First- and second-generation integrated process for bioethanol production: Fermentation of molasses diluted with hemicellulose hydrolysate by recombinant Saccharomyces cerevisiae.

The integration of first- (1G) and second-generation (2G) ethanol production by adding sugarcane juice or molasses to lignocellulosic hydrolysates offers the possibility to overcome the problem of inhibitors (acetic acid, furfural, hydroxymethylfurfural and phenolic compounds), and add nutrients (such as salts, sugars and nitrogen sources) to the fermentation medium, allowing the production of higher ethanol titers. In this work, an 1G2G production process was developed with hemicellulosic hydrolysate (HH) from a diluted sulfuric acid pretreatment of sugarcane bagasse and sugarcane molasses. The industrial Saccharomyces cerevisiae CAT-1 was genetically modified for xylose consumption and used for co-fermentation of sucrose, fructose, glucose, and xylose. The fed-batch fermentation with high cell density that mimics an industrial fermentation was performed at bench scale fermenter, achieved high volumetric ethanol productivity of 1.59 g L-1 h-1, 0.39 g g-1 of ethanol yield, and 44.5 g L-1 ethanol titer, and shown that the yeast was able to consume all the sugars present in must simultaneously. With the results, it was possible to establish a mass balance for the global process: from pretreatment to the co-fermentation of molasses and HH, and it was possible to establish an effective integrated process (1G2G) with sugarcane molasses and HH co-fermentation employing a recombinant yeast.

Improved biohydrogen production by co-fermentation of corn straw and excess sludge: Insights into biochemical process, microbial community and metabolic genes.

The global climate change mainly caused by fossil fuels combustion promotes that zero-carbon hydrogen production through eco-friendly methods has attracted attention in recent years. This investigation explored the biohydrogen production by co-fermentation of corn straw (CS) and excess sludge (ES), as well as comprehensively analyzed the internal mechanism. The results showed that the optimal ratio of CS to ES was 9:1 (TS) with the biohydrogen yield of 101.8 mL/g VS, which was higher than that from the mono-fermentation of CS by 1.0-fold. The pattern of volatile fatty acids (VFAs) indicated that the acetate was the most preponderant by-product in all fermentation systems during the biohydrogen production process, and its yield was improved by adding appropriate dosage of ES. In addition, the content of soluble COD (SCOD) was reduced as increasing ES, while concentration of NH4+-N showed an opposite tendency. Microbial community analysis revealed that the microbial composition in different samples showed a significant divergence. Trichococcus was the most dominant bacterial genus in the optimal ratio of 9:1 (CS/ES) fermentation system and its abundance was as high as 41.8%. The functional genes prediction found that the dominant metabolic genes and hydrogen-producing related genes had not been significantly increased in co-fermentation system (CS/ES = 9:1) compared to that in the mono-fermentation of CS, implying that enhancement of biohydrogen production by adding ES mainly relied on balancing nutrients and adjusting microbial community in this study. Further redundancy analysis (RDA) confirmed that biohydrogen yield was closely correlated with the enrichment of Trichococcus.

Effect of Hanseniaspora vineae and Saccharomyces cerevisiae co-fermentations on aroma compound production in beer.

In recent years, the boom of the craft beer industry refocused the biotech interest from ethanol production to diversification of beer aroma profiles. This study analyses the fermentative phenotype of a collection of non-conventional yeasts and examines their role in creating new flavours, particularly through co-fermentation with industrial Saccharomyces cerevisiae. High-throughput solid and liquid media fitness screening compared the ability of eight Saccharomyces and four non-Saccharomyces yeast strains to grow in wort. We determined the volatile profile of these yeast strains and found that Hanseniaspora vineae displayed a particularly high production of the desirable aroma compounds ethyl acetate and 2-phenethyl acetate. Given that H. vineae on its own can't ferment maltose and maltotriose, we carried out mixed wort co-fermentations with a S. cerevisiae brewing strain at different ratios. The two yeast strains were able to co-exist throughout the experiment, regardless of their initial inoculum, and the increase in the production of the esters observed in the H. vineae monoculture was maintained, alongside with a high ethanol production. Moreover, different inoculum ratios yielded different aroma profiles: the 50/50 S. cerevisiae/H. vineae ratio produced a more balanced profile, while the 10/90 ratio generated stronger floral aromas. Our findings show the potential of using different yeasts and different inoculum combinations to tailor the final aroma, thus offering new possibilities for a broader range of beer flavours and styles.

