Intracellular Metabolite Pool Changes in Response to Nutrient Depletion Induced Metabolic Switching in Streptomyces coelicolor

Phosphonoalamides Reveal the Biosynthetic Origin of Phosphonoalanine Natural Products and a Convergent Pathway for Their Diversification

Phosphonate natural products, with their potent inhibitory activity, have found widespread use across multiple industries. Their success has inspired development of genome mining approaches that continue to reveal previously unknown bioactive scaffolds and biosynthetic insights. However, a greater understanding of phosphonate metabolism is required to enable prediction of compounds and their bioactivities from sequence information alone. Here, we expand our knowledge of this natural product class by reporting the complete biosynthesis of the phosphonoalamides, antimicrobial tripeptides with a conserved N-terminal l-phosphonoalanine (PnAla) residue produced by Streptomyces. The phosphonoalamides result from the convergence of PnAla biosynthesis and peptide ligation pathways. We elucidate the biochemistry underlying the transamination of phosphonopyruvate to PnAla, a new early branchpoint in phosphonate biosynthesis catalyzed by an aminotransferase with evolved specificity for phosphonate metabolism. Peptide formation is catalyzed by two ATP-grasp ligases, the first of which produces dipeptides, and a second which ligates dipeptides to PnAla to produce phosphonoalamides. Substrate specificity profiling revealed a dramatic expansion of dipeptide and tripeptide products, while finding PnaC to be the most promiscuous dipeptide ligase reported thus far. Our findings highlight previously unknown transformations in natural product biosynthesis, promising enzyme biocatalysts, and unveil insights into the diversity of phosphonopeptide natural products.

Role of Carbon, Nitrogen, Phosphate and Sulfur Metabolism in Secondary Metabolism Precursor Supply in Streptomyces spp

The natural soil environment of Streptomyces is characterized by variations in the availability of nitrogen, carbon, phosphate and sulfur, leading to complex primary and secondary metabolisms. Their remarkable ability to adapt to fluctuating nutrient conditions is possible through the utilization of a large amount of substrates by diverse intracellular and extracellular enzymes. Thus, Streptomyces fulfill an important ecological role in soil environments, metabolizing the remains of other organisms. In order to survive under changing conditions in their natural habitats, they have the possibility to fall back on specialized enzymes to utilize diverse nutrients and supply compounds from primary metabolism as precursors for secondary metabolite production. We aimed to summarize the knowledge on the C-, N-, P- and S-metabolisms in the genus Streptomyces as a source of building blocks for the production of antibiotics and other relevant compounds.

Adaptive Laboratory Evolution of Probiotics toward Oxidative Stress Using a Microfluidic-Based Platform

Adaptive laboratory evolution (ALE) can be used to make bacteria less susceptible to oxidative stress. An alternative to large batch scale ALE cultures is to use microfluidic platforms, which are often more economical and more efficient. Microfluidic ALE platforms have shown promise, but many have suffered from subpar cell passaging mechanisms and poor spatial definition. A new approach is presented using a microfluidic Evolution on a Chip (EVoc) design which progressively drives microbial cells from areas of lower H2O2 concentration to areas of higher concentration. Prolonged exposure, up to 72 h, revealed the survival of adaptive strains of Lacticaseibacillus rhamnosus GG, a beneficial probiotic often included in food products. After performing ALE on this microfluidic platform, the bacteria persisted under high H2O2 concentrations in repeated trials. After two progressive exposures, the ability of L. rhamnosus to grow in the presence of H2O2 increased from 1 mm H2O2 after a lag time of 31 h to 1 mm after 21 h, 2 mm after 28 h, and 3 mm after 42 h. The adaptive strains have different morphology, and gene expression compared to wild type, and genome sequencing revealed a potentially meaningful single nucleotide mutation in the protein omega-amidase.

