Reduced production of Ethyl Carbamate in wine by regulating the accumulation of arginine in Saccharomyces cerevisiae.

Ethyl carbamate (EC), a multisite carcinogenic compound, is naturally produced from urea and ethanol in alcoholic beverages. In order to reduce the content of EC in wine, the accumulation of arginine in Saccharomyces cerevisiae was regulated by genetic modifying genes involved in arginine transport and synthesis pathways to reduce the production of urea. Knockout of genes encoding arginine permease (Can1p) and amino acid permease (Gap1p) on the cell membrane as well as argininosuccinate synthase (Arg1) respectively resulted in a maximum reduction of 66.88% (9.40 µg/L) in EC, while overexpressing the gene encoding amino acid transporter (Vba2) reduced EC by 52.94% (24.13 µg/L). Simultaneously overexpressing Vba2 and deleting Arg1 showed the lowest EC production with a decrease of 68% (7.72 µg/L). The yield of total higher alcohols of the mutants all decreased compared with that of the original strain. Comprehensive consideration of flavor compound contents and sensory evaluation results indicated that mutant YG21 obtained by deleting two allele coding Gap1p performed best in must fermentation of Cabernet Sauvignon with the EC content low to 9.40 µg/L and the contents of total higher alcohols and esters of 245.61 mg/L and 41.71 mg/L respectively. This study has provided an effective strategy for reducing the EC in wine.

Formation and hazard of ethyl carbamate and construction of genetically engineered Saccharomyces cerevisiae strains in Huangjiu (Chinese grain wine).

Huangjiu, a well-known conventional fermented Chinese grain wine, is widely consumed in Asia for its distinct flavor. Trace amounts of ethyl carbamate (EC) may be generated during the fermentation or storage process. The International Agency for Research on Cancer elevated EC to a Class 2A carcinogen, so it is necessary to regulate EC content in Huangjiu. The risk of intake of dietary EC is mainly assessed through the margin of exposure (MOE) recommended by the European Food Safety Authority, with a smaller MOE indicating a higher risk. Interventions are necessary to reduce EC formation. As urea, one of the main precursors of EC formation in Huangjiu, is primarily produced by Saccharomyces cerevisiae through the catabolism of arginine, the construction of dominant engineered fermentation strains is a favorable trend for the future production and application of Huangjiu. This review summarized the formation and carcinogenic mechanism of EC from the perspectives of precursor substances, metabolic pathways after ingestion, and risk assessment. The methods of constructing dominant S. cerevisiae strains in Huangjiu by genetic engineering technology were reviewed, which provided an important theoretical basis for reducing EC content and strengthening practical control of Huangjiu safety, and the future research direction was prospected.

Comparative analysis of hippocampal extracellular space uncovers widely altered peptidome upon epileptic seizure in urethane-anaesthetized rats.

BACKGROUND: The brain extracellular fluid (ECF), composed of secreted neurotransmitters, metabolites, peptides, and proteins, may reflect brain processes. Analysis of brain ECF may provide new potential markers for synaptic activity or brain damage and reveal additional information on pathological alterations. Epileptic seizure induction is an acute and harsh intervention in brain functions, and it can activate extra- and intracellular proteases, which implies an altered brain secretome. Thus, we applied a 4-aminopyridine (4-AP) epilepsy model to study the hippocampal ECF peptidome alterations upon treatment in rats. METHODS: We performed in vivo microdialysis in the hippocampus for 3-3 h of control and 4-AP treatment phase in parallel with electrophysiology measurement. Then, we analyzed the microdialysate peptidome of control and treated samples from the same subject by liquid chromatography-coupled tandem mass spectrometry. We analyzed electrophysiological and peptidomic alterations upon epileptic seizure induction by two-tailed, paired t-test. RESULTS: We detected 2540 peptides in microdialysate samples by mass spectrometry analysis; and 866 peptides-derived from 229 proteins-were found in more than half of the samples. In addition, the abundance of 322 peptides significantly altered upon epileptic seizure induction. Several proteins of significantly altered peptides are neuropeptides (Chgb) or have synapse- or brain-related functions such as the regulation of synaptic vesicle cycle (Atp6v1a, Napa), astrocyte morphology (Vim), and glutamate homeostasis (Slc3a2). CONCLUSIONS: We have detected several consequences of epileptic seizures at the peptidomic level, as altered peptide abundances of proteins that regulate epilepsy-related cellular processes. Thus, our results indicate that analyzing brain ECF by in vivo microdialysis and omics techniques is useful for monitoring brain processes, and it can be an alternative method in the discovery and analysis of CNS disease markers besides peripheral fluid analysis.

