Increasing Ethanol Concentration Research Articles

Directed evolution of Saccharomyces cerevisiae for low volatile acidity during winemaking under aerobic conditions

The use of yeast respiratory metabolism has been proposed as a promising approach to solve the problem of increasing ethanol content in wine, which is largely due to climate change. The use of S. cerevisiae for this purpose is mostly hampered by acetic acid overproduction generated under the necessary aerobic conditions. However, it was previously shown that a reg1 mutant, alleviated for carbon catabolite repression (CCR), showed low acetic acid production under aerobic conditions. In this work directed evolution of three wine yeast strains was performed to recover CCR-alleviated strains, expecting they will also be improved concerning volatile acidity. This was done by subculturing strains on galactose, in the presence of 2-deoxyglucose for around 140 generations. As expected, all evolved yeast populations released less acetic acid than their parental strains in grape juice, under aerobic conditions. Single clones were isolated from the evolved populations, either directly or after one cycle of aerobic fermentation. Only some clones from one of three original strains showed lower acetic acid production than their parental strain. Most clones isolated from EC1118 showed slower growth. However, even the most promising clones failed to reduce acetic acid production under aerobic conditions in bioreactors. Therefore, despite the concept of selecting low acetic acid producers by using 2-deoxyglucose as selective agent was found to be correct, especially at the population level, the recovery of strains with potential industrial utility by this experimental approach remains a challenge.

Alcohol use trends in Dallas County during the COVID-19 pandemic

Alcohol (ethanol) is the most widely detected drug in forensic toxicology casework and an increase in consumption of alcohol was reported during the COVID-19 pandemic. The increase in consumption could be attributed to rising stress levels and social isolation. To determine whether the pandemic had an impact on ethanol positivity and concentrations in cases analyzed by the Dallas County Southwestern Institute of Forensic Sciences, blood ethanol results were evaluated from January 1, 2019, through December 31, 2021. This time frame captured ethanol prevalence and concentrations before, during, and immediately following the pandemic for comparison. The average ethanol concentration in postmortem casework over the three years for each quarter ranged from 0.116 g/100 mL to 0.142 g/100 mL while the average concentration in driving while intoxicated (DWI) was higher, ranging from 0.173 g/100 mL to 0.188 g/100 mL. The ethanol positivity rate for postmortem casework remained relatively the same at approximately 20% during the time frame, while there was a decrease in ethanol positivity rate for DWI casework during the pandemic in April - June (Q2) 2020. However, the positivity rate returned to pre-pandemic levels by the end of 2020. Despite the self-reported surveys of increased alcohol consumption during the pandemic, a corresponding increase in average ethanol concentrations was not observed in Dallas County and the surrounding area.

Efficient isolation of immunostimulatory polysaccharides from Lentinula edodes by autoclaving-ultrasonication extraction and fractional precipitation

A hyphenated process, autoclaving followed by ultrasonication (AU), was evaluated for efficient extraction of polysaccharides (PS) from Lentinula edodes (Shiitake) mushroom. The PS yield (w/w) was 8.44 % from hot-water extraction (HWE), 11.01 % by autoclaving extraction (AE), and 16.3 % by AUE. The AUE water extract was subject to fractional precipitation in four-steps with increasing ethanol concentration of 40 %, 50 %, 70 % and 80 % (v/v), yielding four PS fractions in descending molecular weight (MW), PS40 > PS50 > PS70 > PS80. All the four PS fractions were composed of four monosaccharide residues, mannose (Man), glucose (Glc) and galactose (Gal) but in different mole ratios. The PS40 fraction with the highest average MW (4.98 × 106) was the most abundant fraction, accounting for 64.4 % of the total PS mass and also had the highest glucose molar ratio (~80 %). PS40 also most significantly enhanced the NO, and ROS generation and phagocytic activity in RAW 264.7 cells. The results proved that AUE followed by fractional ethanol precipitation is an efficient strategy with reduced solvent expenditure for isolation of the major immunostimulatory PS from L. edodes mushroom.