Optimized submerged batch fermentation for metabolic switching in Streptomyces yanglinensis 3-10 providing platform for reveromycin A and B biosynthesis, engineering, and production

The cultivation system requires that the approach providing biomass for all types of metabolic analysis is of excellent quality and reliability. This study was conducted to enhance the efficiency and yield of antifungal substance (AFS) production in Streptomyces yanglinensis 3-10 by optimizing operation conditions of aeration, agitation, carbon source, and incubation time in a fermenter. Dissolved oxygen (DO) and pH were found to play significant roles in AFS production. The optimum pH for the production of AFS in S. yanglinensis 3-10 was found to be 6.5. As the AFS synthesis is generally thought to be an aerobic process, DO plays a significant role. The synthesis of bioactive compounds can vary depending on how DO affects growth rate. This study validates that the high growth rate and antifungal activity required a minimum DO concentration of approximately 20% saturation. The DO supply in a fermenter can be raised once agitation and aeration have been adjusted. Consequently, DO can stimulate the development of bacteria and enzyme production. A large shearing effect could result from the extreme agitation, harming the cell and deactivating its products. The highest inhibition zone diameter (IZD) was obtained with 3% starch, making starch a more efficient carbon source than glucose. Temperature is another important factor affecting AFS production. The needed fermentation time would increase and AFS production would be reduced by the too-low operating temperature. Furthermore, large-scale fermenters are challenging to manage at temperatures that are far below from room temperature. According to this research, 28°C is the ideal temperature for the fermentation of S. yanglinensis 3-10. The current study deals with the optimization of submerged batch fermentation involving the modification of operation conditions to effectively enhance the efficiency and yield of AFS production in S. yanglinensis 3-10.

Nutrient-depended metabolic switching during batch cultivation of Streptomyces coelicolor explored with absolute quantitative mass spectrometry-based metabolite profiling

The well-known secondary metabolite-producing bacterium Streptomyces coelicolor is a natural choice for the development of super-hosts optimized for the heterologous expression of antibiotic biosynthetic gene clusters (BGCs). In this study, we used S. coelicolor M145 and its derivative strain M1146 where all active BGCs have been deleted and generated high-resolution quantitative time series metabolite profiles under two cultivation conditions (phosphate and nitrogen limitation to cease growth and trigger secondary metabolism). Five targeted LC-MS/MS-based methods were used to quantify intracellular primary metabolites covering phosphorylated metabolites, amino acids, organic acids, (deoxy) nucleoside/sugar phosphates, Nicotinamide adenine dinucleotide (NAD), and Coenzyme A (CoA). The nitrogen limitation resulted in a sharp decline in respiration and an immediate drop in the cell mass concentration. Intracellularly, a reduction in the level of the metabolites next to α-ketoglutarate in the tricarboxylic acid cycle and a decrease in the NADH pool were among the most prominent adaptation to this nutrient limitation. Phosphate limitation evoked a different adaptation of the metabolite pools as most of the phosphorylated metabolite pools except 6-phosphogluconic acid (6PG) pool were downregulated. ¹³C-isotope-labeling experiments revealed the simultaneous activity of both glycolysis and gluconeogenesis during the co-utilization of glucose and glutamate. The S. coelicolor M1146 strain had similar time-series metabolite profile dynamics as the parent M145 strain, except for a visibly increased 6PG pool in the stationary phase. In general, the nutrient limitation had a larger effect on the metabolite pool levels than the absence of secondary metabolite production in M1146. This study provides new insight into the primary carbon metabolism and its link to the secondary metabolism which is needed for further optimization of both super-host genotype and cultivation conditions.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-022-03146-x.

Artificial Consortium of Three E. coli BL21 Strains with Synergistic Functional Modules for Complete Phenanthrene Degradation

Polycyclic aromatic hydrocarbons (PAHs) are highly toxic and persistent organic pollutions that can accumulate in the environment. In this study, an aromatic ring cleavage module, a salicylic acid synthesis module, and a catechol metabolism module were respectively constructed in three Escherichia coli BL21 strains. Subsequently, the engineered strains were cocultured as an artificial consortium for the biodegradation of phenanthrene, a typical PHA. Single factor experiments and response surface methodology were used to identify the optimal degradation conditions, including an inoculation interval of 6 h, inoculation ratio of 1:1:1, and IPTG concentration of 2 mM. Under these conditions, the 7-day degradation ratio of 100 mg/L phenanthrene reached 72.67%. Moreover, the engineered Escherichia coli BL21 strains showed good phenanthrene degradation ability at substrate concentrations 10 mg/L up to 500 mg/L. Enzyme activity assays combined with gas chromatography-mass spectrometry measurements confirmed that the three engineered strains behaved as a synergistic consortium in the phenanthrene degradation process. Based on the analysis of the key metabolites, the engineered bacteria were supplemented at 7-day intervals in batches so that each engineered strain maintained its optimal degradation ability. The 21-day degradation ratio finally reached 90.66%, which was much higher than what was observed with simultaneous inoculation. These findings suggest that the three engineered strains with separate modules constructed in this study offer an attractive solution for removing PAHs from the environment.

