Designing high-performance yeast factories for the production of high-value aromatics based on a novel species and its consortia

Due to their broad applications in the field of polymers, cosmetics, nutraceuticals and pharmaceuticals, aromatic compounds have garnered multitudinous attentions. Microbial production of aromatic compounds from simple building blocks serves as a promising approach toward sustainable and scalable production of value-added chemicals. Owning to its well understood physiology, metabolism, and genetics, ease of manipulation, and capability of functionally expressing challenging endoplasmic reticulum-associated P450s, Saccharomyces cerevisiae has been overwhelmingly employed for the production of aromatic compounds, especially those plant sourced aromatic natural products with complex structures, albeit at low titers. Although numerous endeavors have been devoted to enhancing the production of aromatic compounds in S. cerevisiae, the final titers remain low and need further improvement for industrial commercialization. The insufficient production is ascribed to two aspects: one is limited precursor availability caused by tight regulations imposed on central metabolism and the other is the stepwise loss resulted from non-balanced and low throughput metabolic pathways. Looking beyond S. cerevisiae, many non-conventional yeasts possess highly desirable traits that are obtained through long term evolution in particular environment but challenging to be horizontally transferred to model hosts without compromise. However, due to the lack of the available synthetic biology elements (e. g., promoters, terminators, and vectors) and efficient genome editing method, a majority of the described non-conventional yeasts are underexploited. Unlike the model host, Scheffersomyces stipitis natively assimilates xylose that can be integrated into central metabolism exclusively through pentose phosphate pathway; thus S. stipitis has evolved highly active pentose phosphate pathway, which would be beneficial for providing the precursor, erythrose-4-phosphate, for the first committed step of the biosynthesis of aromatic compounds. Transcriptomic analysis of S. stipitis grown in various sugar-containing cultures facilitated the discovery of strong and constitutive promoters and terminators, and the identification of the rate-limiting steps in mixed-sugar utilization. The constitutive expression of genes involved in intracellular xylose metabolization together with a novel xylose-specific transporter that is free from glucose inhibition resulted in efficient simultaneous mixed-sugar utilization in S. stipitis. Further introduction of a minimal shikimate-accumulating pathway resulted in the highest shikimate titer (4.5 g/L) and yield (90.5 mg/g sugar) ever reported in yeasts. Synthetic yeast consortia were developed for the production of precursors of benzyisoquinoline alkaloids by leveraging the active upstream module from S. stipitis and the extensively optimized downstream module in S. cerevisiae. The transfer of the connecting molecule, shikimate, in the yeast consortia was empowered by two novel shikimate transporters. Through independently optimizing the two modules and tuning the cell ratio of the two specialists, the final titer of the exemplary molecule, norcoclaurine, was 160 μg/L, higher than the best titer achieved in S. cerevisiae monoculture. Future efforts should focus on ameliorating both upstream and downstream modules of the yeast consortia through genome scale engineering

Enhancing the Co-utilization of Biomass-Derived Mixed Sugars by Yeasts

Plant biomass is a promising carbon source for producing value-added chemicals, including transportation biofuels, polymer precursors, and various additives. Most engineered microbial hosts and a select group of wild-type species can metabolize mixed sugars including oligosaccharides, hexoses, and pentoses that are hydrolyzed from plant biomass. However, most of these microorganisms consume glucose preferentially to non-glucose sugars through mechanisms generally defined as carbon catabolite repression. The current lack of simultaneous mixed-sugar utilization limits achievable titers, yields, and productivities. Therefore, the development of microbial platforms capable of fermenting mixed sugars simultaneously from biomass hydrolysates is essential for economical industry-scale production, particularly for compounds with marginal profits. This review aims to summarize recent discoveries and breakthroughs in the engineering of yeast cell factories for improved mixed-sugar co-utilization based on various metabolic engineering approaches. Emphasis is placed on enhanced non-glucose utilization, discovery of novel sugar transporters free from glucose repression, native xylose-utilizing microbes, consolidated bioprocessing (CBP), improved cellulase secretion, and creation of microbial consortia for improving mixed-sugar utilization. Perspectives on the future development of biorenewables industry are provided in the end

