Microbial Fermentation Research Articles

Apple Blossom Agricultural Residues as a Sustainable Source of Bioactive Peptides through Microbial Fermentation Bioprocessing.

This study explored the impact of starter-assisted fermentation on apple blossoms to enhance their potential as a source of antioxidant and antifungal molecules. Fructobacillus fructosus PL22 and Wickerhamomyces anomalus GY1 were chosen as starters owing to their origin and promising ability to modify plant secondary metabolites. An initial assessment through microbiological and physicochemical analyses showed superior outcomes for starter-assisted fermentation compared to the spontaneous process. Enzymatic hydrolysis of proteins, primarily controlled by starters, orchestrated the generation of new low-molecular-weight peptides. W. anomalus GY1 also induced modifications in the phenolic profile, generating a diverse array of bioactive metabolites. These metabolic changes, particularly the release of potentially bioactive peptides, were associated with significant antioxidant activity and marked antifungal efficacy against three common mold species. Our results shed light on the potential of microbial starters to valorize agricultural wastes and convert them into a valuable resource for industry.

Functionalizing the Electrical Properties of Kombucha Zoogleal Mats for Biosensing Applications.

Kombucha is a type of tea that is fermented using yeast and bacteria. During this process, a film made of cellulose is produced. This film has unique properties such as biodegradability, flexibility, shape conformability, and ability to self-grow as well as be produced across customized scales. In our previous studies, we demonstrated that Kombucha mats exhibit electrical activity represented by spikes of the electrical potential. We propose using microbial fermentation as a method for in situ functionalization to modulate the electroactive nature of Kombucha cellulose mats, where graphene and zeolite were used for the functionalization. We subjected the pure and functionalized Kombucha mats to mechanical stimulation by applying different weights and geometries. Our experiments demonstrated that Kombucha mats functionalized with graphene and zeolite exhibit memfractive properties and respond to load by producing distinctive spiking patterns. Our findings present incredible opportunities for the in situ development of functionalized hybrid materials with sensing, computing, and memory capabilities. These materials can self-assemble and self-grow after they fuse their living and synthetic components. This study contributes to an emergent area of research on bioelectronic sensing and hybrid living materials, opening up exciting opportunities for use in smart wearables, diagnostics, health monitoring, and energy harvesting applications.

Relationship between dynamic changes of microorganisms in Qupi and the quality formation of Fengxiangxing Huairang Daqu.

Fengxiangxing Huairang Daqu (FHD) is one of the major types of Daqu in China. However, the relationship between the microbial community structure at different stages, the changes in the sensory characteristics, fermentation characteristics, volatiles, the most critical process point, and the quality formation of FHD is not clear. Based on microscopic characterization, PacBio SMRT sequencing, and HS-SPME-GC-MS volatile metabolite analysis revealed the relationship between FHD quality formation and the dynamics of Qupi. The results showed that the 12th day of the culture was the most critical process point, highlighting the most significant differences in microbial community structure, sensory characteristics, fermentation characteristics, and flavor substances. Bacillus licheniformis (43.25%), Saccharopolyspora rectivirgula (35.05%), Thermoascus aurantiacus (76.51%), Aspergillus amstelodami (10.81%), and Saccharomycopsis fibuligera (8.88%) were the dominant species in FHD. S. fibuligera, A. amstelodami, and T. aurantiacus were associated with the snow-white color of the FHD epidermis, the yellow color of the interior, and the gray-white color, respectively. The abundance of T. aurantiacus, A. amstelodami, B. licheniformis, and S. rectivirgula was positively associated with the esterifying power and liquefying power of FHD. The abundance of T. aurantiacus and A. amstelodami was positively correlated with the saccharifying power of FHD. The abundance of S. fibuligera was positively related to the fermenting power of FHD. A total of 248 volatiles were detected in Qupi, mainly including alcohols, esters, aldehydes, and ketones. Of them, eleven volatiles had a significant effect on the flavor of Qupi, such as 1-butanol-3-methyl-, hydrazinecarboxamide, ethanol, phenylethyl alcohol, ethyl acetate, 2-octanone, 1-octen-3-ol, formic acid-hexyl ester, (E)-2-octen-1-ol, ethyl hexanoate, and 2(3H)-furanone-dihydro-5-pentyl-. The abundance of B. licheniformis, S. rectivirgula, T. aurantiacus, and S. fibuligera was positively correlated with the alcohols, aromatic compounds, and phenols in FHD. The abundance of S. fibuligera was positively correlated with the acids, esters, and hydrocarbons in FHD. These results indicate important theoretical basis and technical support for controllable adjustment of FHD microbial community structure, stable control of FHD quality, and precise, effective, and large-scale guidance of FHD production.