Analysis of landfill leachate promoting efficient application of weathered coal anaerobic fermentation.

This research aimed to develop a new method for clean utilization and treatment of landfill leachate and solid waste weathered coal. Landfill leachate and weathered coal were adopted for combined anaerobic fermentation for methane production. The characteristics of microbial community, mechanism of biological methane production, and utilization characteristics of fermentation broth and solid residue for co-fermentation were analyzed through metagenomics, soluble organic matter detection and thermogravimetric (TG) analysis. The obtained results revealed that combined anaerobic fermentation increased methane production by 80.1%. Syntrophomonas, Salipiger, Methanosaeta and Methanothrix were highly correlated. Gene abundances of 2-oxoacid ferredoxin oxidoreductase and enolase were increased in methane conversion pathway mainly by acetic acid. Pyruvate-ferroredoxin oxidoreductase, 2-oxoglutarate synthase and succinate dehydrogenase acetate synthase intensified electron transfer pathways among microorganisms. Fulvic acid, tyrosine and tryptophan contents were high in fermentation broth. Volatile decomposition temperature, ignition point and residual char combustion temperature of residual coal were decreased and combustion was more stable. The obtained results showed that the co-fermentation of landfill leachate and weathered coal improved biological methane gas production, degraded weathered coal and improved combustion performance, which provided a new idea for weathered coal clean utilization.

Study on the mechanism of action of methane production by co-fermentation of sludge and lignite.

To improve the methanogenic efficiency of lignite anaerobic fermentation and explore innovative approaches to sludge utilization, a co-fermentation technique involving lignite and sludge was employed for converting biomass into biomethane. Volatile suspended solids were introduced as a native enrichment of the sludge and mixed with lignite for fermentation. The synergistic fermentation mechanism between sludge and lignite for biomethane production was analyzed through biochemical methane potential experiments, measurement of various parameters pre- and post-fermentation, observation of bacterial population changes during the peak of reaction, carbon migration assessment, and evaluation of rheological characteristics. The results showed that the addition of sludge in the anaerobic fermentation process improved the microorganisms' ability to degrade lignite and bolstered biomethane production. Notably, the maximum methane production recorded was 215.52 mL/g-volatile suspended solids, achieved at a sludge to coal ratio of 3:1, with a synergistic growth rate of 25.37%. Furthermore, the removal rates of total suspended solids, and total chemical oxygen demand exhibited an upward trend with an increasing percentage of sludge in the mixture. The relative abundance and activity of the methanogens population were found to increase with an appropriate ratio of sludge to lignite. This observation confirmed the migration of carbon between the solid-liquid-gas phases, promoting enhanced system affinity. Additionally, the changes in solid-liquid phase parameters before and after the reaction indicated that the addition of sludge improved the system's degradation capacity. The results of the study hold significant implications in realizing the resource utilization of sludge and lignite while contributing to environmental protection endeavors.

Enzyme enhanced lactic acid fermentation of swine manure and apple waste: Insights from organic matter transformation and functional bacteria.

Anaerobic co-fermentation is a favorable way to convert agricultural waste, such as swine manure (SM) and apple waste (AW), into lactic acid (LA) through microbial action. However, the limited hydrolysis of organic matter remains a main challenge in the anaerobic co-fermentation process. Therefore, this work aims to deeply understand the impact of cellulase (C) and protease (P) ratios on LA production during the anaerobic co-fermentation of SM with AW. Results showed that the combined use of cellulase and protease significantly improved the hydrolysis during the enzymatic pretreatment, thus enhancing the LA production in anaerobic acidification. The highest LA reached 41.02 ± 2.09 g/L within 12 days at the ratio of C/P = 1:3, which was approximately 1.26-fold of that in the control. After a C/P = 1:3 pretreatment, a significant SCOD release of 45.34 ± 2.87 g/L was achieved, which was 1.13 times the amount in the control. Moreover, improved LA production was also attributed to the release of large amounts of soluble carbohydrates and proteins with enzymatic pretreated SM and AW. The bacterial community analysis revealed that the hydrolytic bacteria Romboutsia and Clostridium_sensu_stricto_1 were enriched after enzyme pretreatment, and Lactobacillus was the dominant bacteria for LA production. This study provides an eco-friendly technology to enhance hydrolysis by enzymatic pretreatment and improve LA production during anaerobic fermentation.

