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PubMed2006

Determination of confidence intervals of metabolic fluxes estimated from stable isotope measurements.

Metabolic fluxes, estimated from stable isotope studies, provide a key to quantifying physiology in fields ranging from metabolic engineering to the analysis of human metabolic diseases. A serious drawback of the flux estimation method in current use is that it does not produce confidence limits for the estimated fluxes. Without this information it is difficult to interpret flux results and expand the physiological significance of flux studies. To address this shortcoming we derived analytical expressions of flux sensitivities with respect to isotope measurements and measurement errors. These tools allow the determination of local statistical properties of fluxes and relative importance of measurements. Furthermore, we developed an efficient algorithm to determine accurate flux confidence intervals and demonstrated that confidence intervals obtained with this method closely approximate true flux uncertainty. In contrast, confidence intervals approximated from local estimates of standard deviations are inappropriate due to inherent system nonlinearities. We applied these methods to analyze the statistical significance and confidence of estimated gluconeogenesis fluxes from human studies with [U-13C]glucose as tracer and found true limits for flux estimation in specific human isotopic protocols.

Blood Glucose↗

PubMed2001

Understanding the art of producing protein and nonprotein molecules in Escherichia coli.

The high-level production of functional proteins in E. coli is a very extense field of research in biotechnology. A number of important aspects to be considered in the initial design of an expression system and their interplay, were clear years ago. However, in recent times, strategies that go beyond transcription, translation, stability, vector, and strain choice, have been developed; so now expression of active peptides can be viewed as a more integrated process. Coexpression of protein subunits, foldases and chaperones, protein folding, location and purification schemes, metabolic engineering of the cell's central metabolism, and in vitro refolding strategies, are some of the novelties that are now available to aid in the success of an efficient expression system for active heterologous proteins. This review presents a compilation of the basic issues that influence the success in the production of protein and nonprotein products in Escherichia coli, as well as some general strategies designed to facilitate downstream process operations and improve biosynthesis yields.

Escherichia coli↗

PubMed1997

Fermentation of biomass-derived glucuronic acid by pet expressing recombinants of E. coli B.

The economics of large-scale production of fuel ethanol from biomass and wastes requires the efficient utilization of all the sugars derived from the hydrolysis of the heteropolymeric hemicellulose component of lignocellulosic feedstocks. Glucuronic and 4-O-methyl-glucuronic acids are major side chains in xylans of the grasses and hardwoods that have been targeted as potential feedstocks for the production of cellulosic ethanol. The amount of these acids is similar to that of arabinose, which is now being viewed as another potential substrate in the production of biomass-derived ethanol. This study compared the end-product distribution associated with the fermentation of D-glucose (Glc) and D-glucuronic acid (GlcUA) (as sole carbon and energy sources) by Escherichia coli B (ATCC 11303) and two different ethanologenic recombinants--a strain in which pet expression was via a multicopy plasmid (pLOI297) and a chromosomally integrated construct, strain KO11. pH-stat batch fermentations were conducted using a modified LB medium with 2% (w/v) Glc or GlcUA with the set-point for pH control at either 6.3 or 7.0. The nontransformed host culture produced only lactic acid from glucose, but fermentation of GlcUA yielded a mixture of ethanol, acetic, and lactic acids, with acetic acid being the predominant end-product. The ethanol yield associated with GlcUA fermentation by both recombinants was similar, but acetic acid was a significant by-product. Increasing the pH from 6.3 to 7.0 increased the rate of glucuronate fermentation, but it also decreased the ethanol mass yield from 0.22 to 0.19 g/g primarily because of an increase in acetic acid production. In all fermentations there was good closure of the carbon mass balance, the exception being the recombinant bearing plasmid pLOI297 that produced an unidentified product from GlcUA. The metabolism of GlcUA by this metabolically engineered construct remains unresolved. The results offered insights into metabolic fluxes and the regulation of pyruvate catabolism in the wild-type and engineered strains. End-product distribution for metabolism of glucuronic acid by the nontransformed, wild-type E. coli B and recombinant strain KO11 suggests that the enzyme pyruvate-formate lyase is not solely responsible for the production of acetylCoA from pyruvate and that derepressed pyruvate dehydrogenase may play a significant role in the metabolism of GlcUA.

Acetyltransferases↗

PubMed2026

Genomic features, metabolism, and biotechnological applications of Candida tropicalis and other non-albicans Candida species.

