Influence of microbiota and metabolites on the quality of tobacco during fermentation

Fungal communities are more sensitive to mildew than bacterial communities during tobacco storage processes

Mildew poses a significant threat to tobacco production; however, there is limited information on the structure of the abundant and rare microbial subcommunities in moldy tobacco leaves. In this study, we employed high-throughput sequencing technology to discern the disparities in the composition, diversity, and co-occurrence patterns of abundant and rare fungal and bacterial subcommunities between moldy and normal tobacco leaves collected from Guizhou, Shanghai, and Jilin provinces, China. Furthermore, we explored the correlation between microorganisms and metabolites by integrating the metabolic profiles of moldy and normal tobacco leaves. The results showed that the fungi are more sensitive to mildew than bacteria, and that the fungal abundant taxa exhibit greater resistance and environmental adaptability than the rare taxa. The loss of rare taxa results in irreversible changes in the diversity, richness, and composition of the fungal community. Moreover, rare fungal taxa and abundant bacterial taxa played crucial roles in maintaining the stability and functionality of the tobacco microecosystem. In moldy tobacco, however, the disappearance of rare taxa as key nodes resulted in reduced connectivity and stability within the fungal network. In addition, metabolomic analysis showed that the contents of indoles, pyridines, polyketones, phenols, and peptides were significantly enriched in the moldy tobacco leaves, while the contents of amino acids, carbohydrates, lipids, and other compounds were significantly reduced in these leaves. Most metabolites showed negative correlations with Dothideomycetes, Alphaproteobacteria, and Gammaproteobacteria, but showed positive correlations with Eurotiales and Bacilli. This study has demonstrated that abundant fungal taxa are the predominant biological agents responsible for tobacco mildew, while bacteria may indirectly contribute to this process through the production and degradation of metabolites. KEY POINTS: • Fungi exhibited greater sensitivity to mildew of tobacco leaf compared to bacteria • Rare fungal taxa underwent significant damage during the mildew process • Mildew may damage the defense system of the tobacco leaf microecosystem.

Effects of Bacillus altitudinis inoculants on cigar tobacco leaf fermentation

Introduction

Microbial succession and metabolic adjustment during cigar tobacco leaf (CTL) fermentation are key factors to improve the quality and flavor of CTLs. However, the interactions in the above processes remain to be further elucidated.

Methods

Bacillus altitudinis inoculants were added to the CTLs, and metagenomics and metabolomics were used to analyze the effects of the inoculants on regulating microbial succession, metabolic shift, and aroma production during fermentation.

Results and discussion

The addition of the inoculants reinforced the CTL macromolecule transformation and facilitated the aroma production efficiently, and the total aroma production was increased by 43% compared with natural fermentation. The omics analysis showed that Staphylococcus was a main contributor to fatty acid degradation, inositol phosphate metabolism, energy supply (oxidative phosphorylation), nutrient transport (ABC transporter and phosphotransferase system [PTS]), and aroma production (terpenoid backbone biosynthesis, phenylalanine metabolism, and degradation of aromatic compounds). Furthermore, Staphylococcus was positively correlated with TCA cycle intermediates (citric acid, fumaric acid, and aconitic acid), cell wall components, peptidoglycan intermediates (GlcNAc-1-P and UDP-GlcNAc), and phytic acid degradation products (inositol). The characteristics collectively showed Staphylococcus to be the most dominant in the microbial community at the genus level during microflora succession. The addition of the inoculants supplemented the nutritional components of the CTLs, enhanced the metabolic activity and diversity of bacteria such as Corynebacterium, improved their competitive advantages in the microflora succession, and facilitated the richness of microbial communities. Additionally, a metabolic shift in nicotine degradation and NAD + anabolism from Staphylococcus to Corynebacterium in fermentation with inoculants was first observed. Meanwhile, the significantly correlative differential metabolites with Staphylococcus and Corynebacterium were a metabolic complement, thus forming a completely dynamic fermentation ecosystem. The results provided evidence for CTL fermentation optimization.

Degradation and mechanism analysis of protein macromolecules by functional bacteria in tobacco leaves

Tobacco, a crop of significant economic importance, was greatly influenced in leaf quality by protein content. However, current processing parameters fail to adequately meet the requirements for protein degradation. Microorganisms possess potential advantages for degrading proteins and enhancing the quality of tobacco leaves, and hold substantial potential in the process of curing. To effectively reduce the protein content in tobacco leaves, thereby improving the quality and safety of the tobacco leaves. In this study, tobacco leaf were used as experimental material. From these, the BSP1 strain capable of effectively degrading proteins was isolated and identified as Bacillus subtilis by 16S rDNA analysis. Furthermore, the mechanisms were analyzed by integrating microbiome, transcriptome, and metabolome. Before curing, BSP1 was applied to the surface of tobacco leaves. The results indicated that BSP1 effectively improves the activity of key enzymes and the content of related substances, thereby enhancing protein degradation. Additionally, protein degradation was achieved by regulating the diversity of the microbial community on the surface of the tobacco leaves and the ubiquitin-proteasome pathway. This study provided new strategies for extracting and utilizing functional strains from tobacco leaves, opening new avenues for enhancing the quality of tobacco leaves.

Optimization of liquid fermentation conditions for Coprinus comatus to enhance antioxidant activity

Coprinus comatus is an edible and medicinal fungus. In this study, the antioxidant activity of the fermentation product of C. comatus was investigated through optimization of fermentation process. The results indicated that the fermentation product of C. comatus had obvious scavenging ability for 2,2'-Azino-bis(3-ethylbenzothiazoline)-6-sulphonic acid (ABTS) free radical. The EC50 of the n-butanol extract from the fermentation product on ABTS·+ was 0.65 ± 0.02 mg/mL. On this basis, the liquid fermentation conditions of C. comatus were optimized through single factor and response surface optimization experiments according to the scavenging ability of ABTS·+ to improve the antioxidant capacity of the fermentation product. The results showed that when the 14% of C. comatus was fermented in a culture medium with a C/N ratio of 48:1 for 6 days, the ABTS·+ scavenging ability was the strongest, and the EC50 of n-butanol extract was 0.57 ± 0.01 mg/mL, which was 12.31% higher than the initial activity. This study laid the foundation for the development of C. comatus.