Symbiont-Mediated Protection of Acromyrmex Leaf-Cutter Ants from the Entomopathogenic Fungus Metarhizium anisopliae

Many fungus-growing ants engage in a defensive symbiosis with antibiotic-producing ectosymbiotic bacteria in the genus Pseudonocardia, which help protect the ants' fungal mutualist from a specialized mycoparasite, Escovopsis. Here, using germfree ant rearing and experimental pathogen infection treatments, we evaluate if Acromyrmex ants derive higher immunity to the entomopathogenic fungus Metarhizium anisopliae from their Pseudonocardia symbionts. We further examine the ecological dynamics and defensive capacities of Pseudonocardia against M. anisopliae across seven different Acromyrmex species by controlling Pseudonocardia acquisition using ant-nonnative Pseudonocardia switches, in vitro challenges, and in situ mass spectrometry imaging (MSI). We show that Pseudonocardia protects the ants against M. anisopliae across different Acromyrmex species and appears to afford higher protection than metapleural gland (MG) secretions. Although Acromyrmex echinatior ants with nonnative Pseudonocardia symbionts receive protection from M. anisopliae regardless of the strain acquired compared with Pseudonocardia-free conditions, we find significant variation in the degree of protection conferred by different Pseudonocardia strains. Additionally, when ants were reared in Pseudonocardia-free conditions, some species exhibit more susceptibility to M. anisopliae than others, indicating that some ant species depend more on defensive symbionts than others. In vitro challenge experiments indicate that Pseudonocardia reduces Metarhizium conidiospore germination area. Our chemometric analysis using matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) reveals that Pseudonocardia-carrying ants produce more chemical signals than Pseudonocardia-free treatments, indicating that Pseudonocardia produces bioactive metabolites on the Acromyrmex cuticle. Our results indicate that Pseudonocardia can serve as a dual-purpose defensive symbiont, conferring increased immunity for both the obligate fungal mutualist and the ants themselves. IMPORTANCE In some plants and animals, beneficial microbes mediate host immune response against pathogens, including by serving as defensive symbionts that produce antimicrobial compounds. Defensive symbionts are known in several insects, including some leaf-cutter ants where antifungal-producing Actinobacteria help protect the fungal mutualist of the ants from specialized mycoparasites. In many defensive symbioses, the extent and specificity of defensive benefits received by the host are poorly understood. Here, using "aposymbiotic" rearing, symbiont switching experiments, and imaging mass spectrometry, we explore the ecological and chemical dynamics of the model defensive symbiosis between Acromyrmex ants and their defensive symbiotic bacterium Pseudonocardia. We show that the defensive symbiont not only protects the fungal crop of Acromyrmex but also provides protection from fungal pathogens that infect the ant workers themselves. Furthermore, we reveal that the increased immunity to pathogen infection differs among strains of defensive symbionts and that the degree of reliance on a defensive symbiont for protection varies across congeneric ant species. Taken together, our results suggest that Acromyrmex-associated Pseudonocardia have evolved broad antimicrobial defenses that promote strong immunity to diverse fungal pathogens within the ancient fungus-growing ant-microbe symbiosis.

A comparative study at bioprocess and metabolite levels of superhost strain Streptomyces coelicolor M1152 and its derivative M1581 heterologously expressing chloramphenicol biosynthetic gene cluster

Microbial superhost strains should provide an ideal platform for the efficient homologous or heterologous phenotypic expression of biosynthetic gene clusters (BGCs) of new and novel bioactive molecules. Our aim in the current study was to perform a comparative study at the bioprocess and metabolite levels of the previously designed superhost strain Streptomyces coelicolor M1152 and its derivative strain S. coelicolor M1581 heterologously expressing chloramphenicol BGC. Parent strain M1152 was characterized by a higher specific growth rate, specific CO₂ evolution rate, and a higher specific l-glutamate consumption rate as compared with M1581. Intracellular primary central metabolites (nucleoside/sugar phosphates, amino acids, organic acids, and CoAs) were quantified using four targeted LC-MS/MS-based methods. The metabolite pathways in the nonantibiotic producing S. coelicolor host strain were flooded with carbon from both carbon sources, whereas in antibiotic-producing strain, the carbon of l-glutamate seems to be draining out through excreting synthesized antibiotic. The ¹³ C-isotope-labeling experiments revealed the bidirectionality in the glycolytic pathway and reversibility in the non-oxidative part of PPP even with continuous uptake of d-glucose. The change in the primary metabolites due to the insertion of BGC disclosed a clear linkage between the primary and secondary metabolites.