TNF-α-dependent lung inflammation upregulates PD-L1 in monocyte-derived macrophages to contribute to lung tumorigenesis.

Chronic inflammation, which is dominated by macrophage-involved inflammatory responses, is an instigator of cancer initiation. Macrophages are the most abundant immune cells in healthy lungs, and associated with lung tumor development and promotion. PD-L1 is a negative molecule in macrophages and correlated with an immunosuppressive function in tumor environment. Macrophages expressing PD-L1, rather than tumor cells, exhibits a critical role in tumor growth and progression. However, whether and how PD-L1 in macrophages contributes to inflammation-induced lung tumorigenesis requires further elucidation. Here, we found that higher expression of PD-L1 in CD11b+ CD206+ macrophages was positively correlated with tumor progression and PD-1+ CD8+ T cells population in human adenocarcinoma patients. In the urethane-induced inflammation-driven lung adenocarcinoma (IDLA) mouse model, the infiltration of circulating CD11bhigh F4/80+ monocyte-derived macrophages (MoMs) was increased in pro-tumor inflamed lung tissues and lung adenocarcinoma. PD-L1 was mainly upregulated in MoMs associated with enhanced T cells exhaustion in lung tissues. Anti-PD-L1 treatment can reduce T cells exhaustion at pro-tumor inflammatory stage, and then inhibit tumorigenesis in IDLA. The pro-tumor lung inflammation depended on TNF-α to upregulate PD-L1 and CSN6 expression in MoMs, and induced cytokines production by alveolar type-II cells (AT-II). Furthermore, inflammatory AT-II cells could secret TNF-α to upregulate PD-L1 expression in bone-marrow driven macrophages (BM-M0). Inhibition of CSN6 decreased PD-L1 expression in TNF-α-activated macrophage in vitro, suggesting a critical role of CSN6 in PD-L1 upregulation. Thus, pro-tumor inflammation can depend on TNF-α to upregulate PD-L1 in recruited MoMs, which may be essential for lung tumorigenesis.

Saccharomyces cerevisiae strains with low-yield higher alcohols and high-yield acetate esters improve the quality, drinking comfort and safety of huangjiu.

Higher alcohols (HAs) and acetate esters (AEs) produced by yeasts are two important volatile flavor substances in fermented alcoholic beverages (FABs). To improve the FABs overall quality, lab-scale huangjiu brewing and systematic evaluation were performed using 171 Saccharomyces cerevisiae strains. Finally, two S. cerevisiae strains that produced lower HAs and higher AEs were obtained and named jiangnan1# and jiangnan3#, respectively. The results of production-scale huangjiu fermentation indicated that HAs produced by jiangnan1# sample decreased by 24.99 %, and AEs produced by jiangnan1# increased by 36.35 %. Sensory evaluation showed that the acidic taste, honey aroma attribute intensity were higher in 85# huagnjiu, and the fruity aroma attribute intensity was higher in jiangnan1# huangjiu (P < 0.01). Moreover, urea and ethyl carbamate produced by jiangnan1# strain were degraded by 13.89 % and 45.51 % compared with those of the control strain 85#, indicating the positive effects of jiangnan1# strain on health and safety. Thus, the obtained S. cerevisiae strains in this study can better enhance the flavor and improve the drinking safety and comfort of huangjiu.

Inhibitory effects of vibegron, a ß3-adrenoceptor agonist, on the myogenic contractile and mechanosensitive afferent activities in an obstructed rat bladder.