The function of ethanol in olfactory associative behaviors in Drosophila melanogaster larvae.

Drosophila melanogaster larvae develop on fermenting fruits with increasing ethanol concentrations. To address the relevance of ethanol in the behavioral response of the larvae, we analyzed the function of ethanol in the context of olfactory associative behavior in Canton S and w1118 larvae. The motivation of larvae to move toward or out of an ethanol-containing substrate depends on the ethanol concentration and the genotype. Ethanol in the substrate reduces the attraction to odorant cues in the environment. Relatively short repetitive exposures to ethanol, which are comparable in their duration to reinforcer representation in olfactory associative learning and memory paradigms, result in positive or negative association with the paired odorant or indifference to it. The outcome depends on the order in which the reinforcer is presented during training, the genotype and the presence of the reinforcer during the test. Independent of the order of odorant presentation during training, Canton S and w1118 larvae do not form a positive or negative association with the odorant when ethanol is not present in the test context. When ethanol is present in the test, w1118 larvae show aversion to an odorant paired with a naturally occurring ethanol concentration of 5%. Our results provide insights into the parameters influencing olfactory associative behaviors using ethanol as a reinforcer in Drosophila larvae and indicate that short exposures to ethanol might not uncover the positive rewarding properties of ethanol for developing larvae.

Molecular dynamics simulations of water-ethanol droplet on silicon surface

Abstract Molecular dynamics simulations are used to explore the wetting behavior of a water-ethanol droplet on the silicon surface. The effect of ethanol concentration on the wettability of a water-ethanol droplet on the silicon surface was analysed by calculation of contact angle. At 30% ethanol concentrations, the water contact angle was 50.7°, while at 50% ethanol concentrations, it was 36°. The results showed that the contact angle of a droplet on a silicon surface decreases with increasing ethanol concentrations. The formation of hydrogen bonds (HBs) between water-water molecules was 677 for the 30% ethanol system, while at 50% ethanol concentrations, it was 141. The number of hydrogen bonds between water molecules reduces as the ethanol concentrations rise. The HBs between water molecules and the silicon surface is seen to grow as the ethanol concentration rises. The overall potential energies of pure water, 7:3 water-ethanol, and 1:1 water-ethanol systems are −74.4, −96.16, and −158.59 kcal/mol, respectively. The contact angle and number density of water molecules on the surface of the silicon revealed that at different ethanol concentrations, more water molecules are distributed on the silicon surface.

Effects of intramolecular oxygen and partial premixing on soot formation in ethane/ethanol flames

Detailed soot concentration and temperature fields were measured in coflow laminar diffusion flames of neat ethane and ethane/ethanol mixtures, and partially premixed flames of ethane/ethanol mixtures. Two-dimensional diffuse-light line-of-sight attenuation and spectral soot emission techniques were employed for soot volume fraction and temperature measurements, respectively. The choice of flow rates prioritized tractability and comparability between flames. To this end, the total carbon mass flow rate and the C/H ratio were kept constant for all ethane/ethanol mixture flames, i.e., oxygen was introduced into the fuel stream either as intramolecular oxygen in ethanol or both as intermolecular and molecular oxygen. Soot concentration was observed to decrease monotonically with an increasing ethanol content in ethane/ethanol mixtures without synergistic effects. Soot concentration was also measured in neat ethane flames with flow rates matching those of ethane in ethane/ethanol mixtures. A comparison of these flames with ethane/ethanol flames revealed a striking soot suppression effect by ethanol addition. Although the carbon flow rate was less in neat ethane flames than the total carbon flow rate of their corresponding ethane/ethanol flames, the peak soot volume fractions were significantly higher in neat ethane flames. This points to a chemical soot suppression effect beyond that can be explained by the lower sooting propensity of ethanol fuel. These results were discussed in light of the synergistic effect studies in the literature. Lastly, measurements from partially-premixed ethane/ethanol mixtures are reported. The increased oxygen content significantly increased the peak soot volume fraction in these flames. These results support that intermolecular oxygen in ethanol and molecular oxygen in the fuel tube behave drastically differently in an ethane base flame. Ethanol addition does not exhibit synergistic effects on soot formation, whereas molecular oxygen addition increases maximum soot concentration, indicating the activation of unique soot production pathways.

