A multiple-step strategy for screening Saccharomyces cerevisiae strains with improved acid tolerance and aroma profiles

Effect of Plasma-Activated Water on the Cellulase-Producing Strain Aspergillus niger A32

To investigate the effect and mechanism of plasma-activated water (PAW) on Aspergillus niger, PAW was prepared using a needle array-plate dielectric barrier discharge plasma system. The concentrations of long-lived reactive oxygen and nitrogen species (RONS), namely, H2O2, NO2-, and NO3-, in the PAW were 48.76 mg/L, 0.046 mg/L, and 172.36 mg/L, respectively. Chemically activated water (CAW) with the same concentration of long-lived RONS was also prepared for comparison. A. niger A32 was treated with PAW and CAW. After treatment, the treated strains were observed and analyzed with scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to screen probable mutants. The results indicated that the pH, conductivity, and ORP values of PAW were 2.42, 1935 μS/cm, and 517.07 mV, respectively. In contrast, the pH and ORP values of CAW were 6.15 and 301.73 mV, respectively, which differed significantly from those of PAW. In addition, the conductivity of CAW showed no change. SEM and TEM analyses revealed that A. niger A32 treated with CAW exhibited less damage compared with the control. In contrast, A. niger A32 treated with PAW showed significant shrinkage, deformation, and exudate attachment over time. Following PAW treatment, after four passages, a high cellulase-producing stable mutant strain A-WW5 was screened, exhibiting a filter paper enzyme activity of 29.66 U/mL, a cellulose endonuclease activity of 13.79 U/mL, and a β-glucosidase activity of 27.13 U/mL. These values were found to be 33%, 38%, and 2.1% higher than those of the original fungus sample, respectively. In total, 116 SNPs and 61 InDels were present in the genome of the mutant strain A-WW5. The above findings indicate that the impact of PAW on A. niger is not only attributed to long-lasting H2O2, NO2-, and NO3- particles but also to other short-lived active particles; PAW is expected to become a new microbial breeding mutagen.

Research Progress of ARTP Mutagenesis Technology Based on Citespace Visualization Analysis

Atmospheric and room temperature plasma (ARTP) mutagenesis technology has been developed rapidly in recent years because of its simple operation, safety, environmental friendliness, high mutation rate, and large mutation library capacity. It has been widely used in traditional fields such as food, agriculture, and medicine, and has been gradually applied in emerging fields such as environmental remediation, bioenergy, and microalgae utilization. In this paper, the Web of Science Core Collection (WOSCC) was used as the data source, and the keywords and core literature of ARTP mutagenesis technology were plotted by citespace software, and the research progress and research hotspots of ARTP mutagenesis technology were analyzed. Through citespace visualization analysis, it is concluded that the country with the largest number of studies is China, the institution with the largest number of studies is Jiangnan University, and the author of the most published papers is Jiangnan University. Through keyword analysis, it is concluded that the most widely used ARTP mutagenesis technology is fermentation-related majors, mainly for biosynthesis and microbial research at the molecular level. Among them, the most widely used microorganisms are Escherichia coli and Saccharomyces cerevisiae.

Enhancing citric acid tolerance of Acetobacter tropicalis using chemical and physical mutagenesis and adaptive evolution to improve the quality of lemon fruit vinegar

The high concentration of citric acid in lemons limits the production of lemon fruit vinegar because it inhibits the metabolism of acetic acid bacteria and reduces the utilization of raw materials. This study aimed to enhance the citric acid tolerance of Acetobacter tropicalis by using complex mutagenesis and adaptive laboratory evolution (ALE) and improving the quality of lemon fruit vinegar. After mutagenesis and ALE, A. tropicalis JY-135 grew well under 40 g/L citric acid, and it showed high physiological activity and excellent fermentation performance under high concentrations of citric acid. The survival rate and ATP content of JY-135 were 15.27 and 9.30 times higher than that of the original strain J-2736. In the fermentation of lemon fruit vinegar, the acid production and the number of aroma-active compounds were 1.61-fold and 2.17-fold than J-2736. In addition, we found that citric acid tolerance of JY-135 is related to the respiratory electron-transport chain and the tricarboxylic acid (TCA) cycle. This work is of great significance for the production of high-quality lemon fruit vinegar and the enrichment of seed resources of acetic acid bacteria.