The production of bio-based products by yeasts from agroindustrial byproducts is a key strategy for advancing circular bioeconomy. While Saccharomyces species remain the predominant industrial yeasts, their limited ability to assimilate lactose, pentoses, and glycerol, as well as their sensitivity to lignocellulose-derived inhibitors, restricts their efficient application in bioprocesses based on using industrial byproducts as fermentation media. In contrast, several non-albicans Candida species exhibit broad substrate utilization capacities and enhanced tolerance to industrial stresses, making them attractive candidates for the bioconversion of agroindustrial residues. This review critically examines recent advances in the genomic, metabolic, and physiological characterization of promising non-albicans Candida species, including Candida tropicalis, Candida parapsilosis, Candida viswanathii, Candida sojae, and Candida maltosa. Emphasis is given to genome-scale metabolic models, carbon assimilation pathways, stress-response mechanisms, and metabolic engineering approaches aiming at the production of value-added compounds. By identifying current achievements, knowledge gaps, and biotechnological bottlenecks, this review highlights the potential of these yeasts as emerging platforms for sustainable bioprocesses within a circular bioeconomy framework.

Biotechnology↗

PubMed2004

Engineering precursor flow for increased erythromycin production in Aeromicrobium erythreum.

Metabolic engineering technology for industrial microorganisms is under development to create rational, more reliable, and more cost-effective approaches to strain improvement. Strain improvement is a critical component of the drug development process, yet the genetic basis for high production by industrial microorganisms is still a mystery. In this study, a search was begun for genetic modifications critical for high-level antibiotic production. The model system used was erythromycin production studied in the unicellular actinomycete, Aeromicrobium erythreum. A tagged-mutagenesis approach allowed reverse engineering of improved strains, revealing two genes, mutB and cobA, in the primary metabolic branch for methylmalonyl-CoA utilization. Knockouts in these genes created a permanent metabolic switch in the flow of methylmalonyl-CoA, from the primary branch into a secondary metabolic branch, driving erythromycin overproduction. The model provides insights into the regulation and evolution of secondary metabolism.

Actinobacteria↗

PubMed2006

The production of polyhydroxyalkanoates in recombinant Escherichia coli.

Polyhydroxyalkanoates, the natural polyester that many microorganisms accumulate to store carbon and reducing equivalents, have been considered as a future alternative of traditional plastic due to their special properties. In Escherichia coli, a previous non-polyhydroxyalkanoates producer, pathway engineering has been developed as a very powerful approach to set up microbial production process through the introduction of direct genetic changes by recombinant DNA technology. Various metabolic pathways leading to the polyhydroxyalkanoates accumulation with desirable properties at low-cost and high-productivity have been developed. At the same time, high density fermentation technology of E. coli provides an efficient polyhydroxyalkanoates production strategy. This review focused on metabolic engineering, fermentation and downstream process aiming to polyhydroxyalkanoates production in E. coli.

Escherichia coli↗

PubMed2006

Computational tools for isotopically instationary 13C labeling experiments under metabolic steady state conditions.

(13)C metabolic flux analysis (MFA) has become an important and powerful tool for the quantitative analysis of metabolic networks in the framework of metabolic engineering. Isotopically instationary (13)C MFA under metabolic stationary conditions is a promising refinement of classical stationary MFA. It accounts for the experimental requirements of non-steady-state cultures as well as for the shortening of the experimental duration. This contribution extends all computational methods developed for classical stationary (13)C MFA to the instationary situation by using high-performance computing methods. The developed tools allow for the simulation of instationary carbon labeling experiments (CLEs), sensitivity calculation with respect to unknown parameters, fitting of the model to the measured data, statistical identifiability analysis and an optimal experimental design facility. To explore the potential of the new approach all these tools are applied to the central metabolism of Escherichia coli. The achieved results are compared to the outcome of the stationary counterpart, especially focusing on statistical properties. This demonstrates the specific strengths of the instationary method. A new ranking method is proposed making both an a priori and an a posteriori design of the sampling times available. It will be shown that although still not all fluxes are identifiable, the quality of flux estimates can be strongly improved in the instationary case. Moreover, statements about the size of some immeasurable pool sizes can be made.

Biomedical Engineering↗

PubMed2026

Enhancing phytosterol tolerance and Repeated-Batch androstenedione production in Mycolicibacterium by modulating global acylation levels.