Effect of Ethanol Added to Diesel Fuel on the Range of Fuel Spray

The constantly growing number of vehicles sold and operated has resulted in greater contribution of automobiles to global pollution. One way to reduce emissions of carbon dioxide (CO2) and toxic compounds, including the particulates and nitrogen oxides (NOx) contained in exhaust gases, is to use alternative fuels. Within this group of fuels, those of plant origin, mainly alcohols, are attracting more and more attention because of their high oxygen content (around 35%), low viscosity, and good atomisation. However, alternative fuels have different physicochemical properties than diesel fuel, and these may affect the formation of the fuel spray, which, in turn, impacts the operation of the internal combustion engine, operating parameters, and the purity of the exhaust gases emitted into the environment. To make sure this type of fuel can be used in compression ignition engines, it is necessary to gain a thorough understanding of the phenomena and relationships occurring during fuel injection. The study investigated the effect of ethanol added to diesel fuel on the range of fuel spray. Firstly, the kinematic viscosity was determined for diesel fuel, and for diesel–ethanol blends with varying proportional contents of ethanol, up to 30% v/v. The viscosity test was carried out at 40 °C in compliance with the normative requirements. At the next stage, the range of the spray tip was measured for the same fuels in which kinematic viscosity was assessed. A visualisation chamber and a high-speed camera were applied for this purpose. The test was carried out under reproducible conditions, in line with the test methodology used to determine the range of fuel spray. The analyses assessed the effect of ethanol addition on kinematic viscosity and the range of fuel spray. The findings show that the increase in ethanol content corresponds to a decrease in kinematic viscosity by about 4% on average. The results were inconclusive for the lowest injection pressure tested (75 MPa), since some of the mixtures investigated were found with a lower spray range, compared to diesel fuel with no ethanol added. The greatest increase in the spray range (by approximately 39%) was found in the fuel with 30% content of ethanol at an injection pressure of 125 MPa.

Breeding of Fructilactobacillus sanfranciscensis with excellent ethanol tolerance based on adaptive evolution technology

AbstractFructilactobacillus (F.) sanfranciscensis LS1 is one of the dominant strains in sourdough. Ethanol produced during fermentation is an inevitable stress factor for this stain. At present, the research on the mechanism of ethanol stress in lactic acid bacteria is limited compared to yeast species (particularly Saccharomyces (S.) cerevisiae). In this study microbial physiology and protein expression analysis technology was used. F. sanfranciscensis LS1 served as the original bacteria, and evolutionary bacteria LS1‐1 were obtained by adaptive evolution. The comparison of the two strains' growth, survival rate, morphology, hydrophobicity, cohesive force and protein expression revealed that the evolved bacteria had a significantly higher ethanol tolerance than the original bacteria. Similarly, the hydrophobicity of evolved bacteria was increased about 6.6 times than that of the original bacteria. With an increase in ethanol concentration, the level of damage on evolved bacteria was less, and the total proportion of damaged cells decreased. After 8 h of culturing, the self‐cohesion of the evolved strain was 1.29 times more than the original strain. Sodium dodecyl‐sulfate polyacrylamide gel electrophoresis analysis has shown that the number of protein bands of the evolved bacteria LS1‐1 increased significantly, indicating that the associated proteins were expressed more and the strain's ability to resist environmental pressure was improved.

