Comparative genomic analysis of the genus Weissella and taxonomic study of Weissella fangxianensis sp. nov., isolated from Chinese rice wine starter.

In this study, three lactic acid bacteria, namely, HBUAS51963T, HBUAS51964 and HBUAS51965, were isolated from Chinese rice wine starter sampled in Fangxian County, PR China. All were non-motile, non-spore-forming and Gram-positive spherical cells. Their taxonomic status was characterized using a polyphasic approach. Genome-based analysis revealed that all three strains were phylogenomically related to Weissella thailandensis KCTC 3751T and Weissella paramesenteroides ATCC 33313T. The digital DNA-DNA hybridization (dDDH) and average nucleotide identity (ANI) values between the three strains and the phylogenetically related type strains were less than 54.8 and 93.8 %, respectively, and thus, they were below the thresholds of dDDH and ANI for species definition. The genomic DNA G+C content was 38.6 mol %. The predominant fatty acid methyl esters (>10 %) were C16 : 0, C19 : 0 cyc11 and summed feature 10 (C18 : 1 cyc11 and/or ECL 17.834). The polar lipids in the cells of strain HBUAS51963T were mainly phosphatidylglycerol, diphosphatidylglycerol, unidentified glycolipids, phospholipids and lipids. Finally, the three strains were capable of producing d-lactic acid (4.29 g l-1) and various organic acids such as tartaric, acetic, lactic and succinic acids. Overall, the results of genotypic, phenotypic and genomic analyses suggest that the three strains represent a new species of the genus Weissella, for which the name Weissella fangxianis sp. nov. is proposed. The type strain is HBUAS51963T (=GDMCC 1.3506T= JCM 35803T).

Ultra-high-depth macrogenomic sequencing revealed differences in microbial composition and function between high temperature and medium-high temperature Daqu.

Complex microorganisms in Daqu of different temperatures play a vital role in the taste, flavor and quality of Baijiu during fermentation. However, understanding the functional diversity of the whole microbial community between the Daqus of two different temperatures (high temperature Daqu, HD and medium-high temperature Daqu, MD) remains a major challenge. Here, a systematic study of the microbial diversity, functions as well as physiological and biochemical indexes of Daqu are described. The results revealed that the Daqu exhibited unique characteristics. In particular, the diversity of microorganisms in HD and MD was high, with 44 species including 14 novel species (Sphingomonas sp. is the main novel species) detected in all samples. Their profiles of carbohydrate-active enzymes and specific functional components supported the fact that these species were involved in flavor formation. The Daqu microbiome consisted of a high proportion of phage, providing evidence of phage infection/genome integration and horizontal gene transfer from phage to bacteria. Such processes would also regulate Daqu microbiomes and thus flavor quality. These results enrich current knowledge of Daqu and can be used to promote the development of Baijiu fermentation technology.

Low-temperature adaptation and preservation revealed by changes in physiological-biochemical characteristics and proteome expression patterns in post-harvest Hami melon during cold storage.

MAIN CONCLUSION: The proteome and its time-dependent effects reveal the importance of stress response (including expression regulation of heat-shock proteins) and fatty acid metabolism in cold adaptation and preservation of Hami melon. To better understand the molecular mechanism of how Hami melons respond to low-temperature stress, this study investigated the relevant physiological characteristics, catalytic antibody activity, and quantitative proteomics of Hami melon (Jiashi muskmelon) during low-temperature storage. Jiashi muskmelon was stored inside two refrigerators set at 21 °C (control group) and 3 °C, respectively, for 24 days. Low-temperature storage led to a significantly reduced decay rate, weight loss rate, and loss of relative conductivity. It also maintained fruit firmness, inhibited the production rate of malondialdehyde and H2O2, and induced over-expression of antioxidant enzyme and ATPase. A total of 1064 differentially expressed proteins (DEPs) were identified during low-temperature storage. Stimulation response was the main process in response to low-temperature. To further verify the proteome data, we selected four heat-shock proteins (HSP) displaying relatively high expression levels. Real-time fluorescence PCR results confirmed that HmHSP90 I, HmHSP90 II, HmHSP70, and HmsHSP were significantly up-regulated upon low-temperature induction. These proteins may protect the Hami melon from physiological and cellular damage due to the low-temperature stress by acting alone or synergistically. Additionally, the main enrichment term of the fatty acid metabolism-related DEPs was fatty acid beta oxidation at 21 °C in contrast to fatty acid biosynthesis processes at 3 °C. It is speculated that Hami melon enhances low-temperature adaptability by slowing down the oxidative degradation of fatty acids and synthesizing new fatty acids at low temperatures. This study provides new insights into the mechanism of low-temperature adaptation and preservation in post-harvest Hami melon during cold storage.