Metabolic activity of gut microbial enrichment cultures from different marine species and their transformation abilities to plastic additives

The role of the gut microbiota in host physiology has been previously elucidated for some marine organisms, but little information is available on their metabolic activity involved in transformation of environmental pollutants. This study assessed the metabolic profiles of the gut microbial cultures from grouper (Epinephelus coioides), green mussel (Perna viridis) and giant tiger prawn (Penaeus monodon) and investigated their transformation mechanisms to typical plastic additives. Community-level physiological profiling analysis confirmed the utilization profiles of the microbial cultures including carbon sources of carbohydrates, amines, carboxylic acids, phenolic compounds, polymers and amino acids, and the plastic additives of organophosphate flame retardants, tetrabromobisphenol A derivates and bisphenols. Using in vitro incubation, triphenyl phosphate (TPHP) was found to be rapidly metabolized into diphenyl phosphate by the gut microbiota as a representative ester-containing plastic additive, whereas the transformation of BPA (a representative phenol) was relatively slower. Interestingly, all three kinds of microbial cultures efficiently transformed the hepatic metabolite of BPA (BPA-G) back to BPA, thereby increasing its bioavailability in the body. The specific enzyme analysis confirmed the ability of the gut microbiota to perform the metabolic reactions. The results of 16S rRNA sequencing and network analysis revealed that the genera Escherichia-Shigella, Citrobacter, and Anaerospora were functional microbes, and their collaboration with fermentative microbes played pivotal roles in the transformation of the plastic additives. The structure-specific transformations by the gut microbiota and their distinct bioavailability deserve more attention in the future.

Combinatorial metabolic engineering of Bacillus subtilis for menaquinone-7 biosynthesis.

Menaquinone-7 (MK-7), a form of vitamin K2, supports bone health and prevents arterial calcification. Microbial fermentation for MK-7 production has attracted widespread attention because of its low cost and short production cycles. However, insufficient substrate supply, unbalanced precursor synthesis, and low catalytic efficiency of key enzymes severely limited the efficiency of MK-7 synthesis. In this study, utilizing Bacillus subtilis BSAT01 (with an initial MK-7 titer of 231.0 mg/L) obtained in our previous study, the glycerol metabolism pathway was first enhanced to increase the 3-deoxy-arabino-heptulonate 7-phosphate (DHAP) supply, which led to an increase in MK-7 titer to 259.7 mg/L. Subsequently, a combination of knockout strategies predicted by the genome-scale metabolic model etiBsu1209 was employed to optimize the central carbon metabolism pathway, and the resulting strain showed an increase in MK-7 production from 259.7 to 318.3 mg/L. Finally, model predictions revealed the methylerythritol phosphate pathway as the major restriction pathway, and the pathway flux was increased by heterologous introduction (Introduction of Dxs derived from Escherichia coli) and fusion expression (End-to-end fusion of two enzymes by a linker peptide), resulting in a strain with a titer of 451.0 mg/L in a shake flask and 474.0 mg/L in a 50-L bioreactor. This study achieved efficient MK-7 synthesis in B. subtilis, laying the foundation for large-scale MK-7 bioproduction.

Pruned tea biomass plays a significant role in functional food production: A review on characterization and comprehensive utilization of abandon-plucked fresh tea leaves.