EXTRACTION OF CADMIUM (II), COMPLEX WITH 2- MERCAPTOBENZOTHIAZOLE AND ITS STABILITY REGARDING GAMMA RAYS AND STUDY OF BIOLOGICAL ACTIVITY OF THE COMPLEX

The study in volve the temperature effect on the extraction process for some chelate systems through study of extraction of Cd (II) by 2- mercaptobenzothiazole. The work include the calculations of thermodynamics parameters (_Hex, _Gex , _Sex) for the extraction processes to Cd (II). The results were indicated that _Hex has a negative value (exothermic process). The obtained negative values of _G ex indicated to the spontaneous extraction processes. The results were shown that D values decrease with increase of temperature while D increase with increase of ethanol concentration as catalyst. Mole ratio method was employed for expected determination of the stoichiometry of the complex. The results showed that the ratio of Cd (II) to the reagent is ( 1 : 2) respectively.

Effect of kuratsuki Kocuria on sake brewing in different koji conditions.

Koji is made using steamed rice and a koji mold, which plays an essential role in sake brewing. We challenge to build a new sake brewing method using the kuratsuki bacteria that have inhabited each sake brewery. In this paper, effects of the kuratsuki Kocuria strain TGY1127_2 were estimated on sake brewing in different koji conditions. Sake was produced by incubation of a mixture solution of koji, water, and sake yeast (strain K1401) with and without the kuratsuki Kocuria TGY1127_2. The effects of the kuratsuki Kocuria on the taste of the sake differed among different koji. The kuratsuki Kocuria led to an increase in ethanol concentration. Additionally, the sugar content (Brix) and acidity of the sake increased in proportion to the amount of koji. These results strongly suggest that the kuratsuki Kocuria does not adversely affect the fermentation activity of the sake yeast. Thus, the kuratsuki Kocuria had different effects on the taste of sake among different koji but the fermentation activity of the sake yeast was maintained.

Two-phase dual-signal-readout immunosensing platform based on multifunctional carbon nano-onions for ovarian cancer biomarker detection.

In order to detect early tumor markers and gain valuable time for treatment, there is an urgent need to develop a fast, cheap, and ultrasensitive multi-reading sensing platform. Herein, a solid/liquid two-phase dual-output biosensor was explored based on a sensitized sonochemiluminescence (SCL) strategy and a multifunctional carbon nano-onion (CNO) probe. It is clear that ultrasonic radiation caused the formation of hydroxyl radicals (˙OH), triggering the SCL signal of the emitter lucigenin (Luc2+). Meanwhile, titanium carbide nanodots and ethanol were used to enhance the SCL signal, and an astonishingly linear enhancement of the SCL intensity was produced with increasing ethanol concentration. More importantly, the CNOs, with their excellent photothermal properties and adsorption capacity, can output both the temperature signal and an enhanced SCL strength from the solid-liquid phase. Through inter-calibration of the signals from the two-phases, this biosensor shows excellent analytical performance for the detection of the ovarian cancer biomarker, human epididymis-specific protein 4, from 10-5 to 10 ng mL-1 with a low detection limit of 3.3 fg mL-1. This work not only provides a novel two-phase signal-output mode that broadens the scope of multiperformance joint applications of CNOs, but also enriches the quantitative detection of point-of-care testing.

Effects of adding different quantities of yeast and chokeberry juice on fermentation of mead

Honey is a product of high nutritional value, used as a raw material for obtaining mead. However, adding fruit juices, including chokeberry juice, can improve mead quality. This paper aims to assess the effects that adding different quantities of chokeberry juice, with the variation of 3 amounts of inoculated yeast, has on the fermentation and physicochemical, antioxidant, and antimicrobial properties of mead. The parameters analyzed are the dry matter content, pH value, and content of volatile acids, ethanol and methanol, total phenols and flavonoids, FRAP, DPPH, and ABTS tests, and antimicrobial properties. The results obtained in this paper show that adding chokeberry juice improves the antioxidant properties of the final product and positively affects the course of mead fermentation, i.e., it has led to an increase in the maximum concentration of ethanol. Regarding the chemical composition of mead, there is no significant difference, except in the obtained ethanol content, which is the highest in samples with 10% of added chokeberry juice. Furthermore, the control sample showed the best antimicrobial activity, while the sample with 5% added chokeberry juice showed the weakest effect. Finally, the strongest effect was seen in the sample with 20% of added chokeberry juice.