Enhancing the Quality of Low-Alcohol Navel Orange Wine through Simultaneous Co-Fermentation Using Saccharomyces cerevisiae SC-125, Angel Yeast SY, and Lactiplantibacillus plantarum BC114.

To date, there has been limited research on the interactive effects of yeast and lactic acid bacteria (LAB) on the sensory qualities of navel orange wine. In this study, using Jintang navel orange juice as the raw material, multi-microbial fermentation was conducted with Saccharomyces cerevisiae SC-125 and Angel yeast SY, as well as Lactiplantibacillus plantarum BC114. Single yeast and co-fermentation with Lactiplantibacillus plantarum were used as the control groups. The research aimed to investigate the physicochemical parameters of navel orange wine during fermentation. Additionally, headspace solid-phase microextraction gas chromatography-mass spectrometry (HP-SPME-GC-MS) was employed to determine and analyze the types and levels of flavor compounds in the navel orange wines produced through the different fermentation methods. The co-fermentation using the three strains significantly enhanced both the quantity and variety of volatile compounds in the navel orange wine, concomitant with heightened total phenol and flavonoid levels. Furthermore, a notable improvement was observed in the free radical scavenging activity. A sensory evaluation was carried out to analyze the differences among the various navel orange wines, shedding light on the impact of different wine yeasts and co-fermentation with LAB on the quality of navel orange wines.

Identification of traits to improve co-assimilation of glucose and xylose by adaptive evolution of Spathaspora passalidarum and Scheffersomyces stipitis yeasts.

Lignocellulosic biomass is a renewable raw material for producing several high-value-added chemicals and fuels. In general, xylose and glucose are the major sugars in biomass hydrolysates, and their efficient utilization by microorganisms is critical for an economical production process. Yeasts capable of co-consuming mixed sugars might lead to higher yields and productivities in industrial fermentation processes. Herein, we performed adaptive evolution assays with two xylose-fermenting yeasts, Spathaspora passalidarum and Scheffersomyces stipitis, to obtain derived clones with improved capabilities of glucose and xylose co-consumption. Adapted strains were obtained after successive growth selection using xylose and the non-metabolized glucose analog 2-deoxy-D-glucose as a selective pressure. The co-fermentation capacity of evolved and parental strains was evaluated on xylose-glucose mixtures. Our results revealed an improved co-assimilation capability by the evolved strains; however, xylose and glucose consumption were observed at slower rates than the parental yeasts. Genome resequencing of the evolved strains revealed genes affected by non-synonymous variants that might be involved with the co-consumption phenotype, including the HXT2.4 gene that encodes a putative glucose transporter in Sp. passalidarum. Expression of this mutant HXT2.4 in Saccharomyces cerevisiae improved the cells' co-assimilation of glucose and xylose. Therefore, our results demonstrated the successful improvement of co-fermentation through evolutionary engineering and the identification of potential targets for further genetic engineering of different yeast strains. KEY POINTS: • Laboratory evolution assay was used to obtain improved sugar co-consumption of non-Saccharomyces strains. • Evolved Sp. passalidarum and Sc. stipitis were able to more efficiently co-ferment glucose and xylose. • A mutant Hxt2.4 permease, which co-transports xylose and glucose, was identified.

Waste cooking oil used as carbon source for microbial lipid production: Promoter or inhibitor.