Tea is the second largest nonalcoholic beverage in the world due to its characteristic flavor and well-known functional properties in vitro and in vivo. Global tea production reaches 6.397 million tons in 2022 and continues to rise. Fresh tea leaves are mainly harvested in spring, whereas thousands of tons are discarded in summer and autumn. Herein, pruned tea biomass refers to abandon-plucked leaves being pruned in the non-plucking period, especially in summer and autumn. At present, no relevant concluding remarks have been made on this undervalued biomass. This review summarizes the seasonal differences of intrinsic metabolites and pays special attention to the most critical bioactive and flavor compounds, including polyphenols, theanine, and caffeine. Additionally, meaningful and profound methods to transform abandon-plucked fresh tea leaves into high-value products are reviewed. In summer and autumn, tea plants accumulate much more phenols than in spring, especially epigallocatechin gallate (galloyl catechin), anthocyanins (catechin derivatives), and proanthocyanidins (polymerized catechins). Vigorous carbon metabolism induced by high light intensity and temperature in summer and autumn also accumulates carbohydrates, such as soluble sugars and cellulose. The characteristics of abandon-plucked tea leaves make them not ideal raw materials for tea, but suitable for novel tea products like beverages and food ingredients using traditional or hybrid technologies such as enzymatic transformation, microbial fermentation, formula screening, and extraction, with the abundant polyphenols in summer and autumn tea serving as prominent flavor and bioactive contributors.

Valorization of lignocellulosic biomass: Progress in the production of second-generation bioethanol

Cellulosic ethanol, a biofuel product derived from microbial fermentation of cellulose-rich agricultural waste biomass, holds the potential to significantly contribute to sustainable development, energy security, and environmental friendliness as a green and renewable alternative energy source. Cellulosic ethanol offers remarkable energy benefits and carbon emission reductions. However, the biorefining process of cellulosic ethanol faces challenges and complexities. This article revolves around five aspects: feedstock, composition, pretreatment, cellulase hydrolysis, and ethanol fermentation processes in the biorefining of cellulosic ethanol. It provides an overview of the process flow and characteristics of cellulosic ethanol biorefining, emphasizing its significance. The main technological bottlenecks in cellulosic ethanol production are analyzed. Recent research advancements in cellulosic ethanol biorefining are summarized, followed by an outlook on the research focus and future prospects in the field of cellulosic ethanol.

Rational construction of a high-quality and high-efficiency biosynthetic system and fermentation optimization for A82846B based on combinatorial strategies in Amycolatopsis orientalis

BackgroundOritavancin is a new generation of semi-synthetic glycopeptide antibiotics against Gram-positive bacteria, which served as the first and only antibiotic with a single-dose therapeutic regimen to treat ABSSSI. A naturally occurring glycopeptide A82846B is the direct precursor of oritavancin. However, its application has been hampered by low yields and homologous impurities. This study established a multi-step combinatorial strategy to rationally construct a high-quality and high-efficiency biosynthesis system for A82846B and systematically optimize its fermentation process to break through the bottleneck of microbial fermentation production.ResultsFirstly, based on the genome sequencing and analysis, we deleted putative competitive pathways and constructed a better A82846B-producing strain with a cleaner metabolic background, increasing A82846B production from 92 to 174 mg/L. Subsequently, the PhiC31 integrase system was introduced based on the CRISPR-Cas12a system. Then, the fermentation level of A82846B was improved to 226 mg/L by over-expressing the pathway-specific regulator StrR via the constructed PhiC31 system. Furthermore, overexpressing glycosyl-synthesis gene evaE enhanced the production to 332 mg/L due to the great conversion of the intermediate to target product. Finally, the scale-up production of A82846B reached 725 mg/L in a 15 L fermenter under fermentation optimization, which is the highest reported yield of A82846B without the generation of homologous impurities.ConclusionUnder approaches including blocking competitive pathways, inserting site-specific recombination system, overexpressing regulator, overexpressing glycosyl-synthesis gene and optimizing fermentation process, a multi-step combinatorial strategy for the high-level production of A82846B was developed, constructing a high-producing strain AO-6. The combinatorial strategies employed here can be widely applied to improve the fermentation level of other microbial secondary metabolites, providing a reference for constructing an efficient microbial cell factory for high-value natural products.

Correlation between Microorganisms and Volatile Compounds during Spontaneous Fermentation of Sour Bamboo Shoots