Intracellular Metabolomics Switching Alters Extracellular Acid Production and Insoluble Phosphate Solubilization Behavior in Penicillium oxalicum

This research aims to understand the precise intracellular metabolic processes of how microbes solubilize insoluble phosphorus (Insol-P) to increase bio-available P. Newly isolated Penicillium oxalicum PSF-4 exhibited outstanding tricalcium phosphate (TP) and iron phosphate (IP) solubilization performance—as manifested by microbial growth and the secretion of low-molecular-weight organic acids (LMWOAs). Untargeted metabolomics approach was employed to assess the metabolic alterations of 73 intracellular metabolites induced by TP and IP compared with soluble KH₂PO₄ in P. oxalicum. Based on the changes of intracellular metabolites, it was concluded that (i) the enhanced intracellular glyoxylate and carbohydrate metabolisms increased the extracellular LMWOAs production; (ii) the exposure of Insol-P poses potential effects to P. oxalicum in destructing essential cellular functions, affecting microbial growth, and disrupting amino acid, lipid, and nucleotide metabolisms; and (iii) the intracellular amino acid utilization played a significant role to stimulate microbial growth and the extracellular LMWOAs biosynthesis.

Enzyme-Constrained Models and Omics Analysis of Streptomyces coelicolor Reveal Metabolic Changes that Enhance Heterologous Production

Many biosynthetic gene clusters (BGCs) require heterologous expression to realize their genetic potential, including silent and metagenomic BGCs. Although the engineered Streptomyces coelicolor M1152 is a widely used host for heterologous expression of BGCs, a systemic understanding of how its genetic modifications affect the metabolism is lacking and limiting further development. We performed a comparative analysis of M1152 and its ancestor M145, connecting information from proteomics, transcriptomics, and cultivation data into a comprehensive picture of the metabolic differences between these strains. Instrumental to this comparison was the application of an improved consensus genome-scale metabolic model (GEM) of S. coelicolor. Although many metabolic patterns are retained in M1152, we find that this strain suffers from oxidative stress, possibly caused by increased oxidative metabolism. Furthermore, precursor availability is likely not limiting polyketide production, implying that other strategies could be beneficial for further development of S. coelicolor for heterologous production of novel compounds.

Mining and fine-tuning sugar uptake system for titer improvement of milbemycins in Streptomyces bingchenggensis

Dramatic decrease of sugar uptake is a general phenomenon in Streptomyces at stationary phase, when antibiotics are extensively produced. Milbemycins produced by Streptomyces bingchenggensis are a group of valuable macrolide biopesticides, while the low yield and titer impede their broad applications in agricultural field. Considering that inadequate sugar uptake generally hinders titer improvement of desired products, we mined the underlying sugar uptake systems and fine-tuned their expression in this work. First, we screened the candidates at both genomic and transcriptomic level in S. bingchenggensis. Then, two ATP-binding cassette transporters named TP2 and TP5 were characterized to improve milbemycin titer and yield significantly. Next, the appropriate native temporal promoters were selected and used to tune the expression of TP2 and TP5, resulting in a maximal milbemycin A3/A4 titer increase by 36.9% to 3321 mg/L. Finally, TP2 and TP5 were broadly fine-tuned in another two macrolide biopesticide producers Streptomyces avermitilis and Streptomyces cyaneogriseus, leading to a maximal titer improvement of 34.1% and 52.6% for avermectin B_1a and nemadectin, respectively. This work provides useful transporter tools and corresponding engineering strategy for Streptomyces.

Deciphering the Metabolic Pathway Difference Between Saccharopolyspora pogona and Saccharopolyspora spinosa by Comparative Proteomics and Metabonomics