Investigation on screening, identification, and fermentation characteristics of Yunnan olive in the fermented liquid utilizing five strains of Saccharomyces cerevisiae

Refined indigenous Saccharomyces cerevisiae can enhance refinement, sophistication, and subtlety of fruit wines by showcasing exceptional regional characteristics. In order to identify exceptional indigenous S. cerevisiae strains from Yunnan olive, this study isolated 60 yeast strains from wild Yunnan olive fermentation mash. The five S. cerevisiae strains were subjected to morphological and molecular biological identification, followed by evaluation of their fermentation performance, ethanol production capacity, ester production capacity, H2S production capacity, killing capacity, and tolerance. Strains LJM-4, LJM-10, and LJM-26 exhibited robust tolerance to 6% ethanol volume fraction, pH 2.8, sucrose concentration of 400 g/L, SO2 concentration of 0.3 g/L, glucose concentration of 400 g/L at both 40 °C and 15 °C. Additionally, strain LJM-10 demonstrated a faster fermentation rate compared to the other strains. Among the tested S. cerevisiae strains evaluated in this study for olive wine fermentation process in Yunnan region; strain LJM-10 displayed superior abilities in terms of ester and ethanol production while exhibiting the lowest H2S production levels. These findings suggest that strain LJM-10 holds great potential as an excellent candidate for optimizing fruit wine S. cerevisiae fermentation processes in Yunnan olive fruit wine.

The potential for Scotch Malt Whisky flavour diversification by yeast

Scotch Whisky, a product of high importance to Scotland, has gained global approval for its distinctive qualities derived from the traditional production process, which is defined in law. However, ongoing research continuously enhances Scotch Whisky production and is fostering a diversification of flavour profiles. To be classified as Scotch Whisky, the final spirit needs to retain the aroma and taste of 'Scotch'. While each production step contributes significantly to whisky flavour-from malt preparation and mashing to fermentation, distillation, and maturation-the impact of yeast during fermentation is crucially important. Not only does the yeast convert the sugar to alcohol, it also produces important volatile compounds, e.g. esters and higher alcohols, that contribute to the final flavour profile of whisky. The yeast chosen for whisky fermentations can significantly influence whisky flavour, so the yeast strain employed is of high importance. This review explores the role of yeast in Scotch Whisky production and its influence on flavour diversification. Furthermore, an extensive examination of nonconventional yeasts employed in brewing and winemaking is undertaken to assess their potential suitability for adoption as Scotch Whisky yeast strains, followed by a review of methods for evaluating new yeast strains.

Research progress of anti-environmental factor stress mechanism and anti-stress tolerance way of Saccharomyces cerevisiae during the brewing process

Saccharomyces cerevisiae plays a decisive role in the brewing of alcohol products, and the ideal growth and fermentation characteristics can give the pure flavor of alcohol products. However, S. cerevisiae can be affected profoundly by environmental factors during the brewing process, which have negative effects on the growth and fermentation characteristics of S. cerevisiae, and seriously hindered the development of brewing industry. Therefore, we summarized the environmental stress factors (ethanol, organic acids, temperature and osmotic pressure) that affect S. cerevisiae during the brewing process. Their impact mechanisms and the metabolic adaption of S. cerevisiae in response to these stress factors. Of note, S. cerevisiae can increase the ability to resist stress factors by changing the cell membrane components, expressing transcriptional regulatory factors, activating the anti-stress metabolic pathway and enhancing ROS scavenging ability. Meantime, the strategies and methods to improve the stress- tolerant ability of S. cerevisiae during the brewing process were also introduced. Compared with the addition of exogenous anti-stress substances, mutation breeding and protoplast fusion, it appears that adaptive evolution and genetic engineering are able to generate ideal environmental stress tolerance strains of S. cerevisiae and are more in line with the needs of the current brewing industry.

Application of Atmospheric and Room-Temperature Plasma (ARTP) to Microbial Breeding

Atmospheric and room-temperature plasma (ARTP) is an efficient microbial mutagenesis method with broad application prospects. Compared to traditional methods, ARTP technology can more effectively induce DNA damage and generate stable mutant strains. It is characterized by its simplicity, cost-effectiveness, and avoidance of hazardous chemicals, presenting a vast potential for application. The ARTP technology is widely used in bacterial, fungal, and microalgal mutagenesis for increasing productivity and improving characteristics. In conclusion, ARTP technology holds significant promise in the field of microbial breeding. Through ARTP technology, we can create mutant strains with specific genetic traits and improved performance, thereby increasing yield, improving quality, and meeting market demands. The field of microbial breeding will witness further innovation and progress with continuous refinement and optimization of ARTP technology.