Chinese sour bamboo shoot is a traditionally, spontaneous fermented food that is particularly popular due to its complex and distinctive flavor. The volatile compounds of sour bamboo shoot originate mainly from the raw materials and the microbial fermentation. To reveal the correlation between microorganisms and flavor, third-generation sequencing and Gas Chromatography-Ion Mobility Spectrometry were applied to analyze the dynamics of microbial communities at the species level and volatile compounds during sour bamboo shoot fermentation. The abundance of Lactobacillus acetotolerans and Lactobacillus fermentum increased during the fermentation, while Lactobacillus amyloliquefaciens decreased at first but then began to rise. At the end of fermentation, Lactobacillus amyloliquefaciens and Lactobacillus acetotolerans became the predominant species. A total of sixty-seven volatile compounds, which included twenty-three esters, nineteen alcohols, eight ketones, six aldehydes, six aromatic hydrocarbons, four acids and one ether, were identified. These compounds constituted the primary flavor of sour bamboo, which created a complex flavor of sour bamboo shoot. Among them, the contents of acetic acid, propionic acid, and isoamyl alcohol gradually increased during the fermentation process, and they became the main volatile compounds. Furthermore, the correlation between microorganisms and volatile compounds was investigated through two-way Orthogonal Partial Least Squares (O2PLS), which revealed a positive correlation between Lactobacillus amylolyticus and ethyl propanoate. Additionally, the abundance of Lactobacillus acetotolerans and Lactobacillus fermentum was found to be positively correlated with 2-heptenal. These findings provide a theoretical basis for understanding the formation mechanism of sour bamboo shoot flavor and the standardized production of high-quality sour bamboo shoots.

Pulsed light processing of sugarcane juice: quality evaluation and microbial load assessment.

Freshly extracted sugarcane juice is an ideal substrate for microbial fermentation and browning reactions. The present study is the first report on the potential of pulsed light (PL) processing in improving microbial stability with the retention of major bioactive. PL processing at different levels of voltage (2.1-2.7 kV) and number of pulses (100-200) was explored. The present study aimed to investigate the impact of PL processing on the quality of sugarcane juice, bioactive composition and microbial load. The microbial load, such as aerobic mesophiles, yeast and mold, and total coliform, was reduced to below 1 log colony-forming units mL-1 in juice samples subjected to intense PL treatment at 2.7 kV. The maximum value of the total color difference of the sugarcane juice was below 4.0, even at extreme levels of PL process parameters. In comparison with the unprocessed juice, the reduction in total phenols (Folin ciocalteu reagent assay) and the total antioxidant capacity (2,2-diphenyl-1-picrylhydrazyl free radical scavenging assay) was limited to 6% and 16.7%, respectively, when treated at 2.7 kV/200 pulses. The pH and total soluble solids of the juice remained unaffected in all the processed samples. Among the process parameters considered, the treatment voltage was found to significantly affect the quality parameters and microbial load. PL processing at 2.1 kV/170 pulses gave an optimally processed juice with a microbial load below the permissible limit and desirability value of 0.77. The results suggest that the PL treatment is effective for enhancing the microbial stability and maintaining the bioactive components of the sugarcane juice. Furthermore, the outcomes from the present study are expected to pave the way for further in-depth investigation of the effect of PL treatment on the critical quality attributes and shelf life of sugarcane juice. The technology will be useful for adoption by different stakeholders, including manufacturers and retailers in the food processing sector. © 2024 Society of Chemical Industry.

Advances in the synthesis of cytidine-5'-diphosphate choline

Cytidine-5'-diphosphate choline (CDP-choline) plays a crucial role in the formation of the phospholipid bilamolecular layer in cell membranes and the stabilization of the neurotransmitter system, acting as a precursor to phosphatidylcholine and acetylcholine. CDP-choline has been found effective in treating functional and consciousness disorders resulting from brain injury, Parkinson's disease, depression and glaucoma, and other conditions. As such, CDP-choline is widely utilized in clinical medicine and health care products. The conventional chemical synthesis process of CDP-choline is gradually being replaced by biosynthesis due to the expensive and toxic reagents involved, the production of various by-products, and the high cost of industrial production. Biosynthesis of CDP-choline offers two strategies: microbial fermentation and biocatalysis. Microbial fermentation utilizes inexpensive raw materials but results in a relatively low conversion rate and requires a complex separation and purification process. Biocatalysis, on the other hand, involves two stages: the growth of a living "catalyst" and the conversion of the substrate. Although the synthetic process in biocatalysis is more complex, it offers a higher conversion ratio, and the downstream processing technique for extraction is relatively less costly. Consequently, biocatalysis is currently the primary strategy for the industrial production of CDP-choline. This review aims to summarize the progress made in both chemical synthesis and biosynthesis of CDP-choline, with particular focus on the metabolic pathway and the synthetic processes involved in biocatalysis, in order to provide insights for the industrial production of CDP-choline.