Effect of Lentinus sajor-caju on the chemical composition and antioxidant activity of highland barley straw under solid-state fermentation

Introduction

The efficient utilization of straw resources as animal feed has gained considerable attention. The objective of this study was to evaluate whether Lentinus sajor-caju treatment alters the chemical composition and antioxidant activity of highland barley straw and enhances its functional value as a ruminant feed.

Methods

The chemical composition, antioxidant capacity, and metabolomic profile of highland barley straw were determined after 21 days of solid-state fermentation with L. sajor-caju at 25°C. The differential metabolites between fermented and unfermented highland barley straw were identified by LC-MS and the relationship between the identified metabolites and antioxidant capacity was elucidated.

Results

The results showed that, compared with untreated highland barley straw, the crude protein and ether extract contents were higher (51.55 and 76.43%, respectively) in highland barley straw after 21 days of incubation with L. sajor-caju, whereas the hemicellulose, cellulose, and acid detergent lignin contents were lower (2.48, 25.08, and 45%, respectively). The total antioxidant capacity was significantly higher in L. sajor-caju-treated than in untreated highland barley straw. In total, 600 differential metabolites (301 upregulated and 299 downregulated) were identified between L. sajor-caju-fermented and unfermented highland barley straw. Correlation analysis results showed that Fe2+ scavenging and total phenolic content were strongly correlated with total antioxidant capacity. Meanwhile, the differential flavonoid metabolites between fermented and unfermented highland barley straw were primarily associated with antioxidant activity, with kaempferol 3-xylosylglucoside, isoginkgetin, and rhoifolin being the most representative.

Conclusion

Thus, this study demonstrates that L. sajor-caju could enhance the functional value of highland barley straw, showing the potential of L. sajor-caju for improving the utilization of agricultural straws in ruminants.

Enhancing the quality of fermented plant leaves: the role of metabolite signatures and associated fungi

Fungi play a pivotal role in fermentation processes, influencing the breakdown and transformation of metabolites. However, studies focusing on the effects of fungal-metabolite correlations on leaf fermentation quality enhancement are limited. This study investigated specific metabolites and fungi associated with high- and low-quality fermented plant leaves. Their changes were monitored over fermentation periods of 0, 8, 16, and 24 days. The results indicated that organoheterocyclic compounds, lipids, lipid-like molecules, organic nitrogen compounds, phenylpropanoids, and polyketides were predominant in high-quality samples. The fungi Saccharomyces (14.8%) and Thermoascus (4.6%) were predominantly found in these samples. These markers exhibited significant changes during the 24-day fermentation period. The critical influence of fungal community equilibrium was demonstrated by interspecies interactions (e.g., between Saccharomyces and Eurotium). A co-occurrence network analysis identified Saccharomyces as the primary contributor to high-quality samples. These markers collectively enhance the quality and sensory characteristics of the final product.

Application of pectin hydrolyzing bacteria in tobacco to improve flue-cured tobacco quality

To study the relationship between the diversity of the surface microbial community and tobacco flavor, and to improve tobacco quality using microorganisms. The microbial community composition and diversity of 14 samples of flue-cured tobacco from tobacco-producing areas in Yunnan with varying grades were analyzed by high-throughput sequencing. PICRUSt was used for predicting microbial functions. A strain of Bacillus amyloliquefaciens W6-2 with the ability to degrade pectin was screened from the surface of flued-cured tobacco leaves from Yunnan reroasted tobacco leave. The enzyme preparation was prepared through fermentation and then applied for treating flue-cured tobacco. The improvement effect was evaluated by measuring the content of macromolecule and the changes in volatile components, combined with sensory evaluations. The bacterial communities on the surface of flue-cured tobacco exhibited functional diversity, consisting primarily of Variovorax, Pseudomonas, Sphingomonas, Burkholderia, and Bacillus. These bacterial strains played a role in the aging process of flue-cured tobacco leaves by participating in amino acid metabolism and carbohydrate metabolism. These metabolic activity converted complex macromolecules into smaller molecular compounds, ultimately influence the smoking quality and burning characteristics of flue-cured tobacco. The pectinase preparation produced through fermentation using W6-2 has been found to enhance the aroma and sweetness of flue-cured tobacco, leading to improved aroma, reduced impurities, and enhanced smoothness. Additionally, the levels of pectin, cellulose, and hemicellulose decreased, while the levels of water-soluble sugar and reducing sugar increased, and the contents of esters, ketones, and aldehydes increased, and the contents of benzoic acid decreased. The study revealed the correlation between surface microorganisms and volatile components of Yunnan tobacco leaves, and the enzyme produced by the pectin-degrading bacteria W6-2 effectively improved the quality of flue-cured tobacco.

Enhanced delignification and production of bioactive compounds in wheat straw by optimizing sterilization methods for Irpex lacteus fermentation

This study aimed to examine the effects of sterilization methods on the degradation ability and bioactive compound production of Irpex lacteus in wheat straw. Following 28 days of fermentation, the lignin content of samples autoclaved and pasteurized at pH 4.5 was reduced by 16.0 % - 21.7 % compared to pasteurized samples without pH adjustment, accompanied by a significant increase in sugar yield ranging from 83.30 % - 96.35 %. Autoclaved samples exhibited the lowest total phenol content and antioxidant activity (P < 0.05). Bacillus occupied an absolute advantage (89.1 %) in samples pasteurized at pH 4.5, whereas 10 bacterial genera exhibited abundances above 1 % in pasteurized samples without pH adjustment. Furthermore, 45.1 % - 47.2 % of the metabolites comprised lipids and lipid-like molecules, and some of them were improved by pasteurization at pH 4.5. Overall, pasteurization at acidic conditions is an effective sterilization method for the fungal conversion of wheat straw.

Solid-State Fermentation Improves Tobacco Leaves Quality via the Screened Bacillus subtilis of Simultaneously Degrading Starch and Protein Ability

The process of tobacco aging plays a significant role in enhancing the smoking experience by improving the flavor and quality of tobacco leaves. During natural aging, the metabolic activity of the microbes on the surface of tobacco leaves will be greatly changed. Besides, starch and protein are two of the main macromolecular compounds causing the poor smoking quality of tobacco leaves which to be degraded for better tobacco quality. In this study, a bacterium with the simultaneously degrading ability of starch (degradation rate of 33.87%) and protein (degradation rate of 20%) has been screened out from high-class tobacco leaf and then inoculated into low-class tobacco leaf by solid-state fermentation for quality improvement. The changes in components related to carbon and nitrogen showed that the strain had an obvious effect on the quality improvement of tobacco leaves. After that, GC-MS analyses displayed the volatile flavor compounds which become rich and the flavor has been improved. It has been proved that inoculation solid-state fermentation by dominant strain could improve tobacco quality, as well as instead of the traditional natural aging process which greatly shortens the aging process. The work also offers a helpful strategy for solid-state products for deep fermentation.