To determine the role of ß3-adrenoceptor agonists on bladder sensory facilitation related to bladder myogenic contractile activities in bladder hyperactivity, we investigated the effects of vibegron, a ß3-adrenoceptor agonist, on the bladder and sensory function by evaluating cystometry and mechanosensitive single-unit afferent activities (SAAs), respectively, in a male rat model of bladder outlet obstruction (BOO). BOO was created by partial ligation of the urethra. Ten days after the surgical procedure, cystometric and SAA measurements were taken under two distinct conditions: a conscious-restrained condition, in which the bladder was constantly filled with saline, and a urethane-anesthetized condition involving an isovolumetric process with saline. For each measurement, vibegron (3 mg/kg) or its vehicle was administered intravenously after the data were reproducibly stable. In addition, the expression of ß3-adrenoceptor and substance P (SP), a sensory neuropeptide, in the bladder was further evaluated following immunohistochemical procedures. Number of non-voiding contractions (NVCs) in cystometry was decreased after vibegron-administration, which was a significant change from vehicle group. Number of microcontractions and SAAs of Aδ- and C-fibers were significantly decreased by vibegron-administration. Furthermore, ß3-adrenocepor and SP were co-expressed in the suburothelium layer of the bladder. These findings indicated that vibegron showed inhibitory effects on NVCs and microcontractions of the bladder, and SAAs of the Aδ- and C-fibers in BOO rats. The study suggested that vibegron can partly inhibit the mechanosensitive afferent transduction via Aδ- and C-fibers by suppressing bladder myogenic contractile activities in the rat bladder hyperactivity associated with BOO.

Sequence and Structure-Guided Engineering of Urethanase from Agrobacterium tumefaciens d3 for Improved Catalytic Activity.

The amidase from Agrobacterium tumefaciens d3 (AmdA) degrades the carcinogenic ethyl carbamate (EC) in alcoholic beverages. However, its limited catalytic activity hinders practical applications. Here, multiple sequence alignment was first used to predict single variants with improved activity. Afterward, AlphaFold 2 was applied to predict the three-dimensional structure of AmdA and 21 amino acids near the catalytic triad were randomized by saturation mutagenesis. Each of the mutation libraries was then screened, and the improved single variants were combined to obtain the best double variant I97L/G195A that showed a 3.1-fold increase in the urethanase activity and a 1.5-fold increase in ethanol tolerance. MD simulations revealed that the mutations shortened the distance between catalytic residues and the substrate and enhanced the occurrence of a critical hydrogen bond in the catalytic pocket. This study displayed a useful strategy to engineer an amidase for the improvement of urethanase activity, and the variant obtained provided a good candidate for applications in the food industry.

Features and application potential of microbial urethanases.

Urethanase (EC 3.5.1.75) can reduce ethyl carbamate (EC), a group 2A carcinogen found in foods and liquor. However, it is not yet commercially available. Urethanase has been detected as an intracellular enzyme from yeast, filamentous fungi, and bacteria. Based on the most recent progress in the sequence analysis of this enzyme, it was observed that amidase-type enzyme can degrade EC. All five enzymes had highly conserved sequences of amidase signature family, and their molecular masses were in the range of 52-62 kDa. The enzymes of Candida parapsilosis and Aspergillus oryzae formed a homotetramer, and that of Rhodococcus equi strain TB-60 existed as a monomer. Most urethanases exhibited amidase activity, and those of C. parapsilosis and A. oryzae also demonstrated high activity against acrylamide, which is a group 2A carcinogen. It was recently reported that urease and esterase also exhibited urethanase activity. Although research on the enzymatic degradation of EC has been very limited, recently some sequences of EC-degrading enzyme have been elucidated, and it is anticipated that new enzymes would be developed and applied into practical use. KEY POINTS: • Recently, some urethanase sequences have been elucidated • The amino acid residues that formed the catalytic triad were conserved • Urethanase shows amidase activity and can also degrade acrylamide.

Correlation between the microbial community and ethyl carbamate generated during Huzhou rice wine fermentation.