Assessing Access to Social Services in Emerging Systems: A Conceptual Approach

There has been considerable concern about systemic factors that serve as access barriers for vulnerable groups in need of services, but conceptual and empirical work related to such issues have been limited. This article presents a new conceptual approach for considering and assessing access, which we call the “Funnel Framework”. The framework is explicated abstractly, and is illustrated with use of the U.S. child care subsidy system. We argue that the framework can usefully guide the analysis of access to any social benefit system, and can be helpful to administrators and program developers as they design and implement benefit systems

Enhancing the Co-utilization of Biomass-Derived Mixed Sugars by Yeasts

Plant biomass is a promising carbon source for producing value-added chemicals, including transportation biofuels, polymer precursors, and various additives. Most engineered microbial hosts and a select group of wild-type species can metabolize mixed sugars including oligosaccharides, hexoses, and pentoses that are hydrolyzed from plant biomass. However, most of these microorganisms consume glucose preferentially to non-glucose sugars through mechanisms generally defined as carbon catabolite repression. The current lack of simultaneous mixed-sugar utilization limits achievable titers, yields, and productivities. Therefore, the development of microbial platforms capable of fermenting mixed sugars simultaneously from biomass hydrolysates is essential for economical industry-scale production, particularly for compounds with marginal profits. This review aims to summarize recent discoveries and breakthroughs in the engineering of yeast cell factories for improved mixed-sugar co-utilization based on various metabolic engineering approaches. Emphasis is placed on enhanced non-glucose utilization, discovery of novel sugar transporters free from glucose repression, native xylose-utilizing microbes, consolidated bioprocessing (CBP), improved cellulase secretion, and creation of microbial consortia for improving mixed-sugar utilization. Perspectives on the future development of biorenewables industry are provided in the end

Building microbial factories for the production of aromatic amino acid pathway derivatives: From commodity chemicals to plant-sourced natural products

The aromatic amino acid biosynthesis pathway, together with its downstream branches, represents one of the most commercially valuable biosynthetic pathways, producing a diverse range of complex molecules with many useful bioactive properties. Aromatic compounds are crucial components for major commercial segments, from polymers to foods, nutraceuticals, and pharmaceuticals, and the demand for such products has been projected to continue to increase at national and global levels. Compared to direct plant extraction and chemical synthesis, microbial production holds promise not only for much shorter cultivation periods and robustly higher yields, but also for enabling further derivatization to improve compound efficacy by tailoring new enzymatic steps. This review summarizes the biosynthetic pathways for a large repertoire of commercially valuable products that are derived from the aromatic amino acid biosynthesis pathway, and it highlights both generic strategies and specific solutions to overcome certain unique problems to enhance the productivities of microbial hosts

Application experience of artificial perfusion combined with interception basket in ureteral calculi lithotripsy

Objective To evaluate clinical efficacy of artificial perfusion combined with interception basket in ureteral calculi lithotripsy. Methods Clinical data of 151 patients with ureteral calculi who underwent surgical treatment were retrospectively analyzed. They were divided into the observation group（artificial perfusion combined with interception basket）and control group（conventional perfusion pump）. The operation time，intraoperative blood loss，proportion of stone escape，stone re-intervention and complications were observed in two groups. Results There were no significant differences in operation time，intraoperative blood loss and incidence of complications between two groups（all P > 0.05）. The proportion of stone escape and stone re-intervention in the observation group were significantly lower than those in the control group，and the differences were statistically significant（both P < 0.05）. Conclusion Artificial low-pressure perfusion combined with interception basket in ureteral stone lithotripsy can reduce the proportion of stone escape and residual stone re-intervention and improve the stone clearance efficiency