Evaluation of Six Aromatic Amines in the Mainstream Smoke of Commercial Cigars

Aromatic amines are a class of carcinogenic compounds present in tobacco smoke that are listed on the U.S. Food and Drug Administration (FDA) list of harmful and potentially harmful constituents (HPHCs) in tobacco products and tobacco smoke. The yields of six aromatic amines (1-aminonaphthalene [1-AN], 2-aminonaphthalene [2-AN], 3-aminobiphenyl [3-ABP], 4-aminobiphenyl [4-ABP], ortho-toluidine [o-TOL], and o-anisidine [o-ANI]) in the mainstream smoke from 23 commercial filtered cigars, 16 cigarillos, and 11 large cigars were determined using solid-phase microextraction coupled to gas chromatography triple quadrupole mass spectrometry (SPME headspace GC-MS/MS). The commercial cigars were smoked under the Cooperation Centre for Scientific Research Relative to Tobacco (CORESTA) Recommended Method 64 using a linear cigar smoking machine. The aromatic amine yields in the mainstream smoke from 50 commercial cigars show high levels of variation within and between the products. The average yields of the aromatic amines in the filtered cigars, cigarillos, and large cigars were 108, 371, and 623 ng/cigar for o-TOL; 6, 14, and 22 ng/cigar for o-ANI; 65, 114, and 174 ng/cigar for 1-AN; 25, 59, and 87 ng/cigar for 2-AN; 6, 17, and 27 ng/cigar for 3- ABP; and 8, 11, and 17 ng/cigar for 4-ABP, respectively. The relationships between aromatic amines and (1) total particulate matter (TPM), (2) water-soluble proteins, and (3) water-insoluble proteins were evaluated. We found that the aromatic amines showed a good linear response with TPM on a per cigar basis and showed significant positive correlations with proteins. In addition, the water-insoluble proteins make a greater contribution to the formation of aromatic amines compared to the water-soluble proteins.

Microbial community and chemical composition of cigar tobacco (Nicotiana tabacum L.) leaves altered by tobacco wildfire disease

Tobacco wildfire disease caused by Pseudomonas syringae pv. tabaci is one of the most destructive foliar bacterial diseases occurring worldwide. However, the effect of wildfire disease on cigar tobacco leaves has not been clarified in detail. In this study, the differences in microbiota and chemical factors between wildfire disease-infected leaves and healthy leaves were characterized using high-throughput Illumina sequencing and a continuous-flow analytical system, respectively. The results demonstrated significant alterations in the structure of the phyllosphere microbial community in response to wildfire disease, and the infection of P. syringae pv. tabaci led to a decrease in bacterial richness and diversity. Furthermore, the content of nicotine, protein, total nitrogen, and Cl- in diseased leaves significantly increased by 47.86%, 17.46%, 20.08%, and 72.77% in comparison to healthy leaves, while the levels of total sugar and reducing sugar decreased by 59.59% and 70.0%, respectively. Notably, the wildfire disease had little effect on the content of starch and K+. Redundancy analysis revealed that Pseudomonas, Staphylococcus, Cladosporium, and Wallemia displayed positive correlations with nicotine, protein, total nitrogen, Cl- and K+ contents, while Pantoea, Erwinia, Sphingomonas, Terrisporobacter, Aspergillus, Alternaria, Sampaiozyma, and Didymella displayed positive correlations with total sugar and reducing sugar contents. Brevibacterium, Brachybacterium, and Janibacter were found to be enriched in diseased leaves, suggesting their potential role in disease suppression. Co-occurrence network analysis indicated that positive correlations were prevalent in microbial networks, and the bacterial network of healthy tobacco leaves exhibited greater complexity compared to diseased tobacco leaves. This study revealed the impact of wildfire disease on the microbial community and chemical compositions of tobacco leaves and provides new insights for the biological control of tobacco wildfire disease.

From cultivation to cancer: formation of N-nitrosamines and other carcinogens in smokeless tobacco and their mutagenic implications

Tobacco use is a major cause of preventable morbidity and mortality globally. Tobacco products, including smokeless tobacco (ST), generally contain tobacco-specific N-nitrosamines (TSNAs), such as N'-nitrosonornicotine (NNN) and 4-(methylnitrosamino)-1-(3-pyridyl)-butanone (NNK), which are potent carcinogens that cause mutations in critical genes in human DNA. This review covers the series of biochemical and chemical transformations, related to TSNAs, leading from tobacco cultivation to cancer initiation. A key aim of this review is to provide a greater understanding of TSNAs: their precursors, the microbial and chemical mechanisms that contribute to their formation in ST, their mutagenicity leading to cancer due to ST use, and potential means of lowering TSNA levels in tobacco products. TSNAs are not present in harvested tobacco but can form due to nitrosating agents reacting with tobacco alkaloids present in tobacco during certain types of curing. TSNAs can also form during or following ST production when certain microorganisms perform nitrate metabolism, with dissimilatory nitrate reductases converting nitrate to nitrite that is then released into tobacco and reacts chemically with tobacco alkaloids. When ST usage occurs, TSNAs are absorbed and metabolized to reactive compounds that form DNA adducts leading to mutations in critical target genes, including the RAS oncogenes and the p53 tumor suppressor gene. DNA repair mechanisms remove most adducts induced by carcinogens, thus preventing many but not all mutations. Lastly, because TSNAs and other agents cause cancer, previously documented strategies for lowering their levels in ST products are discussed, including using tobacco with lower nornicotine levels, pasteurization and other means of eliminating microorganisms, omitting fermentation and fire-curing, refrigerating ST products, and including nitrite scavenging chemicals as ST ingredients.