Nutritional Evaluation of Milk Thistle Meal as a Protein Feedstuff for Diets of Dairy Cattle.

The objective of this work is to investigate the chemical and nutritional value of milk thistle meal (MTM) in order to improve it and to provide theoretical support for its application in dairy cattle production. MTM was assessed in comparison with seven conventional protein feed sources, namely, soybean meal (SBM), cottonseed meal (CS), canola meal (CN), palm kernel meal (PK), rice bran meal (RB), corn germ meal (CG), and sesame meal (SS). The chemical composition of these feedstuffs was assessed using wet chemical analysis, the Cornell Net Carbohydrate and Protein System was used to evaluate the carbohydrate and protein fractions, and the in situ nylon bag technique and the modified three-step in vitro method were used to assess the rumen degradation and intestinal digestibility. Additionally, Fourier transform infrared technology was used to determine the feedstuff protein spectral molecular structure and its amino acid profile was also assessed. The result showed that MTM acid detergent fiber, lignin, unavailable nitrogen, and non-degradable carbohydrate content were higher than those of the other feedstuffs. It had a 17% and 36% rumen effective degradation rate of neutral detergent fiber and dry matter, respectively, and had the lowest small intestinal rumen undegradable protein digestibility rate. It was low in leucine, histidine, arginine, and proline, but high in methionine. The total area of amide I and amide II in the protein secondary structure was similar to that of CN and CS, and the amide I and II ratio was not different from that of RB. To sum up, MTM has a poor carbohydrate composition and is high in fiber but, in comparison to most other protein feeds, has a higher crude protein rumen effective degradation rate, similar to that of SBM, and it is a good source of methionine, a limiting amino acid. Hence, its nutritional value can be further improved for application in dairy feeding through processes such as microbial or enzymatic fermentation.

Effects of Physicochemical and Biological Treatment on Structure, Functional and Prebiotic Properties of Dietary Fiber from Corn Straw.

Corn straw is one kind of agricultural by-product containing 70-80% insoluble dietary fiber (IDF). In order to develop corn straw dietary fiber, this study was conducted to increase soluble dietary fiber (SDF) yield and improve the structure, functional and prebiotic properties of IDF and SDF from corn straw treated by alkali oxidation treatment, enzymatic hydrolysis, microbial fermentation and the combination of these methods. The results demonstrated that the yield of SDF was significantly increased from 2.64% to 17.15% after corn straw was treated by alkali oxidation treatment + Aspergillus niger fermentation + cellulase hydrolysis, compared with untreated corn straw. The SDF extracted from corn straw treated by alkali oxidation treatment + Aspergillus niger fermentation + cellulase hydrolysis (F-SDF) exhibited a honeycomb structure, low crystallinity (11.97%), good antioxidant capacity and high capacities of water holding, water solubility and cholesterol absorption and promoted short-chain fatty acids production by chicken cecal microbial fermentation in vitro. F-SDF enhanced the antibacterial activity against Escherichia coli and Staphylococcus aureus proliferations of Lactobacillus plantarum when it was used as a substrate for Lactobacillus plantarum fermentation. It could be concluded that the combined treatments could increase SDF yield from corn straw and improve its functional and prebiotic properties.

Harnessing Brewery Spent Grain for Polyhydroxyalkanoate Production

The utility of brewery spent grain (BSG), a byproduct of the beer production process, for the synthesis of polyhydroxyalkanoates (PHAs), is a significant advancement towards sustainable and cost−effective biopolymer production. This paper reviews the upcycling potential of BSG as a substrate for PHA production, utilizing various biotechnological approaches to convert this abundant waste material into high−value biodegradable polymers. Through a comprehensive review of recent studies, we highlight the biochemical composition of BSG and its suitability for microbial fermentation processes. This research delves into different methodologies for PHA production from BSG, including the use of mixed microbial cultures (MMCs) for the synthesis of volatile fatty acids (VFAs), a critical precursor in PHA production, and solid−state fermentation (SSF) techniques. We also examine the optimization of process parameters such as pH, temperature, and microbial concentration through the application of the Doehlert design, revealing the intricate relationships between these factors and their impact on VFA profiles and PHA yields. Additionally, this paper discusses challenges and future perspectives for enhancing the efficiency and economic viability of PHA production from BSG. By harnessing the untapped potential of BSG, this research contributes to the development of a circular economy model, emphasizing waste valorization and the creation of sustainable alternatives to conventional plastics.