Ethyl carbamate (EC) is a potential carcinogen that is mainly produced by the spontaneous reaction between urea and ethanol during rice wine brewing. Huzhou rice wine (HZRW) is a traditional Chinese rice wine, but the correlation between its urea content and the microbial communities present during the fermentation process has not yet been evaluated. In this study, high-throughput sequencing technology was used to monitor the microbial community composition of HZRW in the different fermentation stages. The correlations between the microbial community and the physical and chemical properties and EC, urea and arginine contents were evaluated using the redundancy analysis (RDA) method. The metabolic profiles of key genes in the arginine and urea metabolic pathways were obtained via phylogenetic investigation of the communities by reconstruction of unobserved states (PICRUSt). The results showed that the fungal genera Saccharomyces, Issatchenkia, Torulaspora and Rhizopus were dominant during the fermentation of HZRW. Weissella and Acinetobacter were the dominant bacterial genera in the early stage, while Weissella, Staphylococcus, Leuconostoc and Streptophyta were the dominant bacterial genera in the late stage. Urea and arginine were positively correlated with Saccharomyces, Lactobacillus and Staphylococcus. In addition, the dominant genera of both fungi and bacteria were involved in the metabolism of arginine and urea. Finally, the relationships between the dominant microorganisms and key genes of the arginine and urea metabolic pathways were established. The obtained results are helpful in better understanding the mechanisms of metabolism of arginine and urea during rice wine fermentation and therefore improving the safety profile of rice wine.

Identification and expression of bifunctional acid urea-degrading enzyme/urethanase from Enterobacter sp. R-SYB082 and its application in degradation of ethyl carbamate in Chinese rice wine (Huangjiu).

BACKGROUND: Ethyl carbamate (EC) is a potential carcinogen existing in fermented foods such as Chinese rice wine (Huangjiu). Since urea is an important precursor of EC, the degradation of urea could be an effective way to reduce EC in foods. RESULTS: In this study, an Enterobacter sp. R-SYB082 with acid urea degradation characteristics was obtained through microbial screening. Further research isolated a new acid urea-degrading enzyme from R-SYB082 strain - ureidoglycolate amidohydrolase (UAH) - which could degrade EC directly. The cloning and expression of UAH in Escherichia coli BL21 (DE3) suggested that the activity of urea-degrading enzyme reached 3560 U L-1 , while urethanase activity reached 2883 U L-1 in the optimal fermentation condition. The enzyme had the dual ability of degrading substrate urea and product EC. The removal rate of EC in Chinese rice wine could reach 90.7%. CONCLUSION: This study provided a new method for the integrated control of EC in Chinese rice wine and other fermented foods. © 2022 Society of Chemical Industry.

The experimental study of regeneration of annulus fibrosus using decellularized annulus fibrosus matrix/poly(ether carbonate urethane)urea-blended fibrous scaffolds with varying elastic moduli.

Although tissue engineering has attracted increasing attention for the treatment of degenerative intervertebral disc disease, the biochemical properties, structural organization, and mechanical characteristics of annulus fibrosus tissue have restricted progress. Differentiation of annulus fibrosus-derived stem cells (AFSCs) can be regulated by the elasticity of substrates such as poly(ether carbonate urethane)urea (PECUU). Decellularized annulus fibrosus matrix (DAFM) has good biocompatibility and biodegradability, making it suitable for cell adhesion, proliferation, and differentiation. In this study, we used a coaxial electrospinning method to synthesize DAFM/PECUU-blended fibrous scaffolds with elasticities approximating that of native inner and outer annulus fibrosus tissue. AFSCs cultured on DAFM/PECUU-blended fibrous scaffolds exhibited increased collagen type I gene expression with increasing elasticity of the scaffold material; notably, collagen type II and aggrecan gene expression exhibited the opposite trend. Regarding extracellular matrix secretion, collagen type I content gradually increased with substrate elasticity, while collagen type II and aggrecan contents decreased. In vivo evaluations employing magnetic resonance imaging, hematoxylin and eosin staining, and immunohistochemistry indicated that DAFM/PECUU-blended fibrous scaffolds could effectively repair defects of annulus fibrosus tissue. Our findings provide a theoretical and practical basis for the development of bionic annulus fibrosus tissue that closely mimics the biological properties, mechanical function, and matrix composition of native tissue.

Effects of the pre-fermentative addition of chitosan on the nitrogenous fraction and the secondary fermentation products of SO2 -free red wines.