Effects of fermentation chamber temperature on microbes and quality of cigar wrapper tobacco leaves

The natural fermentation of cigar tobacco leaves usually utilizes natural temperature and humidity for fermentation. Cigars produced in China are often fermented in winter, and the low environmental temperatures can lead to slow heating of the tobacco stack, affecting the cigar tobacco leaves quality. This study aimed to determine the minimum chamber temperature required to initiate the process of fermentation for cigar tobacco leaves and to explore the impact of temperature on the microbial community of tobacco leaves. Here, the cigar variety "Dexue 1" were subjected to stacking fermentation under three temperature parameters (20 ℃, 27 ℃, 34 ℃). With an increase in environmental temperature, the temperature inside the stack of cigar leaves increased significantly, the protein, total sugar, starch, and total alkaloid content in fermented tobacco leaves decreased, and the aroma components and amino acid content increased. Microbial richness and community diversity associated with fermented tobacco were highest at chamber temperatures of above 27 ℃. The relative abundance of Chryseobacterium and Rhodococcus was significantly negatively correlated with protein, alkaloids, total sugar, and starch, and positively correlated with amino acids and aroma components. Chryseobacterium and Rhodococcus may be responsible for the degradation of macromolecular substances and the conversion of favorable aromatic substances, thus improving the tobacco leaves quality. This study demonstrated that increasing the fermentation chamber temperature above 27 ℃ was conductive to raising the inner-stack temperature, increased microbial diversity and aromatic quality, reduced the strength and irritation, and extremely enhanced the overall quality of fermented cigar tobacco leaves. KEY POINTS: • The environmental temperature of the fermentation chamber has a significant impact on the quality of tobacco • Temperature > 27 ℃ can initiate the process of cigar tobacco leaves fermentation and increase inner-stack temperature and microbial diversity and abundance • Chryseobacterium and Rhodococcus may be related to the degradation of macromolecular substances and the transformation of aromatic substances, thereby improving the quality of tobacco leaves.

The bacterial succession and its role in flavor compounds formation during the fermentation of cigar tobacco leaves

Fermentation is the key process required for developing the characteristic properties of cigar tobacco leaves, complex microorganisms are involved in this process. However, the microbial fermentation mechanisms during the fermentation process have not been well-characterized. This study investigated the dynamic changes in conventional chemical composition, flavor compounds, and bacterial community during the fermentation of cigar tobacco leaves from Hainan and Sichuan provinces in China, as well as the potential roles of bacteria. Fermentation resulted in a reduction of conventional chemical components in tobacco leaves, with the exception of a noteworthy increase in insoluble protein content. Furthermore, the levels of 10 organic acids and 19 amino acids showed a significant decrease, whereas the concentration of 30 aromatic substances exhibited a unimodal trend. Before fermentation, the bacterial community structures and dominant bacteria in Hainan and Sichuan tobacco leaves differed significantly. As fermentation progressed, the community structures in the two regions became relatively similar, with Delftia, Ochrobactrum, Rhodococcus, and Stenotrophomonas being dominant. Furthermore, a total of 12 functional bacterial genera were identified in Hainan and Sichuan tobacco leaves using bidirectional orthogonal partial least squares (O2PLS) analysis. Delftia, Ochrobactrum, and Rhodococcus demonstrated a significant negative correlation with oleic acid and linoleic acid, while Stenotrophomonas and Delftia showed a significant negative correlation with undesirable amino acids, such as Ala and Glu. In addition, Bacillus showed a positive correlation with benzaldehyde, while Kocuria displayed a positive correlation with 2-acetylfuran, isophorone, 2, 6-nonadienal, and β-damascenone. The co-occurrence network analysis of microorganisms revealed a prevalence of positive correlations within the bacterial network, with non-abundant bacteria potentially contributing to the stabilization of the bacterial community. These findings can improve the overall tobacco quality and provide a novel perspective on the utilization of microorganisms in the fermentation of cigar tobacco leaves.

Phenylalanine-mediated changes in the soil bacterial community promote nitrogen cycling and plant growth

Soil amino acids (AAs) are the most active components of soil N, which can be mineralized or absorbed by bacteria as N and C sources. We hypothesized that exogenous AAs could regulate the bacterial community and affect soil N cycling, and the effect sizes could vary depending on individual AAs. Here, we applied feather (keratin)-based compost rich in AAs to Poncirus trifoliata (L.) to evaluate the regulation of bacterial community by AAs; furthermore, we applied six individual AAs to test their effects. The compost significantly increased soil hydrolysable AA content, ammonia monooxygenase gene abundance, and plant growth and changed bacterial community structure. Redundancy analysis revealed that the effects of AAs on the bacterial community composition were greater than those of soil chemical properties, and phenylalanine (Phe) was the most effective among thirteen individual AAs. When applied individually, Phe caused the greatest increase in N cycling-related enzyme activity and plant growth and most significantly altered the bacterial community structure among the six exogenous AAs. Notably, Phe significantly increased the relative abundances of Burkholderia-Caballeronia-Paraburkholderia, Azospirillum, Cupriavidus, and Achromobacter, whose abundances were significantly positively correlated with plant biomass, and significantly reduced the relative abundances of Arachidicoccus, Pseudopedobacter, Sphingobacterium, and Paenibacillus, whose abundances were significantly negatively correlated with plant biomass. We demonstrate that soil AAs strongly shape the bacterial community. Particularly, Phe enhances N cycling and plant growth by increasing the potentially beneficial bacterial taxa and inhibiting the potentially harmful bacterial taxa, which needs further validation.

Microbial and enzymatic changes in cigar tobacco leaves during air-curing and fermentation

Metabolic enzyme activity and microbial composition of the air-curing and fermentation processes determine the quality of cigar tobacco leaves (CTLs). In this study, we reveal the evolution of the dominant microorganisms and microbial community structure at different stages of the air-curing and fermentation processes of CTLs. The results showed that the changes in metabolic enzymes occurred mainly during the air-curing phase, with polyphenol oxidase (PPO) being the most active at the browning phase. Pseudomonas, Bacteroides, Vibrio, Monographella, Bipolaris, and Aspergillus were the key microorganisms in the air-curing and fermentation processes. Principal coordinate analysis revealed significant separation of microbial communities between the air-curing and fermentation phases. Redundancy analysis showed that bacteria such as Proteobacteria, Firmicutes, Bacteroidota, and Acidobacteriota and fungi such as Ascomycota and Basidiomycota were correlated with enzyme activity and temperature and humidity. Bacteria mainly act in sugar metabolism, lipid metabolism, and amino acid metabolism, while fungi mainly degrade lignin, cellulose, and pectin through saprophytic action. Spearman correlation network analysis showed that Firmicutes, Proteobacteria, and Actinobacteria were the key bacterial taxa, while Dothideomycetes, Sordariomycetes, and Eurotiomycetes were the key fungal taxa. This research provides the basis for improving the quality of cigars by improving the air-curing and fermentation processes. KEY POINTS: • Changes in POD and PPO activity control the color change of CTLs at the air-curing stage. • Monographella, Aspergillus, Pseudomonas, and Vibrio play an important role in air-curing and fermentation. • Environmental temperature and humidity mainly affect the fermentation process, whereas bacteria such as Proteobacteria, Firmicutes, Bacteroidota, and Acidobacteriota and fungi such as Ascomycota and Basidiomycota are associated with enzyme activity and temperature and humidity.