The Stannum-Ene Reactions of Benzyne and Cyclohexyne with Superb Chemoselectivity for Cyclohexyne.

The stannum-ene reactions of both benzyne and cyclohexyne were realized, which is particularly suitable for cyclohexyne with a broad substrate scope and excellent chemoselectivity. Our DFT calculations via distortion/interaction analysis revealed that both stannum- and hydrogen-ene reactions with cyclohexyne have later transition states due to their higher distortion energies in the transition states than those in benzyne reactions, which lead to enhanced Pauli repulsion as the decisive factor in the interaction energy accompanied with enlarged energy gap between two types of ene reactions. Therefore, excellent chemoselectivity was disclosed in the cyclohexyne-ene reaction.

Aryne 1,4-Disubstitution and Remote Diastereoselective 1,2,4-Trisubstitution via a Nucleophilic Annulation-[5,5]-Sigmatropic Rearrangement Process.

Both aryne 1,4-disubstitution and 1,2,4-trifunctionalization were accomplished from tertiary amines bearing a penta-2,4-dien-1-yl moiety. These transformations could directly incorporate a C-N and a C-C bond para to each other on an aryne intermediate via a sequential nucleophilic addition and [5,5]-sigmatropic rearrangement. When arynes bearing 3-tethered electrophiles were employed, a cascade regioselective nucleophilic addition, intramolecular cyclization, and remote diastereoselective [5,5]-sigmatropic rearrangement process was observed. Our density functional theory (DFT) calculations revealed that hydrogen-bonding interactions between two C-H hydrogens on the penta-2,4-dien-1-yl chain and the oxygen anion generated upon N-nucleophilic annulation reaction in the [5,5]-sigmatropic rearrangement step is responsible for the remote diastereoselective control in this reaction system.

Benzyne 1,2,4-Trisubstitution and Dearomative 1,2,4-Trifunctionalization.

Both 1,2,4-trisubstitution and dearomative 1,2,4-trifunctionalization of benzyne have been accomplished from sulfoxides bearing a penta-2,4-dien-1-yl moiety. These cascade transformations proceed through a benzyne insertion into the S═O bond and an uncommon regiospecific anionic [4,5]-sigmatropic rearrangement, furnishing a C-O, C-S, and C-C bond on the C1-, C2-, and C4-position of a benzene ring, respectively. This study showcases new cascade benzyne reaction modes involving both distal C-H bond functionalization and dearomatization.

Aryne 1,2,3,5-Tetrasubstitution Enabled by 3-Silylaryne and Allyl Sulfoxide via an Aromatic 1,3-Silyl Migration.

Although benzyne has been well-known to serve as a synthon that can conveniently prepare various 1,2-difunctionalized benzenes, the sites other than its formal triple bond remain silent in typical benzyne transformations. An unprecedented aryne 1,2,3,5-tetrasubstitution was realized from 3-silylbenzyne and aryl allyl sulfoxide, the mechanistic pathway of which includes a regioselective aryne insertion into the S═O bond, a [3,6]-sigmatropic rearrangement, and a thermal aromatic 1,3-silyl migration cascade.

An Organic Hybrid Indium-Telluride Incorporating Binuclear Complexes [In2(ea)4]2+ with a Bridging Oxygen Donor.

The new organic hybrid indium-telluride [In2(ea)2Te2]n (1; Hea = ethanolamine) exhibits a new type of one-dimensional polymeric chain based on the linkages of dinuclear [In2(ea)4]2+ and [In2Te4]2- units, which offers the first example of an indium-telluride framework incorporating binuclear complexes [In2(ea)4]2+ with a bridging O donor. 1 shows a distinctive photocurrent response and photocatalytic properties under visible-light illumination.

iTRAQ-based quantitative proteomics analysis of cantaloupe (Cucumis melo var. saccharinus) after cold storage.