Global protein lysine acylation, driven by intracellular acyl-coenzyme A (acyl-CoA) accumulation during phytosterol catabolism, has emerged as a potential regulatory mechanism in steroid biotransformation, yet its role in androstenedione (AD) production by Mycolicibacterium remains unexplored. Here, we identified and functionally characterized two antagonistic enzymes in Mycobacterium sp. LZ2 (Msp): MpKat, a GNAT-family acyltransferase catalyzing lysine succinylation, and MpSir, an NAD+-dependent Sirtuin-family deacylase. Genome-wide prediction indicated that 21.56% of lysine residues in the Msp proteome are potential acylation sites, underscoring the broad regulatory impact of this modification. Targeted genetic manipulation revealed that MpSir overexpression increased AD yield by 13.28% (to 83.24%), and MpKat knockout improved yield by 8.86%, while MpKat overexpression decreased yield by 8.69%. Reducing global acylation levels alleviated oxidative stress, elevated NAD+/NADH ratios, enhanced phytosterol tolerance, and improved cell viability. In repeated-batch fermentation, the MpSir-overexpressing strain achieved an average AD yield of 76.5% with a 51% reduction in fermentation time compared to the wild type. This work demonstrates for the first time that modulation of protein acylation via the MpKat/MpSir regulatory axis is a viable and effective strategy to enhance steroid bioconversion in mycobacteria, offering a new dimension for metabolic engineering beyond conventional pathway optimization.

Androstenedione↗

PubMed2006

Design, construction and performance of the most efficient biomass producing E. coli bacterium.

Inverse metabolic engineering based on elementary mode analysis was applied to maximize the biomass yield of Escherchia coli MG1655. Elementary mode analysis was previously employed to identify among 1691 possible pathways for cell growth the most efficient pathway with maximum biomass yield. The metabolic network analysis predicted that deletion of only 6 genes reduces the number of possible elementary modes to the most efficient pathway. We have constructed a strain containing these gene deletions and we evaluated its properties in batch and in chemostat growth experiments. The results show that the theoretical predictions are closely matched by the properties of the designed strain.

Biomass↗

PubMed2026

Integrated proteomic and acetylomic analyses reveal the metabolic reprogramming associated with increased tylosin-equivalent concentration in Streptomyces xinghaiensis sf106-B1.

Deciphering the metabolic basis of high-yield antibiotic production in Streptomyces is crucial for strain optimization. Atmospheric and room-temperature plasma (ARTP) mutagenesis of Streptomyces xinghaiensis sf106 generated a mutant with a 30% increase in tylosin-equivalent concentration (μg/mL). 4D-FastDIA quantitative proteomics identified 279 differentially abundant proteins enriched in the Type I polyketide synthase (PKS) pathway, with increased abundance of key macrolide-biosynthesis-related proteins. Lysine-acetylome profiling identified 1152 differentially abundant acetylation sites and revealed altered acetylation of enzymes involved in fatty acid metabolism and the tricarboxylic acid (TCA) cycle, suggesting adjustments in central metabolism associated with acyl-CoA precursor availability and energy generation. Integration of proteomic and acetylomic data suggests coordinated changes in protein abundance and lysine acetylation associated with the increased tylosin-equivalent concentration. These results highlight candidate nodes for rational metabolic engineering of S. xinghaiensis.

Streptomyces↗

PubMed2004

Clostridium cellulolyticum: model organism of mesophilic cellulolytic clostridia.

Clostridium cellulolyticum ATCC 35319 is a non-ruminal mesophilic cellulolytic bacterium originally isolated from decayed grass. As with most truly cellulolytic clostridia, C. cellulolyticum possesses an extracellular multi-enzymatic complex, the cellulosome. The catalytic components of the cellulosome release soluble cello-oligosaccharides from cellulose providing the primary carbon substrates to support bacterial growth. As most cellulolytic bacteria, C. cellulolyticum was initially characterised by limited carbon consumption and subsequent limited growth in comparison to other saccharolytic clostridia. The first metabolic studies performed in batch cultures suggested nutrient(s) limitation and/or by-product(s) inhibition as the reasons for this limited growth. In most recent investigations using chemostat cultures, metabolic flux analysis suggests a self-intoxication of bacterial metabolism resulting from an inefficiently regulated carbon flow. The investigation of C. cellulolyticum physiology with cellobiose, as a model of soluble cellodextrin, and with pure cellulose, as a carbon source more closely related to lignocellulosic compounds, strengthen the idea of a bacterium particularly well adapted, and even restricted, to a cellulolytic lifestyle. The metabolic flux analysis from continuous cultures revealed that (i) in comparison to cellobiose, the cellulose hydrolysis by the cellulosome introduces an extra regulation of entering carbon flow resulting in globally lower metabolic fluxes on cellulose than on cellobiose, (ii) the glucose 1-phosphate/glucose 6-phosphate branch point controls the carbon flow directed towards glycolysis and dissipates carbon excess towards the formation of cellodextrins, glycogen and exopolysaccharides, (iii) the pyruvate/acetyl-CoA metabolic node is essential to the regulation of electronic and energetic fluxes. This in-depth analysis of C. cellulolyticum metabolism has permitted the first attempt to engineer metabolically a cellulolytic microorganism.