A critical assessment of the Candida strains isolated from cigar tobacco leaves

Introduction: Candida genus plays a crucial role in cigar fermentation, and strains from different sources might have differences in metabolic characteristics. Therefore, this study conducted directional isolation of Candida strains from cigar tobacco leaves and compared their fermentabilities to screen suitable strains for cigar fermentation, thereby improving the cigar quality. Methods: First, the Candida strains from cigars tobacco leaves in different production areas were directionally isolated by pure culture. Then, the isolated strains were screened based on chemical indexes and flavor component contents. Finally, the fermentabilities of preferred strains were verified by sensory evaluation. Results: Five strains of C. parapsilosis and four strains of C. metapsilosis were obtained through directional isolation. By comparing the physicochemical indexes of nine strains of Candida, it was found that C. parapsilosis P1 and C. metapsilosis M4 not only reduced the alkaloids content (by 25.3% and 32.6%, respectively) but also increased the flavor components content (by 25.2% and 18.9%, respectively). Among them, P1 could raise the content of chlorophyll degradation products, carotenoid degradation products, and Maillard reaction products, and enhance the beany and nutty flavor of cigars. M4 could raise the content of chlorophyll degradation products, cembranoids degradation products, and Maillard reaction products, and improve the baking, nutty, cocoa, and honey flavor of the cigar. Discussion: In this study, the Candida strains were directionally isolated from cigars tobacco leaves in different production areas, and two functional strains suitable for cigar fermentation were screened based on physicochemical indexes and sensory evaluation, which would contribute to the directed regulation of cigar quality and flavor diversification.

Heterogeneity changes of active bacterial community on cigar filler leaves after fermentation based on metagenome

Microorganisms play an important role in cigar fermentation. To further explore the dynamic changes of bacterial community composition, the changes of surface bacterial diversity of cigar filler leaves were investigated in the present study by high-throughput sequencing technology. It was found that the surface bacterial richness was declined after fermentation, and the dominant microorganisms on the surface of cigar filler leaves evolved from Pseudomonas spp. and Sphingomonas spp. before fermentation to Staphylococcus spp. after fermentation. The chemical composition and sensory quality evaluation of cigar filler leaves were closely related to the changes of surface bacterial community. The changes of the dominant surface bacterial community led to the differences of metabolic functions, among which the metabolic pathways such as the synthesis of secondary metabolites, carbon metabolism, and amino acid biosynthesis were significantly different. The results provide a basis for clarifying the roles of bacteria in fermentation of cigar filler leaves.

Effects of the multi-stress-resistant strain Zygosaccharomyces parabailii MC-5K3 bioaugmentation on microbial communities and metabolomics in tobacco waste extract

Industrial tobacco waste was mainly treated via a reconstituted tobacco process using the paper-making method, which involves aqueous concentrated tobacco waste extract (cTWE) fermentation (aging). The fermentation was done to improve the quality of reconstituted tobacco. However, cTWE is a multi-stress environment that is characterized by low pH (about 4), as well as high sugar (above 150 g/L) and nicotine (above 15 g/L) content. In this study, a specific selection strategy was used to successfully isolate multi-stress-resistant bacterial or fungal strains, that exhibited positive effects on cTWE fermentation, thereby improving the quality of final products. A potential strain Zygosaccharomyces parabailii MC-5K3 was used for the bioaugmentation of cTWE fermentation and it significantly influenced the microbial diversity of the fermented cTWE. Zygosaccharomyces was observed to be the only dominant fungal genus instead of some pathogenic bacterial genera, with an abundance of over 95% after four days, and still more than 80% after a week. Meanwhile, metabolomics profiling showed significant concentration decrease with regard to some flavor-improving relative metabolites, such as 3-hydroxybenzoic acid (log2FC = - 5.25) and sorbitol (log2FC = - 5.54). This finding is extrapolated to be the key influence factor on the quality of the fermented cTWE. The correlation analysis also showed that the alterations in microbial diversity in the fermented cTWE led to some important differential metabolite changes, which finally improved various properties of tobacco products.

Altered intestinal microbiota in children with bronchiolitis

Objective

To investigate the correlation between the alteration of intestinal microbiota and disease in children with bronchiolitis.

Methods

Fifty seven children diagnosed with bronchiolitis from January 2020 to January 2022 in our pediatric department were included as the case group, and another 36 normal children were included as the control group. Stool and blood were collected from both groups for high-throughput sequencing, untargeted metabolite detection and ELISA. A mouse model of RSV infection was established to validate the results of clinical case detection.

Results

Body weight, passive smoking, and a host of other factors were possible as acute bronchiolitis influencing factors in the onset of acute bronchiolitis. The alpha diversity Shannon, Simpson and Pielou's evenness indices were significantly lower in children with acute bronchiolitis than in healthy children with gated levels of Firmicutes, Bacteroidetes and genus levels of Clostridium and other short chain fatty acid-producing bacteria. The relative abundance of short-chain fatty acid (SCFAs)-producing bacteria decreased and the abundance of genus-level sphingolipid-producing bacteria Sphingomonas increased; the progression of acute bronchiolitis is likely to be associated with the abundance of Clostridium and Sphingomonas and higher fecal amino acid concentrations, including FF-MAS, L-aspartic acid, thioinosinic acid, picolinic acid; supplementation with Clostridium butyricum significantly alleviated RSV infection-induced lung inflammation.

Conclusion

The progression of bronchiolitis may be associated with altered intestinal microbiota, decreased SCFAs and elevated sphingolipids metabolism in children. Some fecal bacteria and metabolites may predict the onset of bronchiolitis, and oral administration of Clostridium butyricum may alleviate RSV infection-induced pulmonary inflammation.