The short-chain fatty acid acetate modulates orexin/hypocretin neurons: A novel mechanism in gut-brain axis regulation of energy homeostasis and feeding

The short-chain fatty acids (SCFAs) acetate, propionate and butyrate, the major products of intestinal microbial fermentation of dietary fibres, are involved in fine-tuning brain functions via the gut-brain axis. However, the effects of SCFAs in the hypothalamic neuronal network regulating several autonomic-brain functions are still unknown. Using NMR spectroscopy, we detected a reduction in brain acetate concentrations in the hypothalamus of obese leptin knockout ob/ob mice compared to lean wild-type littermates. Therefore, we investigated the effect of acetate on orexin/hypocretin neurons (hereafter referred as OX or OX-A neurons), a subset of hypothalamic neurons regulating energy homeostasis, which we have characterized in previous studies to be over-activated by the lack of leptin and enhancement of endocannabinoid tone in the hypothalamus of ob/ob mice.We found that acetate reduces food-intake in concomitance with a reduction of orexin neuronal activity in ob/ob mice. This was demonstrated by evaluating food-intake behaviour and orexin-A/c-FOS immunoreactivity coupled with patch-clamp recordings in Hcrt-eGFP neurons, quantification of prepro-orexin mRNA, and immunolabeling of GPR-43, the main acetate receptor. Our data provide new insights into the mechanisms of the effects of chronic dietary supplementation with acetate, or complex carbohydrates, on energy intake and body weight, which may be partly mediated by inhibition of orexinergic neuron activity.

Enhanced Biosynthesis of d-Allulose from a d-Xylose-Methanol Mixture and Its Self-Inductive Detoxification by Using Antisense RNAs in Escherichia coli.

d-Allulose, a C-3 epimer of d-fructose, has great market potential in food, healthcare, and medicine due to its excellent biochemical and physiological properties. Microbial fermentation for d-allulose production is being developed, which contributes to cost savings and environmental protection. A novel metabolic pathway for the biosynthesis of d-allulose from a d-xylose-methanol mixture has shown potential for industrial application. In this study, an artificial antisense RNA (asRNA) was introduced into engineered Escherichia coli to diminish the flow of pentose phosphate (PP) pathway, while the UDP-glucose-4-epimerase (GalE) was knocked out to prevent the synthesis of byproducts. As a result, the d-allulose yield on d-xylose was increased by 35.1%. Then, we designed a d-xylose-sensitive translation control system to regulate the expression of the formaldehyde detoxification operon (FrmRAB), achieving self-inductive detoxification by cells. Finally, fed-batch fermentation was carried out to improve the productivity of the cell factory. The d-allulose titer reached 98.6 mM, with a yield of 0.615 mM/mM on d-xylose and a productivity of 0.969 mM/h.

Improving bio-conditioning dewatering performance of food waste anaerobic digestate at low ambient temperatures by heating treatment

ABSTRACT Food waste anaerobic digestate (FWAD) containing high concentrations of contaminants must be purified or recycled. Bio-conditioning dewatering followed by activated sludge process (BDAS) has emerged as a promising technology for treating FWAD. However, the bio-conditioning dewatering as a pivotal step of BDAS is often negatively affected by low ambient temperatures often occurred in winter. This study investigated the role of heating FWAD in improving the bio-conditioning dewatering performance of FWAD. Batch experiments demonstrated that the bio-conditioning dewatering efficiency increased with temperature rise. Notably, due to the low energy consumption, 50°C was considered to be the most appropriate heating treatment temperature, realizing a drastic reduction of specific resistance to filtration (SRF) of bio-conditioned FWAD from initial 1.24 × 1012 m/kg in the control at a ambient temperature of 10°C to 5.42 × 1011 m/kg and a saving of 25% in bio-conditioning reagents cost. The results of the pilot-scale and large-scale experiments revealed that heating treatment made the bio-conditioning dewatering more stable regardless of the fluctuation of ambient temperature in practical engineering. The decrease in the viscosity of bio-conditioned FWAD and the enhancement in microbial fermentation liquor flocculation capacity through heating treatment played pivotal roles in improving the bio-conditioning dewatering performance of FWAD. This work provides a cost-effective strategy to achieve efficient bio-conditioning dewatering at a relatively low ambient temperature, which was helpful in the engineering application of the novel BDAS process in wastewater treatment.