PRODUCTION OF BIOETHANOL FROM SUGARCANE BAGASSE THROUGH HYDROLYSIS AND FERMENTATION: THE EFFECT OF FE2+ AND CA2+ IONS ADDITION ON BIOETHANOL CONCENTRATION

Fossil energy sources are one of the driving factors in the economic development and prosperity of the nation. The availability of fossil energy sources is currently shrinking and is expected to run out quickly, so an alternative is needed to replace it. Sugarcane bagasse is a lignocellulosic biomass which can be utilized for bioethanol production as an alternative energy source. Lignocellulosic hydrolysis with the addition of H2SO4 catalyst was carried out to obtain glucose. The addition of Fe2+ and Ca2+ ions was performed to increase the glucose concentration. Commonly, Saccharomyces cerevisiae is used to convert glucose into bioethanol using fermentation process. The objective of this study was to investigate the effect of Fe2+ and Ca2+ ions on reducing sugar concentration, and the concentration of distillate bioethanol. The effect of yeast type on the concentration of bioethanol was also discussed in this paper. The result shows that the addition of Fe2+ and Ca2+ ions in the hydrolysis process can increase the concentration of glucose produced. This is because the higher concentration of cellulose, the more substrate is converted into reducing sugars. The use of Fe2+ and Ca2+ ions in the fermentation process will increase ethanol concentration compares with fermentation without metal ions. This is because Ca2+ ions have an important role in the flocculation process of bioethanol fermentation and Fe2+ ions are important nutrients for eukaryotes, which play a role in cell oxidationreduction reactions. The type of yeast that can produce higher concentrations of ethanol is tapai yeast. This is because tapai’s yeast has three supporting ingredients for the fermentation process, whereas baker’s yeast only contains two microorganisms.

Unraveling the hydrophobic interaction mechanisms of hydrocarbon and fluorinated surfaces

HypothesisNumerous hydrocarbon and fluorine-based hydrophobic surfaces have been widely applied in various engineering and bioengineering fields. It is hypothesized that the hydrophobic interactions of hydrocarbon and fluorinated surfaces in aqueous media would show some differences. ExperimentsThe hydrophobic interactions of hydrocarbon and fluorinated surfaces with air bubbles in aqueous solutions have been systematically and quantitatively measured using a bubble probe atomic force microscopy (AFM) technique. Ethanol was introduced to water for modulating the solution polarity. The experimental force profiles were analyzed using a theoretical model combining the Reynolds lubrication theory and augmented Young-Laplace equation by including disjoining pressure arisen from the Derjarguin-Landau-Verwey-Overbeek (DLVO) and non-DLVO interactions (i.e., hydrophobic interactions). FindingsThe experiment results show that the hydrophobic interactions were firstly weakened and then strengthened by increasing ethanol content in the aqueous media, mainly due to the variation in interfacial hydrogen bonding network. The fluorinated surface exhibited less sensitivity to ethanol than hydrocarbon surface, which is attributed to the presence of ordered interfacial water layer. Our work reveals the different hydrophobic effects of hydrocarbon and fluorinated surfaces, with useful implications on modulating the interfacial interactions of relevant materials in various engineering and bioengineering applications.