Study on the effect of enzymatic treatment of tobacco on HnB cigarettes and microbial succession during fermentation

Starch and cellulose are the fundamental components of tobacco, while their excessive content will affect the quality of tobacco. Enzymatic treatment with different enzymes is a promising method to modulate the chemical composition and improve the sensory quality of tobacco leaves. In this study, enzymatic treatments, such as amylase, cellulase, and their mixed enzymes, were used to improve tobacco quality, which could alter the content of total sugar, reducing sugar, starch, and cellulose in tobacco leaves. The amylase treatment changed surface structure of tobacco leaves, increased the content of neophytadiene in tobacco by 16.48%, and improved the total smoking score of heat-not-burn (HnB) cigarette products by 5.0 points compared with the control. The Bacillus, Rubrobacter, Brevundimonas, Methylobacterium, Stenotrophomonas, Acinetobacter, Pseudosagedia-chlorotica, and Sclerophora-peronella were found to be significant biomarkers in the fermentation process by LEfSe analysis. The Basidiomycota and Agaricomycetes were significantly correlated with aroma and flavor, taste, and total score of HnB. The results showed that microbial community succession occurred due to amylase treatment, which promoted the formation of aroma compounds, and regulated the chemical composition of tobacco, and improved tobacco quality during tobacco fermentation. This study provides a method for enzymatic treatment to upgrade the quality of tobacco raw materials, thereby improving the quality of HnB cigarettes, and the potential mechanism is also revealed by chemical composition and microbial community analysis. KEY POINTS: Enzymatic treatment can change the chemical composition of tobacco leaves. The microbial community was significantly affected by enzymatic treatment. The quality of HnB cigarettes was significantly improved by amylase treatment.

Identification of Bacteria Associated with Tobacco Mildew and Tobacco-Specific Nitrosamines During Tobacco Fermentation

Tobacco mildew and tobacco-specific nitrosamines (TSNAs) affect the quality of tobacco products during fermentation. Microbes are thought to play key roles in the development of specific properties of fermented tobacco; however, little is known about the bacteria involved in the fermentation process. This study aims to identify key microbes related to mildew and TSNA formation. Tobacco was fermented at 25 °C, 35 °C, and 45 °C for 2, 4, and 6 weeks, with unfermented samples used as controls. Our preliminary exploration found that TSNAs content elevated with the increase of temperature and period, and mildew was easy to occur at low temperature with short period. Hence, samples were divided into three groups: the temperature gradient group (25 °C, 35 °C, and 45 °C for 6 weeks); the low-temperature group (control, 25 °C for 2, 4, and 6 weeks); and the high-temperature group (control, 45 °C for 2, 4, and 6 weeks). After collecting fermented tobacco leaves, 16S rRNA gene sequencing was used to explore the structure and dynamic changes of bacterial community during fermentation. Methylobacterium and Deinococcus were shared between the temperature gradient and high-temperature groups and showed a linear downward trend; these might play a role in the production of TSNAs. Massilia, Ruminiclostridium, and Cellulosilyticum species increased with prolonged fermentation time in the low-temperature group; this might be associated with tobacco mildew. In summary, the microbial diversity of fermented tobacco was explored under different conditions. These findings might provide data and material support to improve the quality of fermented tobacco products; however, further omics based studies are warranted to analysis the gene and protein expression patter in the identified bacteria.

Tobacco microbial screening and application in improving the quality of tobacco in different physical states

The first-cured tobacco contains macromolecular substances with negative impacts on tobacco products quality, and must be aged and fermented to mitigate their effects on the tobacco products quality. However, the natural fermentation takes a longer cycle with large coverage area and low economic efficiency. Microbial fermentation is a method to improve tobacco quality. The change of chemical composition of tobacco during the fermentation is often correlated with shapes of tobacco. This study aimed to investigate the effects of tobacco microorganisms on the quality of different shapes of tobacco. Specifically, Bacillus subtilis B1 and Cytobacillus oceanisediminis C4 with high protease, amylase, and cellulase were isolated from the first-cured tobacco, followed by using them for solid-state fermentation of tobacco powder (TP) and tobacco leaves (TL). Results showed that strains B1 and C4 could significantly improve the sensory quality of TP, enabling it to outperform TL in overall texture and skeleton of tobacco products during cigarette smoking. Compared with the control, microbial fermentation could increase reducing sugar; regulate protein, starch, and cellulose, reduce nicotine, improve total aroma substances, and enable the surface of fermented TP and TL to be more loose, wrinkled, and porous. Microbial community analysis indicated that strains B1 and C4 could change the native structure of microbial community in TP and TL. LEfSe analysis revealed that the potential key biomarkers in TP and TL were Bacilli, Pseudonocardia, Pantoea, and Jeotgalicoccus, which may have cooperative effects with other microbial taxa in improving tobacco quality. This study provides a theoretical basis for improving tobacco fermentation process for better cigarettes quality.

Multiomics provides insights into the succession of microbiota and metabolite during plant leaf fermentation

The quality of fermented plant products is closely related to microbial metabolism. Here, the associations of bacterial communities, metabolites, and functional genes were explored using multi-omics techniques based on plant leaf fermentation systems. The results showed significant changes in the structure of the microbial community, with a significant decrease in Firmicutes and a significant increase in Proteobacteria. In addition, the concentration of metabolites with antibacterial, antioxidant and aroma properties increased significantly, enhancing the quality of the fermented plant leaves. Integrated macrogenomic and metabolomic analyses indicated that amino acid metabolism could be key metabolic pathway affecting fermentation quality. Actinobacteria, Proteobacteria, Firmicutes were actively involved in tyrosine metabolism (ko00350) and phenylalanine metabolism (ko00360), and are presumed to be the major groups responsible for synthesizing growth and flavor compounds. This study emphasized the important role of microorganisms in the changes of metabolites during the fermentation of plant leaves.

Development of Candida autochthonous starter for cigar fermentation via dissecting the microbiome

Introduction

The main goal of tobacco fermentation technology is to minimize the alkaloid content while improving flavor substance content.

Methods

This study revealed the microbial community structure and their metabolic functions during cigar leaf fermentation by high-throughput sequencing and correlation analysis, and evaluated the fermentation performance of functional microbes based on in vitro isolation and bioaugmentation fermentation.