BACKGROUND: Different red winemaking were carried out to evaluate the effects of the prefermentative addition of chitosan, as an alternative to the use of SO2 , on the secondary products of alcoholic fermentation, yeast available nitrogen (YAN), biogenic amines and ethyl carbamate. RESULTS: The wines made with chitosan presented higher total acidity and higher content of tartaric and succinic acids than those made only with SO2 . The use of chitosan in winemaking resulted in wines with higher glycerol and diacetyl content without increasing the concentration of ethanol, acetic acid, acetaldehyde or butanediol. YAN was lower in wines made with chitosan, which may mean an advantage for the microbial stability of the wines. Furthermore, the use of chitosan at the beginning of alcoholic fermentation did not increase the concentration of biogenic amines or the formation of ethyl carbamate in SO2 -free red wines. CONCLUSION: The total or partial substitution of SO2 for chitosan at the beginning of the alcoholic fermentation gives rise to quality red wines without negatively affecting their nitrogen fraction or their very important secondary fermentation products such as acetic acid or acetaldehyde. © 2020 Society of Chemical Industry.

Identification and characterization of a polyurethanase with lipase activity from Serratia liquefaciens isolated from cold raw cow's milk.

Lipases are associated with food spoilage and are also used in various biotechnological applications. In this study, we sought to purify, identify, and characterize a lipase from S. liquefaciens isolated from cold raw cow's milk. The lipase partially purified by ultrafiltration and gel filtration showed a specific activity of 2793 U/mg. By zymography, the enzyme presented approximately 65 kDa, and LC-MS/MS allowed the identification of a polyurethanase with a conserved domain of family I.3 lipase. The modeled and validated structure of polyurethanase was able to bind to different fatty acids and urethane by molecular docking. The polyurethanase showed optimum activity at pH 8.0 and 30 °C. In the presence of ions, activity was decreased, except for Ca2+, Mg2+, and Ba2+. Reducing agents did not alter the activity, while amino acid modifiers reduced enzyme activity. It is concluded that polyurethanase with lipase activity represents a potential enzyme for the deterioration of milk and dairy products, as well as a candidate for industrial applications.

UHPLC-QTOFMS-based metabolomic analysis of serum and urine in rats treated with musalais containing varying ethyl carbamate content.

The aim of this work is to investigate the effect of the ethyl carbamate (EC) content in musalais on the metabolism of rats. Electron beam irradiation was performed to decrease the content of EC in musalais, and Sprague Dawley rats were subjected to intragastric administration of musalais with varying EC content (high, medium, and low groups). Control rats were fed normally without any treatment. Serum and urine samples were analyzed using ultra-high-performance liquid chromatography quadrupole time-of-flight mass spectrometry. Principal component analysis and orthogonal projections to latent structures discriminant analysis (OPLS-DA) were performed to detect changes in the metabolite profile in the serum and urine in order to identify the differential metabolites and metabolic pathways. The results demonstrated clear differences in the serum and urine metabolic patterns between control and treatment groups. Ions in treatment groups with variable importance in the projection of >1 (selected from the OPLS-DA loading plots) and Ps < 0.05 (Student t test) compared to control group were identified as candidate metabolites. Analysis of the metabolic pathways relevant to the identified differential metabolites revealed that high EC content in musalais (10 mg/kg) mainly affected rats through valine, leucine, and isoleucine biosynthesis and nicotinate and nicotinamide metabolism, which were associated with energy metabolism. In addition, this work suggests that EC can induce oxidative stress via inhibition of glycine content.

[Improving applicability of urease from Bacillus amyloliquefaciens JP-21 by site-directed mutagenesis].