Biodegradation, Environmental↗

PubMed2002

Metabolomics: quantification of intracellular metabolite dynamics.

The rational improvement of microbial strains for the production of primary and secondary metabolites ('metabolic engineering') requires a quantitative understanding of microbial metabolism. A process by which this information can be derived from dynamic fermentation experiments is presented. By applying a substrate pulse to a substrate-limited, steady state culture, cellular metabolism is shifted away from its metabolic steady state. With the aid of a rapid sampling and quenching routine it is possible to take 4-5 samples per second during this process, thus capturing the metabolic response to this stimulus. Over 30 metabolites, nucleotides and cofactors from Escherichia coli metabolism can be extracted and analysed using a range of different techniques, for example enzymatic assays, HPLC and LC-MS methods. Using different substrates as limiting and pulse-substrates (glucose, glycerol), different metabolic pathways and substrate uptake systems are investigated. The resulting plots of intracellular metabolite concentrations against time serve as a data basis for modelling microbial metabolic networks.

Bioreactors↗

PubMed2004

Metabolic control analysis under uncertainty: framework development and case studies.

Information about the enzyme kinetics in a metabolic network will enable understanding of the function of the network and quantitative prediction of the network responses to genetic and environmental perturbations. Despite recent advances in experimental techniques, such information is limited and existing experimental data show extensive variation and they are based on in vitro experiments. In this article, we present a computational framework based on the well-established (log)linear formalism of metabolic control analysis. The framework employs a Monte Carlo sampling procedure to simulate the uncertainty in the kinetic data and applies statistical tools for the identification of the rate-limiting steps in metabolic networks. We applied the proposed framework to a branched biosynthetic pathway and the yeast glycolysis pathway. Analysis of the results allowed us to interpret and predict the responses of metabolic networks to genetic and environmental changes, and to gain insights on how uncertainty in the kinetic mechanisms and kinetic parameters propagate into the uncertainty in predicting network responses. Some of the practical applications of the proposed approach include the identification of drug targets for metabolic diseases and the guidance for design strategies in metabolic engineering for the purposeful manipulation of the metabolism of industrial organisms.

Algorithms↗

PubMed2006

Biosynthesis and engineering of isoprenoid small molecules.

Isoprenoid secondary metabolites are a rich source of commercial products that have not been fully explored. At present, there are isoprenoid products used in cancer therapy, the treatment of infectious diseases, and crop protection. All isoprenoids share universal prenyl diphosphate precursors synthesized via two distinct pathways. From these universal precursors, the biosynthetic pathways to specific isoprenoids diverge resulting in a staggering array of products. Taking advantage of this diversity has been the focus of much effort in metabolic engineering heterologous hosts. In addition, the engineering of the mevalonate pathway has increased levels of the universal precursors available for heterologous production. Finally, we will describe the efforts to produce to commercial terpenoids, paclitaxel and artemisinin.

Artemisinins↗

PubMed2026

Genome-scale overexpression screening identifies product tolerance and efflux transport as key determinants of high-level L-tryptophan production in Escherichia coli.

L-tryptophan is a high-value aromatic amino acid widely used in the food, feed, and pharmaceutical industries. However, large-scale microbial production is constrained by insufficient precursor supply and limited strain tolerance to high product concentrations. In this study, modular metabolic engineering was first employed to enhance the availability of key precursors, including shikimate, serine, and glutamine, yielding strain TRPJ-13 with a 34.6% increase in L-tryptophan titer. To enhance strain tolerance, an indigo-based high-throughput reporter system was constructed and coupled with genome-scale overexpression library screening, leading to the identification of soxS as a tolerance-conferring target. Mechanistic analysis demonstrated that soxS upregulated lpxC to enhance lipopolysaccharide biosynthesis, thereby reinforcing membrane integrity and improving L-tryptophan tolerance. Combinatorial engineering of soxS and lpxC generated strain TRPJ-23, which increased L-tryptophan tolerance by 74.8% and L-tryptophan titer by 10.3%. Furthermore, YicL was identified as a novel transmembrane protein involved in L-tryptophan transport that effectively promoted L-tryptophan efflux, further increasing the titer by 9.0%. After fermentation optimization, strain TRPJ-28 produced 74.3 g/L L-tryptophan in a 5-L bioreactor, with a yield of 0.26 g/g and a productivity of 1.24 g/L/h. In a 1000-L pilot-scale bioreactor, TRPJ-28 reached a titer, yield, and productivity of 70.4 g/L, 0.25 g/g, and 1.17 g/L/h, respectively. This study provides new engineering insights for developing industrially promising L-tryptophan-producing strains.