In this study, waste cooking oil (WCO) co-fermentation with food waste by variable pH strategy was developed for microbial lipid production. Results showed that when WCO substitution rate within the range of 1.56-4.68% (corresponding to the WCO content in food waste), lipid production from Rhodosporidium toruloides 2.1389 could be increased by 7.2 g/kg food waste because of the better synergistic effect. Mechanism analysis revealed that the fatty acid salt produced from WCO under alkaline condition, as a surface active agent, could improve lipid production, but excessive WCO (29.2 g/L) would inhibit the lipid production due to its hindrance to the oxygen. The lipid composition analysis found that the produced lipid could be used as raw material for biodiesel production. It was estimated that 15.0 million tonnes of biodiesel could be produced from global food waste yearly by adopting the proposed WCO co-fermentation with variable pH strategy, together with reduction of about 0.31 million tonnes of CO2 equivalents and 1435 tonnes of SO2. It is expected that this study may lead to the paradigm shift in future biodiesel production from food waste.

Enhanced degradation of glucocorticoids, a potential COVID-19 remedy, by co-fermentation of waste activated sludge and animal manure: The role of manure type and degradation mechanism.

Waste activated sludge (WAS) and animal manure are two significant reservoirs of glucocorticoids (GCs) in the environment. However, GC degradation during anaerobic digestion (AD) of WAS or animal manure has rarely been investigated. In this study, co-fermentation of WAS and animal manure was conducted to investigate the performance of AD in controlling GC dissemination. Effects of manure type on GC degradation and sludge acidification were investigated. The results showed that co-fermentation of WAS and chicken manure (CM) significantly enhanced the degradation of hydrocortisone (HC) to 99%, betamethasone (BT) to 99%, fluocinolone acetonide (FA) to 98%, and clobetasol propionate (CP) to 82% in 5 days with a mixing ratio of 1:1 (g TS sludge/g dw manure) at 55 °C and initial pH of 7. Simultaneously, sludge reduction was increased by 30% and value-added volatile fatty acid (VFA) production was improved by 40%. Even a high GC content of biomass (3.6 mg/g TS) did not impact both sludge hydrolysis and acidification. The amendment of WAS with CM increased soluble organic carbon, Ca2+, and relative abundance of anaerobes (Eubacterium) associated with organic compound degradation. Furthermore, 44 transformation products of HC, BT, FA, and CP with lower lipophilicity and toxicity were identified, indicating possible degradation pathways including hydroxylation, ketonization, ring cleavage, defluorination, hydrogenation, methylation, and de-esterification. Overall, this study provides a practical way to control GC pollution and simultaneously promote waste reduction and VFA production. Animal manure type as an overlooked factor for influencing co-fermentation performance and pollutant degradation was also highlighted.

Sourdough yeast-bacteria interactions can change ferulic acid metabolism during fermentation.

The metabolism of ferulic acid (FA) was studied during fermentation with different species and strains of lactic acid bacteria (LAB) and yeasts, in synthetic sourdough medium. Yeast strains of Kazachstania humilis, Kazachstania bulderi, and Saccharomyces cerevisiae, as well as lactic acid bacteria strains of Fructilactobacillus sanfranciscensis, Lactiplantibacillus plantarum, Lactiplantibacillus xiangfangensis, Levilactobacillus hammesii, Latilactobacillus curvatus and Latilactobacillus sakei were selected from French natural sourdoughs. Fermentation in presence or absence of FA was carried out in LAB and yeasts monocultures, as well as in LAB/yeast co-cultures. Our results indicated that FA was mainly metabolized into 4-vinylguaiacol (4-VG) by S. cerevisiae strains, and into dihydroferulic acid (DHFA) and 4-VG in the case of LAB. Interactions of LAB and yeasts led to the modification of FA metabolism, with a major formation of DHFA, even by the strains that do not produce it in monoculture. Interestingly, FA was almost completely consumed by the F. sanfranciscensis bFs17 and K. humilis yKh17 pair and converted into DHFA in 89.5 ± 19.6% yield, while neither bFs17, nor yKh17 strains assimilated FA in monoculture.

Use of Hanseniaspora guilliermondii and Hanseniaspora opuntiae to enhance the aromatic profile of beer in mixed-culture fermentation with Saccharomyces cerevisiae.