BACKGROUND: Cantaloupe is susceptible to cold stress when it is stored at low temperatures, resulting in the loss of edible and commercial quality. To ascertain the molecular mechanisms of low temperatures resistance in cantaloupe, a cold-sensitive cultivar, Golden Empress-308 (GE) and a cold-tolerant cultivar, Jia Shi-310 (JS), were selected in parallel for iTRAQ quantitative proteomic analysis. RESULTS: The two kinds of commercial cultivars were exposed to a temperature of 0.5 °C for 0, 12 and 24 days. We found that the cold-sensitive cultivar (GE) suffered more severe damage as the length of the cold treatment increased. Proteomic analysis of both cultivars indicated that the number of differentially expressed proteins (DEPs) changed remarkably during the chilly treatment. JS expressed cold-responsive proteins more rapidly and mobilized more groups of proteins than GE. Furthermore, metabolic analysis revealed that more amino acids were up-regulated in JS during the early phases of low temperatures stress. The DEPs we found were mainly related to carbohydrate and energy metabolism, structural proteins, reactive oxygen species scavenging, amino acids metabolism and signal transduction. The consequences of phenotype assays, metabolic analysis and q-PCR validation confirm the findings of the iTRAQ analysis. CONCLUSION: We found that the prompt response and mobilization of proteins in JS allowed it to maintain a higher level of cold tolerance than GE, and that the slower cold responses in GE may be a vital reason for the severe chilling injury commonly found in this cultivar. The candidate proteins we identified will form the basis of future studies and may improve our understanding of the mechanisms of cold tolerance in cantaloupe.

High-throughput Sequencing-based Analysis of Microbial Diversity in Rice Wine Koji from Different Areas.

Rice wine, a traditional fermented alcoholic beverage in China, is produced with grains such as rice, which are fermented with saccharifying starter-koji. Its flavor quality is closely associated to the starter culture-koji, which is made by mixing botanical materials with high-class glutinous rice in certain ecological context. However, there are few reports on the microbial community structure of rice wine koji. In this paper, bacterial community structures of rice wine koji were analyzed using 16S rRNA gene sequencing based on Illumina MiSeq high-throughput technology in 20 samples collected from Xiaogan area, Hubei province and Dazhu area, Sichuan province (10 from each area). We found rice wine koji flora mainly consisted of Weissella, Lactobacillus, Lactococcus, Bacillus, Enterococcus, and Cronobacter, with relative abundances of 29.49%, 10.93%, 8.85%, 4.75%, 1.16% and 1.15%, respectively, as well as an accumulative average relative abundance of 58.71%. They all belonged to Firmicutes and Proteobacteria-the two known dominant genus. Genus-level PCA (Principal component analysis) and OTU-level PCoA (Principal coordinates analysis) based on unweighted UniFrac distances showed that the bacterial community structure differed significantly between the samples from the 2 areas. 7 OTUs were detected in all samples, accounting for 4.4% of the total qualified assembly. Among the 7 OTUs, 3 OTUs were identified as Enterococcus, 2 OTUs were identified as Cronobacter, 1 OTU was identified as Bacillus and 1 OTU was identified as Alkaliphilus. Fifty-eight lactic acid bacteria (LAB) strains were isolated from the 20 koji samples with traditional microbial methods. Among them, Enterococcus faecium and Pediococcus pentosaceus were the dominant LAB isolates, with relative abundances of 51.72% and 31.03%. Despite the differences, a large number of shared bacteria were detected in samples from the two areas.

Theoretical Study of the Addition of Cu-Carbenes to Acetylenes to Form Chiral Allenes.

Terminal alkynes have become one of the most versatile building blocks for C-C bond construction in the past few decades, and they are usually considered to convert to acetylides before further transformations. In this study, a novel direct nucleophilic addition mode for Cu(I)-catalyzed cross-coupling of terminal alkynes and N-tosylhydrazones to synthesize chiral allenes is proposed, and it was investigated by density functional theory with the M11-L density functional. Three different reaction pathways were considered and investigated. The computational results show that the proposed reaction pathway, which includes direct nucleophilic attack of protonated acetylene, deprotonation of the vinyl cation, and catalyst regeneration, is the most favorable pathway. Another possible deprotonation-carbenation-insertion pathway is shown to be unfavorable. The direct nucleophilic addition step is the rate- and enantioselectivity-determining step in the catalytic cycle. Noncovalent interaction analysis shows that the steric effect between the methyl group of the carbene moiety and the naphthalyl group of the bisoxazoline ligand is important to control the enantioselectivity. In addition, calculation of a series of chiral bisoxazoline ligands shows that a bulky group on the oxazoline ring is favorable for high enantioselectivity, which agrees with experimental observations. Moreover, copper acetylides are stable, and their generation is a favorable pathway in the absence of chiral bisoxazoline ligands.