Genome-scale overexpression screening↗

PubMed2026

Kinetic model of a determinate legume root nodule reveals plant metabolic characteristics for more efficient nitrogen fixation symbiosis.

While nitrogen fertilizers are widely used in agricultural production, their application incurs significant environmental and energetic costs. In contrast, some crops are less dependent on these fertilizers because they engage in symbioses with rhizobia, nitrogen-fixing bacteria that provide ammonium to the plant in exchange for carbon. However, the carbon cost associated with nitrogen fixation can negatively impact crop yields. Improving the efficiency of this metabolic process could alleviate this impact on crop productivity. Mathematical models can help us quantitatively explore metabolic behavior and identify potential targets for metabolic engineering. In this work, we developed a kinetic model of determinate root nodule metabolism, where this symbiotic exchange of carbon from the plant and nitrogen from the bacteria occurs. We used this model to evaluate how the predicted metabolic behavior differs between inefficient and efficient nodules, and to identify potential engineering targets for improving nitrogen fixation efficiency and rate. We show that the enzymes phosphoenolpyruvate carboxylase and pyruvate kinase have significant influence on the predicted rate and efficiency of nitrogen fixation, especially when their expression is varied in combination with oxidative Pentose Phosphate Pathway enzymes like glucose-6-phosphate dehydrogenase and 6-phosphogluconolactonase. The model predicts that pairing a 3-fold decrease in glucose-6-phosphate dehydrogenase activity along with either a 3-fold increase in phosphoenolpyruvate carboxylase activity or decrease in pyruvate kinase activity could increase nitrogen fixation rate by 8.82% while improving nitrogen fixation efficiency by 10.99%.

Enzyme kinetics↗

PubMed2002

Wine yeast strains engineered for glycogen overproduction display enhanced viability under glucose deprivation conditions.

We used metabolic engineering to produce wine yeasts with enhanced resistance to glucose deprivation conditions. Glycogen metabolism was genetically modified to overproduce glycogen by increasing the glycogen synthase activity and eliminating glycogen phosphorylase activity. All of the modified strains had a higher glycogen content at the stationary phase, but accumulation was still regulated during growth. Strains lacking GPH1, which encodes glycogen phosphorylase, are unable to mobilize glycogen. Enhanced viability under glucose deprivation conditions occurs when glycogen accumulates in the strain that overexpresses GSY2, which encodes glycogen synthase and maintains normal glycogen phosphorylase activity. This enhanced viability is observed under laboratory growth conditions and under vinification conditions in synthetic and natural musts. Wines obtained from this modified strain and from the parental wild-type strain don't differ significantly in the analyzed enological parameters. The engineered strain might better resist some stages of nutrient depletion during industrial use.

Culture Media↗

PubMed2026

Microbial decaprenoxanthin: From understanding an extremophile-derived C50 carotenoid to its bioprocessing for large-scale applications.

Decaprenoxanthin (DPXT) is an unusual bacterial C50 carotenoid that has historically received limited attention despite its well-defined structure. For decades, carotenoid research and industrial development have been dominated by C40 carotenoids, leaving longer-chain carotenoids largely overlooked. Recent discoveries, particularly from microorganisms inhabiting Antarctic and other extreme environments, have repositioned DPXT as an adaptive pigment shaped by intense environmental pressures. Its extended polyene chain and membrane-associated behavior suggest roles in membrane stabilization and protection against ultraviolet radiation and oxidative stress, features that may hold relevance for food and biotechnological applications. This review integrates historical and recent knowledge on DPXT, covering its structural characteristics, biosynthetic pathways, ecological function, and emerging technological relevance. Special attention is given to microbial sources, particularly Actinomycetota from extreme environments, and to recent advances in microbial genomics, metabolic engineering, and sustainable bioprocess development that enable the production and exploration of C50 carotenoids beyond their native extremophilic context. The analysis highlights DPXT as a representative example of stress-resilient carotenoids, with physicochemical and membrane-interacting properties that may offer advantages for future food and biotechnological systems. Although significant challenges remain in cultivation strategies, yield optimization, and downstream recovery, advances in microbial cell factories and green extraction technologies open new opportunities for valorizing C50 carotenoids. This review bridges extremophile microbiology, carotenoid biochemistry, and sustainable food innovation, positioning DPXT as an emerging molecule that may expand the functional and structural landscape of carotenoids relevant to food science.

Carotenoids↗