Beer production is predominantly carried out by Saccharomyces species, such as S. cerevisiae and S. pastorianus. However, the introduction of non-Saccharomyces yeasts in the brewing process is now seen as a promising strategy to improve and differentiate the organoleptic profile of beer. In this study, 17 non-Saccharomyces strains of 12 distinct species were isolated and submitted to a preliminary sensory evaluation to determine their potential for beer bioflavouring. Hanseniaspora guilliermondii IST315 and H. opuntiae IST408 aroma profiles presented the highest acceptability and were described as having 'fruity' and 'toffee' notes, respectively. Their presence in mixed-culture fermentations with S. cerevisiae US-05 did not influence attenuation and ethanol concentration of beer but had a significant impact in its volatile composition. Notably, while both strains reduced the total amount of ethyl esters, H. guilliermondii IST315 greatly increased the concentration of acetate esters, especially when sequentially inoculated, leading to an 8.2-fold increase in phenylethyl acetate ('rose', 'honey' aroma) in the final beverage. These findings highlight the importance of non-Saccharomyces yeasts in shaping the aroma profile of beer and suggest a role for Hanseniaspora spp. in improving it.

Ecology of yeasts associated with kernels of several durum wheat genotypes and their role in co-culture with Saccharomyces cerevisiae during dough leavening.

This work was performed to investigate on the yeast ecology of durum wheat to evaluate the interaction between kernel yeasts and the commercial baker's yeast Saccharomyces cerevisiae during dough leavening. Yeast populations were studied in 39 genotypes of durum wheat cultivated in Sicily. The highest level of kernel yeasts was 2.9 Log CFU/g. A total of 413 isolates was collected and subjected to phenotypic and genotypic characterization. Twenty-three yeast species belonging to 11 genera have been identified. Filobasidium oeirense, Sporobolomyces roseus and Aureobasidium pullulans were the species most commonly found in durum wheat kernels. Doughs were co-inoculated with yeasts isolated from wheat kernels and commercial Saccharomyces cerevisiae, in order to evaluate the interactions between yeasts and the leavening performance. Yeast populations of all doughs have been monitored as well as dough volume increase and weight loss (as CO2) measured after 2 h of fermentation. The doughs whose final volume was higher than control dough (inoculated exclusively with S. cerevisiae) were those inoculated with Naganishia albida, Vishniacozyma dimennae (118 mL each), and Candida parapsilosis (102 mL). The weight losses were variable, depending on the co-culture used with S. cerevisiae and the values were in the range of 0.08-1.00 g CO2/100 g. The kernel yeasts species C. parapsilosis, N. albida, P. terrestris, R. mucilaginosa and V. dimennae deserves future attention to be co-inoculated with the commercial starter S. cerevisiae in order to improve the sensory characteristics of bread.

Co-fermentation process strongly affect the nutritional, texture, syneresis, fatty acids and aromatic compounds of dromedary UF-yogurt.

This work intended to compare dromedary yogurt's characteristics obtained by a co-fermentation process with plant (carob powder) or autochthonous bacteria (Enterococcus faecium and Streptococcus macedonicus). For this reason, the ultrafiltration process (UF) is applied to increase the rate of total solids in dromedary milk within the margin needed to prepare a yogurt. Carob powder or autochthonous bacteria were incorporated at the level of 2% in UF milk. Then mixtures were fermented with the strains Lactobacillus bulgaricus and Streptococcus thermophiles, and the obtained products are named CFC (yogurt with carob), CFS (yogurt with autochthonous strains) and control (yogurt with only L. bulgaricus and S. thermophilus) respectively. All along of 3 weeks at cold, CFC and CFS maintained Streptococcus at appropriate levels (>8 log CFU/g). Moreover, CFC showed the lowest syneresis, highest cohesiveness and springiness values, and oleic acid (C18:1n9; 26.315%). However, CFS yogurt resulted in higher volatile compound formation than CFC and control, where isobornyl propionate was the major one.

Ethanol Metabolism Dynamics in Clostridium ljungdahlii Grown on Carbon Monoxide.