Recent progress in adaptive laboratory evolution of industrial microorganisms

Adaptive laboratory evolution (ALE) is a technique for the selection of strains with better phenotypes by long-term culture under a specific selection pressure or growth environment. Because ALE does not require detailed knowledge of a variety of complex and interactive metabolic networks, and only needs to simulate natural environmental conditions in the laboratory to design a selection pressure, it has the advantages of broad adaptability, strong practicability, and more convenient transformation of strains. In addition, ALE provides a powerful method for studying the evolutionary forces that change the phenotype, performance, and stability of strains, resulting in more productive industrial strains with beneficial mutations. In recent years, ALE has been widely used in the activation of specific microbial metabolic pathways and phenotypic optimization, the efficient utilization of specific substrates, the optimization of tolerance to toxic substance, and the biosynthesis of target products, which is more conducive to the production of industrial strains with excellent phenotypic characteristics. In this paper, typical examples of ALE applications in the development of industrial strains and the research progress of this technology are reviewed, followed by a discussion of its development prospects.

Achievements and perspectives of synthetic biology in botanical insecticides

Botanical insecticides are the origin of all insecticidal compounds. They have been widely used to control pests in crops for a long time. Currently, the commercial production of botanical insecticides extracted from plants is limited because of insufficient raw material supply. Synthetic biology is a promising and effective approach for addressing the current problems of the production of botanical insecticides. It is an emerging biological research hotspot in the field of botanical insecticides. However, the biosynthetic pathways of many botanical insecticides are not completely elucidated. On the other hand, the cytotoxicity of botanical pesticides and low efficiency of these biosynthetic enzymes in new hosts make it still challenging for their heterologous production. In the present review, we summarized the recent developments in the heterologous production of botanical insecticides, analyzed the current challenges, and discussed the feasible production strategies, focusing on elucidating biosynthetic pathways, enzyme engineering, host engineering, and cytotoxicity engineering. Looking to the future, synthetic biology promises to further advance heterologous production of more botanical pesticides.

Adaptive Laboratory Evolution of Yeasts for Aroma Compound Production

Aroma compounds are important in the food and beverage industry, as they contribute to the quality of fermented products. Yeasts produce several aroma compounds during fermentation. In recent decades, production of many aroma compounds by yeasts obtained through adaptive laboratory evolution has become prevalent, due to consumer demand for yeast strains in the industry. This review presents general aspects of yeast, aroma production and adaptive laboratory evolution and focuses on the recent advances of yeast strains obtained by adaptive laboratory evolution to enhance the production of aroma compounds.

Current and potential trends in the bioactive properties and health benefits of Prunus mume Sieb. Et Zucc: a comprehensive review for value maximization

Prunus mume Sieb. Et Zucc (P. mume) is an acidic fruit native to China (named Chinese Mei or greengage plum). It is currently cultivated in several Asian countries, including Japan ("Ume"), Korea (Maesil), and Vietnam (Mai or Mo). Due to its myriad nutritional and functional properties, it is accepted in different countries, and its characteristics account for its commercialization. In this review, we summarize the information on the bioactive compounds from the fruit of P. mume and their structure-activity relationships (SAR); the pulp has the highest enrichment of bioactive chemicals. The nutritional properties of P. mume and the numerous uses of its by-products make it a potential functional food. P. mume extracts exhibit antioxidant, anticancer, antimicrobial, and anti-hyperuricaemic properties, cardiovascular protective effects, and hormone regulatory properties in various in vitro and in vivo assays. SAR shows that the water solubility, molecular weight, and chemical conformation of P. mume extracts are closely related to their biological activity. However, further studies are needed to evaluate the fruit's potential nutritional and functional therapeutic mechanisms. The industrial process of large-scale production of P. mume and its extracts as functional foods or nutraceuticals needs to be further optimized.

A high‐throughput screening method for the discovery of Saccharomyces and non‐ Saccharomyces yeasts with potential in the brewing industry

Both Saccharomyces and non-Saccharomyces yeast strains are of great importance for the fermentation industry, especially with the flourishing of craft breweries, which are driving current innovations. Non-conventional yeasts can produce novel beverages with attractive characteristics such as flavour, texture, and reduced alcohol content; however, they have been poorly explored. A new method for screening the fitness of conventional and non-conventional yeast libraries utilising robotic platforms and solidified media representing industrial conditions is proposed. As proof of concept, a library formed of 6 conventional and 17 non-conventional yeast strains was distributed in 96, 384 and 1536 arrays onto a YPD agar medium. Following this, the library was replicated in different conditions mimicking beer and cider fermentation conditions. The colony size was monitored over time, and fitness values measured in maximum pixels/h and maximum biomass were calculated. Significant differences in growth were observed in between the different strains and conditions. As examples, Candida milleri Y-7245 displayed good performance in wort conditions, and Kazachstania yakushimaensis Y-48837 stood out for its performance in apple juice. The method is proposed to be used as a pre-screening step when studying vast yeast libraries. This would enable interested parties to discover potential hits for further study at a low initial cost. Furthermore, this method can be used in other applications where the desired screening media can be solidified.