Systems metabolic engineering of Escherichia coli for high-yield production of Para-hydroxybenzoic acid

Para-hydroxybenzoic acid (PHBA) is extensively used as an additive in the food and cosmetics industries, significantly enhancing product shelf life and stability. While microbial fermentation offers an environment-friendly and sustainable method for producing PHBA, the titer and productivity are limited due to product toxicity and complex metabolic flux distributions. Here, we initially redesigned a L-phenylalanine-producing Escherichia coli by employing rational metabolic engineering strategies, resulting in the production of PHBA reached the highest reported level of 14.17 g/L. Subsequently, a novel accelerated evolution system was devised comprising deaminase, the alpha subunit of RNA polymerase, an uracil-DNA glycosylase inhibitor, and the PHBA-responsive promoter PyhcN. This system enabled us to obtain a mutant strain exhibiting a 47% increase in the half-inhibitory concentration (IC50) for PHBA within 15 days. Finally, the evolved strain achieved a production of 21.35 g/L PHBA in a 5-L fermenter, with a yield of 0.19 g/g glucose and a productivity rate of 0.44 g/L/h. This engineered strain emerges as a promising candidate for industrial production of PHBA through an eco-friendly approach.

Recent Advances in Metabolic Engineering for the Biosynthesis of Phosphoenol Pyruvate–Oxaloacetate–Pyruvate-Derived Amino Acids

The phosphoenol pyruvate–oxaloacetate–pyruvate-derived amino acids (POP-AAs) comprise native intermediates in cellular metabolism, within which the phosphoenol pyruvate–oxaloacetate–pyruvate (POP) node is the switch point among the major metabolic pathways existing in most living organisms. POP-AAs have widespread applications in the nutrition, food, and pharmaceutical industries. These amino acids have been predominantly produced in Escherichia coli and Corynebacterium glutamicum through microbial fermentation. With the rapid increase in market requirements, along with the global food shortage situation, the industrial production capacity of these two bacteria has encountered two bottlenecks: low product conversion efficiency and high cost of raw materials. Aiming to push forward the update and upgrade of engineered strains with higher yield and productivity, this paper presents a comprehensive summarization of the fundamental strategy of metabolic engineering techniques around phosphoenol pyruvate–oxaloacetate–pyruvate node for POP-AA production, including L-tryptophan, L-tyrosine, L-phenylalanine, L-valine, L-lysine, L-threonine, and L-isoleucine. Novel heterologous routes and regulation methods regarding the carbon flux redistribution in the POP node and the formation of amino acids should be taken into consideration to improve POP-AA production to approach maximum theoretical values. Furthermore, an outlook for future strategies of low-cost feedstock and energy utilization for developing amino acid overproducers is proposed.

Engineering carbon source division of labor for efficient α-carotene production in Corynebacterium glutamicum

Effective utilization of glucose, xylose, and acetate, common carbon sources in lignocellulose hydrolysate, can boost biomanufacturing economics. However, carbon leaks into biomass biosynthesis pathways instead of the intended target product remain to be optimized. This study aimed to enhance α-carotene production by optimizing glucose, xylose, and acetate utilization in a high-efficiency Corynebacterium glutamicum cell factory. Heterologous xylose pathway expression in C. glutamicum resulted in strain m4, exhibiting a two-fold increase in α-carotene production from xylose compared to glucose. Xylose utilization was found to boost the biosynthesis of pyruvate and acetyl-CoA, essential precursors for carotenoid biosynthesis. Additionally, metabolic engineering including pck, pyc, ppc, and aceE deletion, completely disrupted the metabolic connection between glycolysis and the TCA cycle, further enhancing α-carotene production. This strategic intervention directed glucose and xylose primarily towards target chemical production, while acetate supplied essential metabolites for cell growth recovery. The engineered strain C. glutamicum m8 achieved 30 mg/g α-carotene, 67% higher than strain m4. In fed-batch fermentation, strain m8 produced 1802 mg/L of α-carotene, marking the highest titer reported to date in microbial fermentation. Moreover, it exhibited excellent performance in authentic lignocellulosic hydrolysate, producing 216 mg/L α-carotene, 1.45 times higher than the initial strain (m4). These labor-division strategies significantly contribute to the development of clean processes for producing various valuable chemicals from lignocellulosic resources.