Results

The relative abundance of Staphylococcus and Aspergillus increased first but then decreased during the fermentation, and would occupy the dominant position of bacterial and fungal communities, respectively, on the 21st day. Correlation analysis predicted that Aspergillus, Staphylococcus and Filobasidium could contribute to the formation of saccharide compounds, Bacillus might have degradation effects on nitrogenous substances. In particular, Candida, as a co-occurring taxa and biomarker in the later stage of fermentation, could not only degrade nitrogenous substrates and synthesize flavor substances, but also contribute to maintaining the stability of microbial community. Moreover, based on in vitro isolation and bioaugmentation inoculation, it was found that Candida parapsilosis and Candida metapsilosis could significantly reduce the alkaloids content and increase the content of flavor components in tobacco leaves.

Discussion

This study found and validated the critical role of Candida in the fermentation of cigar tobacco leaves through high-throughput sequencing and bioaugmentation inoculation, which would help guide the development of microbial starters and directional regulation of cigar tobacco quality.

Application of yeast in plant-derived aroma formation from cigar filler leaves

Introduction: There are various degrees of defects of cigar filler leaves after air drying. Methods: In order to improve the quality and plant-derived aroma content of cigar filler leaves, nine aroma-producing yeasts were applied in artificially solid-state fermentation of cigar filler leaves in this study. The differences with various yeasts application were compared by chemical composition and GC-MS analysis. Results and discussion: The results showed that 120 volatile components were identified and quantified in cigar filler leaves after fermentation, including aldehydes (25 types), alcohols (24 types), ketones (20 types), esters (11 types), hydrocarbons (12 types), acids (4 types) and other substances (23 types). Based on the analysis of odor activity value (OAV), the OVA of fruity and floral aroma components were higher. It was found that floral aroma are the representative aroma types of cigar filler leaves treated with Clavispora lusitaniae, Cyberlindera fabianii, Saccharomycosis fibuligera and Zygosaccharomyces bailii R6. After being inoculated with Hanseniaspora uvarum J1, Hanseniaspora uvarum J4 and Pichia pastoris P3, the OAV of fruity aroma in cigar filler leaves was the highest, followed by tobacco aroma and woody aroma. The correlation between volatile components of cigar filler leaves with different yeasts was revealed after PCA analysis. It was concluded that the quality of cigar filler leaves was improved, and cigar filler leaves fermented with different yeasts showed different flavor.

Taxonomic and functional profiling of Indian smokeless tobacco bacteriome uncovers several bacterial-derived risks to human health

Smokeless tobacco (ST) consumption keeps human oral health at high risk which is one of the major reasons for oral tumorigenesis. The chemical constituents of the ST products have been well discussed; however, the inhabitant microbial diversity of the ST products is less explored especially from south Asian regions. Therefore, the present investigation discusses the bacteriome-based analysis of indigenous tobacco products. The study relies on 16S amplicon-based bacteriome analysis of Indian smokeless tobacco (ST) products using a metagenomic approach. A total of 59,15,143 high-quality reads were assigned to 34 phyla, 82 classes, 176 orders, 256 families, 356 genera, and 154 species using the SILVA database. Of the phyla (> 1%), Firmicutes dominate among the Indian smokeless tobacco followed by Proteobacteria, Bacteroidetes, and Actinobacteria (> 1%). Whereas, at the genera level (> 1%), Lysinibacillus, Dickeya, Terribacillus, and Bacillus dominate. The comparative analysis between the loose tobacco (LT) and commercial tobacco (CT) groups showed no significant difference at the phyla level, however, only three genera (Bacillus, Aerococcus, and Halomonas) were identified as significantly different between the groups. It indicates that CT and LT tobacco share similar bacterial diversity and poses equal health risks to human oral health. The phylogenetic investigation of communities by reconstruction of unobserved states (PICRUSt 2.0) based analysis uncovered several genes involved in nitrate/nitrite reduction, biofilm formation, and pro-inflammation that find roles in oral pathogenesis including oral cancer. The strong correlation analysis of these genes with several pathogenic bacteria suggests that tobacco products pose a high bacterial-derived risk to human health. The study paves the way to understand the bacterial diversity of Indian smokeless tobacco products and their putative functions with respect to human oral health. The study grabs attention to the bacterial diversity of the smokeless tobacco products from a country where tobacco consumers are rampantly prevalent however oral health is of least concern.

Phyllosphere microbial community of cigar tobacco and its corresponding metabolites

Cigar is made of a typical fermented tobacco where the microbiota inhabits within an alkaline environment. Our current understanding on cigar fermentation is far from thorough. This work employed both high-throughput sequencing and chromatography-mass spectrometric technologies to provide new scientific reference for this specific fermented system. Typical cigar samples from different regions (the Caribbeans, South America, East Asia, and Southeast Asia) were investigated. The results show that Firmicutes, Actinobacteria, Proteobacteria, Ascomycota, and Basidiomycota were the predominant phyla in the cigar samples. Rather than the fungal community, it was the bacterial community structures that played vital roles to differentiate the cigar from different regions: Staphylococcus was the dominant genus in the Americas; Bacillus was the dominant genus in Southeast Asia; while in East Asia, there was no dominant genus. Such differences in community structure then affected the microflora metabolism. The correlation between microbiota and metabolites revealed that Aspergillaceae, Cercospora, and Staphylococcus were significantly correlated with sclareolide; Bacillus were positively associated with isophorone. Alcaligenaceae was significantly and positively correlated with L-nicotine and hexadecanoic acid, methyl ester. GRAPHICAL ABSTRACT.

Study on the chemical compositions and microbial communities of cigar tobacco leaves fermented with exogenous additive

Fermentation process plays an important role in the biochemical properties and quality of cigar tobacco leaves (CTLs). In industry, exogenous additive (EA) was usually adopted for improving the quality of CTLs during fermentation. However, the mechanism of enhanced quality of CTLs fermented with EA was confused. Herein, the chemical compositions and microbial communities of CTLs during fermentation with EA were analyzed. The increased contents of total nitrogen and total sugar, as well as the improved consumption rate of reducing sugar in CTLs were found with the addition of EA. Besides, fermentation with EA reduced the content of total nonvolatile organic acid, especially unsaturated fatty acid. The contents of total and several representative aroma components were improved. Additionally, the increased abundance of Staphylococcus and decreased abundance of Aspergillus were detected. Combined with the changes of chemical compositions and microbial communities, it was confirmed that the carbohydrates and alcohols originated from EA promote the enrichment of Staphylococcus and accelerate biochemical reactions, such as Maillard reaction and esterification reaction, thus improving the contents and quality of aroma components in CTLs. This study demonstrated the mechanism of enhanced quality of CTLs fermented by EA, which provides more ideas for developing novel and efficient EAs.