Ethyl carbamate (EC) is a carcinogen detected in fermented foods and alcohol beverages. Excessive intake of EC is possibly harmful to health. Enzymatic degradation is one of the most effective approaches for reducing EC in fermented foods. Urease catalyzes the hydrolysis of both EC and urea. This confers urease a good application prospect in reducing EC and its precursor urea in fermented foods. Currently, degradation of EC in alcohol beverages by urease is inefficient due to its low urethanase activity and poor affinity to EC. Urease from Bacillus amyloliquefaciens JP-21 was successfully expressed in Escherichia coli at the level of 3 292 U/L urease and 227.3 U/L urethanase. Two key residues M326 and M374 were characterized that might block the binding of enzyme to EC, through simulating docking the structure of catalytic subunit UreC of urease with EC. Three mutants (M374A, M374T and M326V) of urease with improved urethanase activity were obtained by performing point saturated mutagenesis approach. Using EC as the substrate, Km values of M374A, M374T and M326V were detected to be 101.8 mmol/L, 129.5 mmol/L and 121.7 mmol/L, respectively, which were decreased by 37.47%-50.82% compared with that of the wild type urease. These mutants can degrade more than 97% of urea in rice wine and mutant M374T shows the highest degradation of EC in rice wine. EC content in rice wine was reduced from 525 µg/L to 393 µg/L by using M374T, and the EC degradation rate of it is 0.97 folds higher than that of the wild type urease. The results are of great significance for engineering the catalytic properties of urease and improving its industrial properties, and lays a good foundation for developing strategies to reducing microbial metabolic ammonia (amine) hazards in fermented foods.

Chinese Yellow Rice Wine Processing with Reduced Ethyl Carbamate Formation by Deleting Transcriptional Regulator Dal80p in Saccharomyces cerevisiae.

Ethyl carbamate (EC) is a potential carcinogen that forms spontaneously during Chinese rice wine fermentation. The primary precursor for EC formation is urea, which originates from both external sources and arginine degradation. Urea degradation is suppressed by nitrogen catabolite repression (NCR) in Saccharomyces cerevisiae. The regulation of NCR is mediated by two positive regulators (Gln3p, Gat1p/Nil1p) and two negative regulators (Dal80p/Uga43p, Deh1p/Nil2p/GZF3p). DAL80 revealed higher transcriptional level when yeast cells were cultivated under nitrogen-limited conditions. In this study, when DAL80-deleted yeast cells were compared to wild-type BY4741 cells, less urea was accumulated, and genes involved in urea utilization were up-regulated. Furthermore, Chinese rice wine fermentation was conducted using dal80Δ cells; the concentrations of urea and EC were both reduced when compared to the BY4741 and traditional fermentation starter. The findings of this work indicated Dal80p is involved in EC formation possibly through regulating urea metabolism and may be used as the potential target for EC reduction.

Assessment of oral ciprofloxacin impaired gut barrier integrity on gut bacteria in mice.

Gut bacteria and gut barrier plays important roles in body homeostasis. Ciprofloxacin (CPFX) is widely used to treat bacterial infections. However, whether high dosage of CPFX has side effects on gut barrier integrity is still unclear. Our results indicated that the High CPFX treatment (1 mg/ml) caused weight loss, nervousness, anorexia, and increased apoptosis cells in gut, but less influence was observed in the Low CPFX group (0.2 mg/ml). Meanwhile, the High CPFX treatment impaired tight junction molecules Ocln/ZO-1 level and down-regulated antibacterial genes expression (reg3γ, pla2g2α and defb1). Further, the High CPFX treatment increased pro-inflammatory cytokine IL-1ß in intestinal tract, decreased IL-17A of duodenum but increased IL-17A of colon at day 37. In addition, the gut bacterial diversity and richness behaved significantly loss regarding CPFX treatment, especially in the High CPFX group during the experiment. Indole exhibited sharply decline in both Low and High CPFX groups at day 7, and the High CPFX mice needed longer time on restoring indole level. Meanwhile, CPFX treatment strongly decreased the concentrations of butyric acid and valeric acid at day 1. Correlation analysis indicated that the linked patterns between the key bacteria (families Bacteroidales_S247, Ruminococcaceae and Desulfovibrionaceae) and metabolites (indole and butyric acid) were disturbed via the CPFX treatment. In conclusion, the High CPFX treatment impaired the gut barrier with the evidence of reduced expression of tight junction proteins, increased apoptosis cells and inflammatory cells, decreased the bacterial diversity and composition, which suggesting a proper antibiotic-dosage use should be carefully considered in disease treatment.

New urethanase from the yeast Candida parapsilosis.