Response surface optimization of product yields and biofuel quality during fast hydrothermal liquefaction of a highly CO2-tolerant microalgae

The effects of biochemical components and processing variables (e.g., temperatures, solid-liquid ratio, ethanol concentration, and time) during fast hydrothermal liquefaction of a highly CO2-tolerant microalgae (Micractinium sp.) on the product yields and biofuel quality were explored using response surface methodology coupled with central composite design. Results showed that the maximum bio-oil yield (51.4 %) was obtained at 321 °C for 49 min at ethanol concentration of 75 % and solid-liquid ratio of 15.3 %. Among different studied parameters, ethanol concentration showed the highest significant impact on the bio-oil yield due to the low P-value and high F-value in ANOVA analysis. Furthermore, the chemical compositions of bio-oils were determined, which showed that the increase of ethanol concentration in the solvent not only increased the bio-oil yield but also promoted the bio-oil quality by reduction of carboxylic acids and nitrogen-containing compounds with simultaneous enhancement of esters in the bio-oil. The present results show that fast hydrothermal liquefaction is a promising approach to convert the microalgae into high quality biofuels rich in esters.

Pressurized liquid extraction of compounds from Stevia leaf: Evaluation of process variables and extract characterization

The extraction of compounds from Stevia rebaudiana leaves under pressurized conditions was investigated. The effect of the ethanol percentage in the extracting solvent, static time, pressure and temperature on global extraction yield (YGE), total phenolic content (TPC) and antioxidant activity (AA) was evaluated. The extract from pressurized liquid extraction (PLE) was characterized and compared to that obtained from Soxhlet and ultrasound-assisted extraction (UAE). It appears that the increase of ethanol concentration in the solvent favored response variables, while the increase in static time and pressure did not affect the extraction. The temperature (125 ºC) provided an increase in YGE and the highest levels of active compounds were obtained after using 70% (v/v) ethanol in the extracting solvent (15 mL g−1) and 30 min. The different techniques evaluated provided similar YGE, while PLE providing greater extraction of TPC and AA, and Soxhlet favored the extraction of steviol glycosides and total flavonoids.

Impact of fuel ethanol content on regulated and non-regulated emissions monitored by various analytical techniques over flex-fuel and conversion kit applications

This study evaluates the impact of ethanol content on both regulated and non-regulated emissions with recent vehicle technologies. The three vehicles used here are complying with Euro 6d-temp or Euro 6c emission standards and are adapted to variable ethanol concentrations, either through flex-fuel or E85 conversion kit. Both regulated and non-regulated emissions are characterized to highlight the fuel and vehicle technology impacts. The analysis of non-regulated pollutants in exhaust gases is performed with three different techniques to evaluate their advantages or limitations and assess time-resolved emission levels. HPLC coupled to UV detection to measure aldehydes and ketones. GC–MS was used for PAHs characterization. GC-FID was used to measure VOCs (C1 to C12) on the first phase of the WLTC. FTICR-MS was used to assess time-resolved emission levels. Results indicate a negligible impact on the emissions for ethanol content from 10 to 20% vol. Nevertheless, a significant emission composition variation is observed at 50% vol., and this is even more pronounced with 85% vol. of ethanol. Expected trends based on the literature review are confirmed for all vehicles and this includes an increase in unburned ethanol and aldehydes emissions with higher ethanol content while in this condition lower aromatics contribute to reduce particulate matters emissions. The use of varying amounts of ethanol in recent and diverse Euro 6d-temp vehicle technologies shows that the increase in ethanol content is unaffected by the reduction in particulate emissions and the increase in the finest. However, the results indicate a risk of increased NOx emissions for Euro 6d-temp IC engines, which should be confirmed on other vehicles of similar technology. This study results also indicate that most pollutants are emitted in the engine and exhaust warm-up phase. All analytical techniques exhibited similar trends.