Mechanistic view of Ru-catalyzed C-H bond activation and functionalization: computational advances.

Ru-Catalyzed aromatic C-H bond activation and functionalization have emerged as important topics because they have resulted in remarkable progress in organic synthesis. Both experimental and theoretical studies of their mechanisms are important for the design of new synthetic methodologies. In this review, a mechanistic view of the Ru-mediated C-H bond cleavage step is first given to reveal the C-H bond activation modes, including oxidative addition, metathesis and base-assisted deprotonation. In this process, directing groups play an important role in determining the reactivity of the C-H bond. The C-H bond activation generally leads to the formation of a Ru-C bond, which is further functionalized in the subsequent steps. The mechanisms of Ru-catalyzed arylation, alkylation, and alkenylation of arenes are summarized, and these transformations can be categorized into cross-coupling with electrophiles or oxidative coupling with nucleophiles. In addition, the mechanism of ortho-ruthenation-enabled remote C-H bond functionalization is also discussed.

One-pot synthesis of ß-lactams by the Ugi and Michael addition cascade reaction.

Diversity-oriented synthesis of ß-lactams was achieved via Ugi/Michael reaction cascades under mild conditions. The intramolecular hydrogen bonding between the heteroatom from an aldehyde component and the amide NH group controls the chemoselectivity of the Michael reaction versus the aza-Michael reaction. DFT calculation was performed to clarify the mechanism, chemo-selectivity and diastereoselectivity of this work. This one-pot protocol offers a straightforward method to build a diversified ß-lactam library for drug discovery.

Organocatalytic Atroposelective Intramolecular [4+2] Cycloaddition: Synthesis of Axially Chiral Heterobiaryls.

The enantioselective construction of axially chiral aryl-naphthopyran skeletons was realized by organocatalytic atroposelective intramolecular [4+2] cycloaddition of in situ generated vinylidene ortho-quinone methides, from 2-ethynylphenol derivatives, with alkynes. Through this method, the heteroatropisomers were obtained with excellent yields and enantioselectivities. Moreover, a speculative model of the stereochemical outcome is proposed based on preliminary mechanistic studies. The products having various functional groups can be easily transformed into valuable intermediates as either potential ligands or organocatalysts.

Mechanism, Regio-, and Diastereoselectivity of Rh(III)-Catalyzed Cyclization Reactions of N-Arylnitrones with Alkynes: A Density Functional Theory Study.

Nitrones have been used for rhodium-catalyzed cyclization C-H bond activation and O atom transfer of arylnitrones with alkynes by Chang et al. ( J. Am. Chem. Soc. 2015 , 137 , 4908 - 4911 ). Density functional theory method has been used to study the mechanism, regio-, and diastereoselectivity of type reactions. The results elucidated that the reaction pathway for Rh(III)-catalyzed cyclization of N-arylnitrones with alkyne contains a C-H bond activation, an alkyne insertion into Rh-C bond, a reductive elimination to form a Rh(I) complex, an oxidative addition leading to N-O cleavage, an imine insertion into the Rh-C bond, and the final protonolysis to regenerate the products and the active catalyst. The regioselectivity of this reaction with asymmetric alkyne is controlled by the electronic effect in alkyne insertion type instead of steric effects. The distortion-interaction analysis is also used to explain the regioselectivity. The diastereoselectivity is controlled by the imine insertion step. In this step, the sterically less hindered transition state is favored, leading to stereoselective product formation.

Mechanism of Rhodium-Catalyzed Formyl Activation: A Computational Study.