Bioethanol production from syngas using acetogenic bacteria has attracted considerable attention in recent years. However, low ethanol yield is the biggest challenge that prevents the commercialization of syngas fermentation into biofuels using microbial catalysts. The present study demonstrated that ethanol metabolism plays an important role in recycling NADH/NAD+ during autotrophic growth. Deletion of bifunctional aldehyde/alcohol dehydrogenase (adhE) genes leads to significant growth deficiencies in gas fermentation. Using specific fermentation technology in which the gas pressure and pH were constantly controlled at 0.1 MPa and 6.0, respectively, we revealed that ethanol was formed during the exponential phase, closely accompanied by biomass production. Then, ethanol was oxidized to acetate via the aldehyde ferredoxin oxidoreductase pathway in Clostridium ljungdahlii A metabolic experiment using 13C-labeled ethanol and acetate, redox balance analysis, and comparative transcriptomic analysis demonstrated that ethanol production and reuse shared the metabolic pathway but occurred at different growth phases.IMPORTANCE Ethanol production from carbon monoxide (CO) as a carbon and energy source by Clostridium ljungdahlii and "Clostridium autoethanogenum" is currently being commercialized. During gas fermentation, ethanol synthesis is NADH-dependent. However, ethanol oxidation and its regulatory mechanism remain incompletely understood. Energy metabolism analysis demonstrated that reduced ferredoxin is the sole source of NADH formation by the Rnf-ATPase system, which provides ATP for cell growth during CO fermentation. Therefore, ethanol production is tightly linked to biomass production (ATP production). Clarification of the mechanism of ethanol oxidation and biosynthesis can provide an important reference for generating high-ethanol-yield strains of C. ljungdahlii in the future.

In vitro antioxidant and angiotensin-converting enzyme inhibitory activity of fermented milk with different culture combinations.

This study investigated the effects of Lactobacillus plantarum (Lp) and Bifidobacterium animalis ssp. lactis (Ba) in co-cultures with Streptococcus thermophilus (St) on changes in the acidification profile, proteolytic activity, peptide production, in vitro antioxidant activity, and angiotensin-converting enzyme (ACE) inhibitory properties of fermented milks during 21 d of storage at 4°C. The pH values and proteolysis in all batches showed a gradual decrease and increase during storage, respectively. The ACE-inhibitory activity and total antioxidant capacity of all co-fermented milk samples followed a similar pattern, with maximum values on d 6 of storage. The St starter, in conjunction with Ba or Lp or both, enhanced proteolysis, peptide generation, and ACE-inhibitory and antioxidant activity, but decreased pH values compared with St alone. The St-Ba-Lp samples showed higher DPPH• (1,1-diphenyl-2-picrylhydrazyl) radical scavenging activity, hydroxyl radical scavenging activity, and total antioxidant capacity, but similar superoxide anion scavenging activity compared to St-Ba or St-Lp samples. The St-Ba samples showed higher DPPH• radical scavenging activity but lower hydroxyl radical scavenging activity than St-Lp samples. In the ACE-inhibitory assays, the St-Lp samples exhibited relatively low activity among the co-fermented milks, digested or not. The presence of Ba and Lp in fermentation together did not affect ACE-inhibitory activity in undigested fermented milks compared with the presence of Ba alone, and St-Ba-Lp fermented milks demonstrated an increase in ACE-inhibitory activity after simulated gastrointestinal digestion in storage. Pepsin digestion largely improved ACE-inhibitory activity, except in St-Lp samples, in which the activity was reduced. Further hydrolysis by trypsin reduced final activity in digestion. This study suggests that co-cultured fermentation with probiotics improves in vitro antioxidant and ACE inhibition activity in fermented milks, and this effect is partly due to the higher proteolytic activity of probiotics.

Rhizopus oligosporus and Lactobacillus plantarum Co-Fermentation as a Tool for Increasing the Antioxidant Potential of Grass Pea and Flaxseed Oil-Cake Tempe.

Tempe-type fermentation originating from Indonesia can enhance the antioxidant activity of plant material. However, this biological potential depends on substrates and applied microorganisms. This study aimed to determine whether co-fermentation with Rhizopus oligosporus and Lactobacillus plantarum improved antioxidant activity of tempe obtained from grass pea seeds with flaxseed oil-cake addition (up to 30%). For this purpose, substances reacting with Folin-Ciocalteu reagent and free radicals scavenging potential were measured in water-soluble fractions and dialysates from simulated in vitro digestion. Additionally, the water-soluble phenolic profile was estimated. The higher level of water-extractable compounds with antioxidant activity was determined in co-fermentation products than in fungal fermentation products. Moreover, the fermentation process with the use of L. plantarum contributed to a greater accumulation of some phenolic acids (gallic acid, protocatechuic acid) in tempe without having a negative effect on the levels of other phenolic compounds determined in fungal fermented tempe. During in vitro digestion simulating the human digestive tract, more antioxidant compounds were released from products obtained after co-fermentation than fungal fermentation. An addition of 20% flaxseed oil-cake and the application of bacterial-fungal co-fermentation, can be considered as an alternative tool to enhance the antioxidant parameters of grass pea tempe.