A Study on the Whitening and Anti-Wrinkle Effects of Red Sword Bean Extract in Functional Cosmetics for Skin Care

In this study, to analyze and determine the bioactive compounds of red sword bean as natural ingredients for functional cosmetics, hot water extraction was performed with ethanol contents of 20%, 50%, and 80%. In addition, for the respective extracts, a gas chromatography-mass spectrometry (GC-MS) analysis for the determination of bioactive compounds and liquid chromatography-mass spectrometry (LC-MS) analysis for the determination of polyphenol and flavonoid contents were performed along with the determination of antioxidant capacity. Moreover, experiments were performed to test the skin whitening and anti-wrinkle effects; a cytotoxicity evaluation was also conducted. As a result of the colorimetric assay, the lightness (L) value decreased with increasing ethanol content, whereas the redness (a*) and yellowness (b*) values tended to increase. This is presumed to be because the active compounds of the double bond structure increased as the ethanol content increased. As a result of GC-MS analysis to determine chemical composition, the detection of ethyl gallate, an antioxidant, and mandelic acid, an active compound with whitening and wrinkle improvement effects, was confirmed; the detected concentrations increased with increasing ethanol content. In the experiment to examine the antioxidant effect of red sword bean extract, the IC50 value of the 80% ethanol extract showed a high antioxidant capacity comparable to that of the control, ascorbic acid. As a result of the tyrosinase inhibitory activity assay, the highest inhibition (%) was confirmed at 80% ethanol content. Furthermore, in the collagenase inhibitory activity assay, all extracts showed high collagenase inhibitory activity of over 90%. Specifically, at 20% ethanol content, a higher inhibition (%) was confirmed than that of the control, ascorbic acid.

RNA-seq based transcriptomic analysis of the non-conventional yeast Spathaspora passalidarum during Melle-boinot cell recycle in xylose-glucose mixtures

The Melle-Boinot is a promising process for second-generation ethanol production by xylose-fermenting yeasts. However, the impact of this process on the physiology of the non-conventional yeast Spathaspora passalidarum during second-generation ethanol production remains unclear. Therefore, we performed a transcriptomic analysis of S. passalidarum to determine the differences and global responses of differentially expressed genes (DEGs) during five fed-batch fermentations with cell recycle. A cycle-to-cycle metabolic reprogramming was observed resulting in an increase in ethanol yield (32%), volumetric productivity (33%), and titer (33%); and an expressive decrease of 94% of xylitol production. A broad set of pathways operated synergically such as fatty acid metabolism, N-glycan biosynthesis, glyoxylate and dicarboxylate metabolism, oxidative phosphorylation, glutathione metabolism and sulfur metabolism, indicating those as important mechanisms for cell recycling adaptations due to increased ethanol concentration, long-term ethanol exposure and osmotic stress. Together these results suggest that cellular energy was redirected towards the production of cell wall components enabling S. passalidarum cells to thrive on consecutive recycles. Furthermore, these results are instrumental to guide genetic-engineering efforts of xylose-fermenting yeasts to improve the productiveness and feasibility of renewable energy production from lignocellulosic biomass and hemicellulosic hydrolysates.

Ethanol-lactate transition of Lachancea thermotolerans is linked to nitrogen metabolism

Climate change increases sugar content in grapes, resulting in unwanted increase in ethanol content of wine. Lachancea thermotolerans ferments glucose and fructose into both ethanol and lactate, decreasing final ethanol content and positively affecting wine acidity. Reported Lachancea thermotolerans strains show big variation in lactate production during fermentation. However, a mechanistic understanding of this lactate producing phenotype is currently lacking. Through a combination of metabolomics, transcriptomics, genomics and computational methods we show that the lactate production is induced by amino acid limitation in a high lactate producing strain. We found in fermentations in synthetic grape juice media that lactate production starts in the last stages of growth, marked by decreased growth rate and increased expression levels of stress related genes. This onset of lactate production is specific for the high lactate producing strain and independent of oxygen availability. The onset of lactate production was changed by increased amino acid content of the media, and it is shown by both computational methods and amino acid measurements that at the onset of lactate production amino acids become limiting for growth. This study shows that lactate production of Lachancea thermotolerans is directly linked to nitrogen availability in the media, an insight that can further aid in the improvement of wine quality.