Urethanase (EC 3.5.1.75) is an effective enzyme for removing ethyl carbamate (EC) present in alcoholic beverages. However, urethanase is not well studied and has not yet been developed for practical use. In this study, we report a new urethanase (CPUTNase) from the yeast Candida parapsilosis. Because C. parapsilosis can assimilate EC as its sole nitrogen source, the enzyme was extracted from yeast cells and purified using ion-exchange chromatography. The CPUTNase was estimated as a homotetramer comprising four units of a 61.7 kDa protein. In a 20% ethanol solution, CPUTNase had 73% activity compared with a solution without ethanol. Residual activity after 18 h indicated that CPUTNase was stable in 0%-40% ethanol solutions. The optimum temperature of CPUTNase was 43°C. This enzyme showed urethanase activity at pH 5.5-10.0 and exhibited its highest activity at pH 10. The gene of CPUTNase was identified, and a recombinant enzyme was expressed in the yeast Saccharomyces cerevisiae. Characteristics of recombinant CPUTNase were identical to the native enzyme. The putative amino acid sequence indicated that CPUTNase was an amidase family protein. Further, substrate specificity supported this sequence analysis because CPUTNase showed higher activities toward amide compounds. These results suggest that amidase could be a candidate for urethanase. We discovered a new enzyme and investigated its enzymatic characteristics, sequence, and recombinant CPUTNase expression. These results contribute to a further understanding of urethanase.

Metabolic engineering of Saccharomyces cerevisiae using the CRISPR/Cas9 system to minimize ethyl carbamate accumulation during Chinese rice wine fermentation.

Ethyl carbamate (EC) is a potential carcinogen to humans that is mainly produced through the spontaneous reaction between urea and ethanol during Chinese rice wine brewing. We metabolically engineered a strain by over-expressing the DUR3 gene in a previously modified strain using an improved CRISPR/Cas9 system to further decrease the EC level. Homologous recombination of the DUR3 over-expression cassette was performed at the HO locus by individual transformation of the constructed plasmid CRISPR-DUR3-gBlock-HO, generating the engineered strain N85DUR1,2/DUR3-c. Consequently, the DUR3 expression level was significantly enhanced in the modified strain, resulting in increased utilization of urea. The brewing test showed that N85DUR1,2/DUR3-c reduced urea and EC concentrations by 92.0% and 58.5%, respectively, compared with those of the original N85 strain. Moreover, the engineered strain showed good genetic stability in reducing urea content during the repeated brewing experiments. Importantly, the genetic manipulation had a negligible effect on the growth and fermentation characteristics of the yeast strain. Therefore, the constructed strain is potentially suitable for application to reduce urea and EC contents during production of Chinese rice wine. KEY POINTS: • An efficient CRISPR vector was constructed and applied for DUR3 over-expression. • Multi-modification of urea cycle had synergistic effect on reducing EC level. • Fermentation performance of engineered strain was similar with the parental strain. • No residual heterologous genes were left in the genome after genetic manipulation. • An efficient CRISPR vector was constructed and applied for DUR3 over-expression. • Multi-modification of urea cycle had synergistic effect on reducing EC level. • Fermentation performance of engineered strain was similar with the parental strain. • No residual heterologous genes were left in the genome after genetic manipulation.

Application of bamboo leaves extract to Chinese yellow rice wine brewing for ethyl carbamate regulation and its mitigation mechanism.

Bamboo leaves extract (BLE) contains various effective ingredients, including phenolic compounds. In this study, the effect of BLE on ethyl carbamate (EC) formation was investigated in Chinese yellow rice wine brewing with three different fermentation starters (Saccharomyces cerevisiae, Saccharomyces cerevisiae and Lactobacillus brevis, and Chinese yeast). As a result, BLE showed significant inhibition effect on EC in multi-microbial fermented rice wine, by preventing the reactions between urea/citrulline and ethanol. We found that BLE had influence on arginine transport (GAP1, CAN1, ALP1, and VBA2 gene) in Saccharomyces cerevisiae (S. cerevisiae), which significantly up-regulated arginine uptake gene expression in vacuole (VBA2 gene) so that inhibited arginine metabolism. Besides, the presence of BLE could improve the overall quality of Chinese yellow rice wine. Consequently, it was worthwhile applying BLE to Chinese rice wine fermentation, especially the wine brewing with S. cerevisiae and Lactobacillus brevis starter.