Body Mass Index Differences in the Gut Microbiota Are Gender Specific

Background: The gut microbiota is increasingly recognized as playing an important role in the development of obesity, but the influence of gender remains elusive. Using a large cohort of Chinese adults, our study aimed to identify differences in gut microbiota as a function of body mass index (BMI) and investigate gender specific features within these differences.Methods: Five hundred fifty-one participants were categorized as underweight, normal, overweight, or obese, based on their BMI. Fecal microbiome composition was profiled via 16S rRNA gene sequencing. Generalized linear model (GLM), BugBase, PICRUSt, and SPIEC-EASI were employed to assess the variabilities in richness, diversity, structure, organism-level microbiome phenotypes, molecular functions, and ecological networks of the bacterial community that associated with BMI and sex.Results: The bacterial community of the underweight group exhibited significantly higher alpha diversity than other BMI groups. When stratified by gender, the pattern of alpha diversity across BMI was maintained in females, but no significant difference in alpha diversity was detected among the BMI groups of males. An enrichment of Fusobacteria was observed in the fecal microbiota of obese males, while obese females demonstrated an increased relative abundance of Actinobacteria. Analysis of microbial community-level phenotypes revealed that underweight males tend to have more anaerobic and less facultatively anaerobic bacteria, indicating a reduced resistance to oxidative stress. Functionally, butyrate-acetoacetate CoA-transferase was enriched in obese individuals, which might favor energy accumulation. PhoH-like ATPase was found to be increased in male obese subjects, indicating a propensity to harvest energy. The microbial ecological network of the obese group contained more antagonistic microbial interactions as well as high-degree nodes.Conclusion: Using a large Chinese cohort, we demonstrated BMI-associated differences in gut microbiota composition, functions, and ecological networks, which were influenced by gender. Results in this area have shown variability across several independent studies, suggesting that further investigation is needed to understand the role of the microbiota in modulating host energy harvest and storage, and the impact of sex on these functions

Designing high-performance yeast factories for the production of high-value aromatics based on a novel species and its consortia

Due to their broad applications in the field of polymers, cosmetics, nutraceuticals and pharmaceuticals, aromatic compounds have garnered multitudinous attentions. Microbial production of aromatic compounds from simple building blocks serves as a promising approach toward sustainable and scalable production of value-added chemicals. Owning to its well understood physiology, metabolism, and genetics, ease of manipulation, and capability of functionally expressing challenging endoplasmic reticulum-associated P450s, Saccharomyces cerevisiae has been overwhelmingly employed for the production of aromatic compounds, especially those plant sourced aromatic natural products with complex structures, albeit at low titers. Although numerous endeavors have been devoted to enhancing the production of aromatic compounds in S. cerevisiae, the final titers remain low and need further improvement for industrial commercialization. The insufficient production is ascribed to two aspects: one is limited precursor availability caused by tight regulations imposed on central metabolism and the other is the stepwise loss resulted from non-balanced and low throughput metabolic pathways. Looking beyond S. cerevisiae, many non-conventional yeasts possess highly desirable traits that are obtained through long term evolution in particular environment but challenging to be horizontally transferred to model hosts without compromise. However, due to the lack of the available synthetic biology elements (e. g., promoters, terminators, and vectors) and efficient genome editing method, a majority of the described non-conventional yeasts are underexploited. Unlike the model host, Scheffersomyces stipitis natively assimilates xylose that can be integrated into central metabolism exclusively through pentose phosphate pathway; thus S. stipitis has evolved highly active pentose phosphate pathway, which would be beneficial for providing the precursor, erythrose-4-phosphate, for the first committed step of the biosynthesis of aromatic compounds. Transcriptomic analysis of S. stipitis grown in various sugar-containing cultures facilitated the discovery of strong and constitutive promoters and terminators, and the identification of the rate-limiting steps in mixed-sugar utilization. The constitutive expression of genes involved in intracellular xylose metabolization together with a novel xylose-specific transporter that is free from glucose inhibition resulted in efficient simultaneous mixed-sugar utilization in S. stipitis. Further introduction of a minimal shikimate-accumulating pathway resulted in the highest shikimate titer (4.5 g/L) and yield (90.5 mg/g sugar) ever reported in yeasts. Synthetic yeast consortia were developed for the production of precursors of benzyisoquinoline alkaloids by leveraging the active upstream module from S. stipitis and the extensively optimized downstream module in S. cerevisiae. The transfer of the connecting molecule, shikimate, in the yeast consortia was empowered by two novel shikimate transporters. Through independently optimizing the two modules and tuning the cell ratio of the two specialists, the final titer of the exemplary molecule, norcoclaurine, was 160 μg/L, higher than the best titer achieved in S. cerevisiae monoculture. Future efforts should focus on ameliorating both upstream and downstream modules of the yeast consortia through genome scale engineering.</p