICs had equal tumorigenic ability, the differential expression of the metabolic enzymes persisted in the tumors formed by these clones in vivo, as well as in the GSCs of the respective tumors. CONCLUSIONS: The metabolic characteristics of glioma cells appear early during malignant transformation and persist until the late stages of tumor formation. However, even isogenic clones may be heterogeneous in terms of metabolic features, with both GICs and GSCs being able to satisfy their bioenergetics needs not only through aerobic glycolysis, but also through oxidative phosphorylation. These results suggest that a more detailed understanding of the metabolic profile of glioma is imperative for effective diagnostic and therapeutic targeting. SECONDARY CATEGORY: n/a.