Enzymes and microorganisms jointly promote the fermentation of rapeseed cake

Rapeseed cake is a by-product of rapeseed oil separation. The nutritional components of rapeseed cake mainly include a variety of carbohydrates, proteins, and minerals. In order to improve the conversion rate of rapeseed cake, we studied the physicochemical properties, the structure of microbial communities, and the composition of metabolites in rapeseed cake after enzymatic fermentation. The results showed that the addition of enzymatic preparation increased microbial diversity. The relative abundance of Bacillus, Lysinibacillus, Empedobacter, Debaryomyces, Hyphopichia, and Komagataella in enzymatic fermentation was significantly higher than that in natural fermentation. Unlike natural fermentation, microbial diversity during enzymatic fermentation is specific, which improves the efficiency of fermentation. Otherwise, enzymatic fermentation promotes the conversion of macromolecular substances in rapeseed cake, which increases small metabolites, such as fatty acids, organic acids, amino acids and their derivatives. The metabolite enrichment pathway is mostly concentrated in sugar metabolism and fatty acid metabolism. In conclusion, after adding enzymatic preparation, enzymes and microorganisms jointly promote the transformation of macromolecules during the fermentation of rapeseed cake, which laid a good foundation for further utilization of rapeseed cake.

Profiling the role of microorganisms in quality improvement of the aged flue-cured tobacco

Background

The aging process in the tobacco production, as in other food industries, is an important process for improving the quality of raw materials. In the spontaneous aging, the complex components in flue-cured tobacco (FT) improve flavor or reduce harmful compounds through chemical reactions, microbial metabolism, and enzymatic catalysis. Some believed that tobacco-microbe played a significant part in this process. However, little information is available on how microbes mediate chemical composition to improve the quality of FT, which will lay the foundation for the time-consuming spontaneous aging to seek ways to shorten the aging cycle.

Results

Comparing aged and unaged FT, volatile and non-volatile differential compounds (DCs) were multi-dimensionally analyzed with the non-targeted metabolomes based on UPLC-QTOP-MS (the ultra-performance liquid chromatography quadrupole time-of-flight mass spectrometry), GC–MS (gas chromatography-mass spectrometer) assisted derivatization and HP-SPME-GC/MS (headspace solid-phase micro-extraction assisted GC–MS). Products associated with the degradation pathways of terpenoids or higher fatty acids were one of the most important factors in improving FT quality. With the microbiome, the diversity and functions of microbial flora were analyzed. The high relative abundance function categories were in coincidence with DCs-related metabolic pathways. According to the correlation analysis, Acinetobacter, Sphingomonas and Aspergillus were presumed to be the important contributor, in which Aspergillus was associated with the highest number of degradation products of terpenoids and higher fatty acids. At last, the screened Aspergillus nidulans strain F4 could promote the degradation of terpenoids and higher fatty acids to enhance tobacco flavor by secreting highly active lipoxygenase and peroxidase, which verified the effect of tobacco-microbes on FT quality.

Conclusions

By integrating the microbiome and metabolome, tobacco-microbe can mediate flavor-related substances to improve the quality of FT after aging, which provided a basis for identifying functional microorganisms for reforming the traditional spontaneous aging.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-022-02597-9.

Naked-eye detection strategies coupled with isothermal nucleic acid amplification techniques for the detection of human pathogens

Nucleic acid amplification-based techniques have gained acceptance by the scientific, and general, community as reference methodologies for many different applications. Since the development of the gold standard of these techniques, polymerase chain reaction (PCR), back in the 1980s many improvements have been made, and alternative techniques emerged reporting improvements over PCR. Among these, isothermal amplification approaches resulted of particular interest as could overcome the need of specialized equipment to accurately control temperature changes, but it was after year 2000 that these techniques have flourished in a huge number of novel alternatives with many different degrees of complexities and requirements. An added value is their possibility to be combined with many different naked-eye detection strategies, simplifying the resources needed, allowing to reduce cost, and serving as the basis for novel developments of lab-on-chip systems, and miniaturized devices, for point-of-care testing. In this review, we will go over different types of naked-eye detection strategies, combined with isothermal amplification. This will provide the readers up-to-date information for them to select the most appropriate strategies depending on the particular needs and resources for their experimental setup.

Microorganisms: crucial players of smokeless tobacco for several health attributes

Global consumption of smokeless tobacco (SLT) reached 300 million users worldwide majorly from middle-income countries. More than 4000 chemical compounds represent it as one of the noxious consumable products by humans. Besides toxicants/carcinogens, the heavy microbial load on smokeless tobacco further keeps human health at higher risk. Several of these inhabitant microbes participate in biofilm formation and secrete endotoxin/mycotoxins and proinflammatory-like molecules, leading to several oral diseases. Tobacco-associated bacteria exhibit their role in tobacco-specific nitrosamines (TSNAs) formation and acetaldehyde production; both are well-documented carcinogens. Moreover, tobacco exhibits the potential to alter the oral microbiome and induce dysbiotic conditions that lead to the onset of several oral and systemic diseases. Traditional cultivation approaches of microbiology provide partial information of microbial communities of a habitat; therefore, microbiomics has now been employed to study the metagenomes of entire microbial communities. In the past 5 years, few NGS-based investigations have revealed that SLT harbors four dominant phyla (Firmicutes, Proteobacteria, Actinobacteria, and Bacteroidetes) dominating Bacillus spp. and/or Pseudomonas spp. However, functional characterization of their genetic elements will be a more informative attribute to understand the correlation between inhabitant microbial diversity and their relatedness concerning abundance and diseases. This review provides an update on the microbial diversity of SLT and its associated attributes in human health. KEY POINTS: • Heavy microbial load on smokeless tobacco alarms for poor oral hygiene. • Inhabitant microorganisms of SLT participate in TSNA and biofilm formation. • SLTs alter the oral microbiome and causes oral dysbiosis.