Metal-catalyzed transfer hydroformylation is an important way of cleaving C-C bonds and constructing new double bonds. The newly reported density functional theory (DFT) method, M11-L, has been used to clarify the mechanism of the rhodium-catalyzed transfer hydroformylation reported by Dong et al. DFT calculations depict a deformylation and formylation reaction pathway. The deformylation step involves an oxidative addition to the formyl C-H bond, deprotonation with a counterion, decarbonylation, and ß-hydride elimination. After olefin exchange, the formylation step takes place via olefin insertion into the Rh-H bond, carbonyl insertion, and a final protonation with the conjugate acid of the counterion. Theoretical calculations indicate that the alkalinity of the counterion is important for this reaction because both deprotonation and protonation occur during the catalytic cycle. A theoretical study into the formyl acceptor shows that the driving force of the reaction is correlated with the stability of the unsaturated bond in the acceptor. Our computational results suggest that alkynes or ring-strained olefins could be used as formyl acceptors in this reaction.

Asymmetric Transfer Hydrogenation of Imines using Alcohol: Efficiency and Selectivity are Influenced by the Hydrogen Donor.

The influence of the alcohol, as the hydrogen donor, on the efficiency and selectivity of the asymmetric transfer hydrogenation (ATH) of imines is reported for the first time. This discovery not only leads to a highly enantioselective access to N-aryl and N-alkyl amines, but also provides new insight into the mechanism of the ATH of imines. Both experimental and computational studies provide support for the reaction pathway involving an iridium alkoxide as the reducing species.

Comparative analysis of sensory features, microbial diversity, and their correlations in light-flavor Daqu from different regions.

This study performed a comparative analysis of the sensory and microbial profiles of light-flavor Bijou (LFD) from Taiyuan (Shanxi Province) and Suizhou (Hubei Province) in China. The results of the electronic nose showed that the aromatic substances of the LFD from Taiyuan (TLFD) were significantly higher (p < .05), while alcohol and aldehyde substances were significantly lower (p < .05) compared with the LFD from Suizhou (SLFD). The average response values of sensors W1C (sensitive to aromatic hydrocarbons), W3C (sensitive to amine and aromatic components), W5C (sensitive to olefins, aromatics, and polar molecules), and W2S (sensitive to alcohol and aldehyde compounds) to TLFD were 0.26, 0.33, 0.34, and 7.72, whereas the response values to SLFD were 0.25, 0.32, 0.33, and 8.04, respectively. The electronic tongue results showed that the aftertaste A (bitter aftertaste) and aftertaste B (astringent aftertaste) of the TLFD were significantly higher (p < .05) and umami was significantly lower (p < .05) as compared to the SLFD. The relative intensities of the aftertaste A, aftertaste B, and umami indicators of TLFD were 0.10, -0.008, and -0.22, respectively, while those of SLFD were -0.23, -0.36, and 0.835, respectively. MiSeq high-throughput sequencing results showed that TLFD exhibited lower fungal richness and diversity compared to SLFD. The dominant bacterial genera were mainly Bacillus (58.12%), Kroppenstedtia (10.11%), and Weissella (6.26%), and the dominant fungal genera were Saccharomycopsis (67.53%), Rasamsonia (9.90%), and Thermoascus (7.10%). Streptomyces and Staphylococcus were identified as the key characteristic microorganisms in TLFD, while Kroppenstedtia, Rasamsonia, and Thermoascus were the key characteristic microorganisms in SLFD. Correlation analysis indicated a stronger correlation between microorganisms and sensory characteristics in SLFD samples. This study provides valuable insights into the sensory and microbiological characteristics of LFD from different regions and offers a new perspective for understanding the production of differently flavored light-flavor Baijiu.

Exploring jujube wine flavor and fermentation mechanisms by HS-SPME-GC-MS and UHPLC-MS metabolomics.

The fermentation metabolites significantly influence the quality of jujube wine. However, the dynamics of these metabolites during fermentation are not well understood. In this study, a total of 107 volatile and 1758 non-volatile compounds were identified using a flavor-directed research strategy and non-targeted metabolomics. The increase in esters and alcohols during fermentation shifted the aroma from grassy, mushroomy, and earthy to a floral and fruity flavor in the jujube wine. Leucine and phenylalanine were notably enriched during fermentation, potentially benefiting human health and enriching the flavor of fruit wines. Moreover, pathway analysis identified four key metabolic pathways and two crucial metabolic substrates, pyruvate and l-aspartate. This study provides a theoretical reference for optimizing the fermentation process and enhancing the quality of jujube wine.