Genetic Diversity for Accelerating Microbial Adaptive Laboratory Evolution

Adaptive laboratory evolution (ALE) is a widely used and highly effective tool for improving microbial phenotypes and investigating the evolutionary roots of biological phenomena. Serving as the raw materials of evolution, mutations have been extensively utilized to increase the chances of engineering molecules or microbes with tailor-made functions. The generation of genetic diversity is therefore a core technology for accelerating ALE, and a high-quality mutant library is crucial to its success. Because of its importance, technologies for generating genetic diversity have undergone rapid development in recent years. Here, we review the existing techniques for the construction of mutant libraries, briefly introduce their mechanisms and applications, discuss ongoing and emerging efforts to apply engineering technologies in the construction of mutant libraries, and suggest future perspectives for library construction.

Effects of Non-Thermal Plasma on Yeast Saccharomyces cerevisiae

Cold plasmas generated by various electrical discharges can affect cell physiology or induce cell damage that may often result in the loss of viability. Many cold plasma-based technologies have emerged in recent years that are aimed at manipulating the cells within various environments or tissues. These include inactivation of microorganisms for the purpose of sterilization, food processing, induction of seeds germination, but also the treatment of cells in the therapy. Mechanisms that underlie the plasma-cell interactions are, however, still poorly understood. Dissection of cellular pathways or structures affected by plasma using simple eukaryotic models is therefore desirable. Yeast Saccharomyces cerevisiae is a traditional model organism with unprecedented impact on our knowledge of processes in eukaryotic cells. As such, it had been also employed in studies of plasma-cell interactions. This review focuses on the effects of cold plasma on yeast cells.

Next Generation Winemakers: Genetic Engineering in Saccharomyces cerevisiae for Trendy Challenges

The most famous yeast of all, Saccharomyces cerevisiae, has been used by humankind for at least 8000 years, to produce bread, beer and wine, even without knowing about its existence. Only in the last century we have been fully aware of the amazing power of this yeast not only for ancient uses but also for biotechnology purposes. In the last decades, wine culture has become and more demanding all over the world. By applying as powerful a biotechnological tool as genetic engineering in S. cerevisiae, new horizons appear to develop fresh, improved, or modified wine characteristics, properties, flavors, fragrances or production processes, to fulfill an increasingly sophisticated market that moves around 31.4 billion € per year.

Innovative Tools and Strategies for Optimizing Yeast Cell Factories

Metabolic engineering (ME) aims to develop efficient microbial cell factories that can produce a wide variety of valuable compounds, ideally at the highest yield and from various feedstocks. We summarize recent developments in ME methods for tailoring different yeast cell factories (YCFs). In particular, we highlight the most timely and cutting-edge molecular tools and strategies for biosynthetic pathway optimization (including genome-editing tools), combinatorial transcriptional and post-transcriptional engineering (cis/trans regulators), dynamic control of metabolic fluxes (e.g., rewiring of primary metabolism), and spatial reconfiguration of metabolic pathways. Finally, we discuss challenges and perspectives for adaptive laboratory evolution (ALE) of yeast to advance ME of microbial cell factories.

Objective measures of greengage wine quality: From taste-active compound and aroma-active compound to sensory profiles

This study is sought to identify the components in greengage wine that predict the sensory properties. Taste-active compounds and aroma-active compounds of 20 commercially available greengage wines from different regions were characterized. The relationship between these compounds, wine samples and sensory attributes was modeled by partial least squares regression. The regression analysis indicated the taste-active compounds, alanine, leucine, proline, glutamic acid, lysine, malic acid, citric acid, sucrose, glucose, gallic acid, caffeic acid and tannin made a great contribution to the characteristic taste or mouthfeel of greengage wine. Meanwhile, the aroma-active compounds, including ethyl acetate, ethyl butanoate, ethyl hexanoate, ethyl octanoate, ethyl decanoate, 3-methylbutanol, 5-hydroxymethylfurfural, octanoic acid and benzaldehyde, modeled well with the flavor characteristic of greengage wine. The study revealed new insights into the relationship between chemistry and wine sensory characters, which has implications for developing an objective measurement system for determining greengage wine quality.