Combined indigenous yeast strains produced local wine from over ripen Cabernet Sauvignon grape in Xinjiang.

Cabernet Sauvignon grape produced in Xinjiang (China) is often overripe, with unusually high sugar content, which impedes utilization. We aimed to establish the optimal combination of indigenous yeast strains to produce a new sweet wine from the overripe grape. Five yeast strains with pronounced enological characteristics were selected from 88 indigenous yeast isolates. Using a series of co-fermentation experiments with different inoculated strategies, we achieved optimal co-fermentation with a combination of strains SC19 and NS68, later identified as Saccharomyces cerevisiae and Pichia kudriavzevii, respectively, simultaneously inoculated in a 1:1 ratio at the early stage of fermentation. The combination was characterized by vigorous fermentation with high resistance to 457.13 g/L sugar and high alcohol yield (16.01% vol). The sweet wine contained 17 aromatic compounds with odor activity value (OAV) ≥ 1 and pronounced sweet fruit, floral, herbaceous, and caramel odors. The co-fermentation has a good potential for utilization of overripe Cabernet Sauvignon grape.

Overview of key operation factors and strategies for improving fermentative volatile fatty acid production and product regulation from sewage sludge.

In recent years, volatile fatty acid (VFA) production through anaerobic fermentation of sewage sludge, instead of methane production, has been regarded as a high-value and promising roadmap for sludge stabilization and resource recovery. This review first presents the effects of some essential factors that influence VFA production and composition. In the second part, we present an extensive analysis of conventional pretreatment and co-fermentation strategies ultimately addressed to improving VFA production and composition. Also, the effectiveness of these approaches is summarized in terms of sludge degradation, hydrolysis rate, and VFA production and composition. According to published studies, it is concluded that some pretreatments such as alkaline and thermal pretreatment are the most effective ways to enhance VFA production from sewage sludge. The possible reasons for the improvement of VFA production by different methods are also discussed. Finally, this review also highlights several current technical challenges and opportunities in VFA production with spectrum control, and further related research is proposed.

Efficient, D-glucose insensitive, growth on D-xylose by an evolutionary engineered Saccharomyces cerevisiae strain.

Optimizing D-xylose consumption in Saccharomyces cerevisiae is essential for cost-efficient cellulosic bioethanol production. An evolutionary engineering approach was used to elevate D-xylose consumption in a xylose-fermenting S. cerevisiae strain carrying the D-xylose-specific N367I mutation in the endogenous chimeric Hxt36 hexose transporter. This strain carries a quadruple hexokinase deletion that prevents glucose utilization, and allows for selection of improved growth rates on D-xylose in the presence of high D-glucose concentrations. Evolutionary engineering resulted in D-glucose-insensitive growth and consumption of D-xylose, which could be attributed to glucose insensitive D-xylose uptake via a novel chimeric Hxt37 N367I transporter that emerged from a fusion of the HXT36 and HXT7 genes, and a down regulation of a set of Hxt transporters that mediate glucose sensitive xylose transport. RNA sequencing revealed the downregulation of HXT1 and HXT2 which, together with the deletion of HXT7, resulted in a 21% reduction of the expression of all plasma membrane transporters genes. Morphological analysis showed an increased cell size and corresponding increased cell surface area of the evolved strain, which could be attributed to genome duplication. Mixed strain fermentation of the D-xylose-consuming strain DS71054-evo6 with the D-glucose consuming CEN.PK113-7D strain resulted in decreased residual sugar concentrations and improved ethanol production yields compared to a strain which sequentially consumes D-glucose and D-xylose.