Butenyl-spinosyn, a secondary metabolite produced by Saccharopolyspora pogona, exhibits strong insecticidal activity than spinosyn. However, the low synthesis capacity and unknown metabolic characteristics of butenyl-spinosyn in wild-type S. pogona limit its broad application and metabolic engineering. Here, we showed that S. pogona exhibited increased glucose consumption ability and growth rate compared with S. spinosa, but the production of butenyl-spinosyn was much lower than that of spinosyn. To further elucidate the metabolic mechanism of these different phenotypes, we performed a comparative proteomic and metabolomic study on S. pogona and S. spinosa to identify the change in the abundance levels of proteins and metabolites. We found that the abundance of most proteins and metabolites associated with glucose transport, fatty acid metabolism, tricarboxylic acid cycle, amino acid metabolism, energy metabolism, purine and pyrimidine metabolism, and target product biosynthesis in S. pogona was higher than that in S. spinosa. However, the overall abundance of proteins involved in butenyl-spinosyn biosynthesis was much lower than that of the high-abundance protein chaperonin GroEL, such as the enzymes related to rhamnose synthesis. We speculated that these protein and metabolite abundance changes may be directly responsible for the above phenotypic changes in S. pogona and S. spinosa, especially affecting butenyl-spinosyn biosynthesis. Further studies revealed that the over-expression of the rhamnose synthetic genes and methionine adenosyltransferase gene could effectively improve the production of butenyl-spinosyn by 2.69- and 3.03-fold, respectively, confirming the reliability of this conjecture. This work presents the first comparative proteomics and metabolomics study of S. pogona and S. spinosa, providing new insights into the novel links of phenotypic change and metabolic difference between two strains. The result will be valuable in designing strategies to promote the biosynthesis of butenyl-spinosyn by metabolic engineering.

Optimized sampling protocol for mass spectrometry-based metabolomics in Streptomyces

In quantitative metabolomics studies, the most crucial step was arresting snapshots of all interesting metabolites. However, the procedure customized for Streptomyces was so rare that most studies consulted the procedure from other bacteria even yeast, leading to inaccurate and unreliable metabolomics analysis. In this study, a base solution (acetone: ethanol = 1:1, mol/mol) was added to a quenching solution to keep the integrity of the cell membrane. Based on the molar transition energy (ET) of the organic solvents, five solutions were used to carry out the quenching procedures. These were acetone, isoamylol, propanol, methanol, and 60% (v/v) methanol. To the best of our knowledge, this is the first report which has utilized a quenching solution with ET values. Three procedures were also adopted for extraction. These were boiling, freezing–thawing, and grinding ethanol. Following the analysis of the mass balance, amino acids, organic acids, phosphate sugars, and sugar alcohols were measured using gas chromatography with an isotope dilution mass spectrometry. It was found that using isoamylol with a base solution (5:1, v/v) as a quenching solution and that freezing–thawing in liquid nitrogen within 50% (v/v) methanol as an extracting procedure were the best pairing for the quantitative metabolomics of Streptomyces ZYJ-6, and resulted in average recoveries of close to 100%. The concentration of intracellular metabolites obtained from this new quenching solution was between two and ten times higher than that from 60% (v/v) methanol, which until now has been the most commonly used solution. Our findings are the first systematic quantitative metabolomics tools for Streptomyces ZYJ-6 and, therefore, will be important references for research in fields such as 13C based metabolic flux analysis, multi-omic research and genome-scale metabolic model establishment, as well as for other Streptomyces.

Combining metabolomics and network analysis to improve tacrolimus production in Streptomyces tsukubaensis using different exogenous feedings

Tacrolimus is widely used as an immunosuppressant in the treatment of various autoimmune diseases. However, the low fermentation yield of tacrolimus has thus far restricted its industrial applications. To solve this problem, the time-series response mechanisms of the intracellular metabolism that were highly correlated with tacrolimus biosynthesis were investigated using different exogenous feeding strategies in S. tsukubaensis. The metabolomic datasets, which contained 93 metabolites, were subjected to weighted correlation network analysis (WGCNA), and eight distinct metabolic modules and seven hub metabolites were identified to be specifically associated with tacrolimus biosynthesis. The analysis of metabolites within each metabolic module suggested that the pentose phosphate pathway (PPP), shikimate and aspartate pathway might be the main limiting factors in the rapid synthesis phase of tacrolimus accumulation. Subsequently, all possible key-limiting steps in the above metabolic pathways were further screened using a genome-scale metabolic network model (GSMM) of S. tsukubaensis. Based on the prediction results, two newly identified targets (aroC and dapA) were overexpressed experimentally, and both of the engineered strains showed higher tacrolimus production. Moreover, the best strain, HT-aroC/dapA, that was engineered to simultaneously enhanced chorismate and lysine biosynthesis was able to produce 128.19 mg/L tacrolimus, 1.64-fold higher than control (78.26 mg/L). These findings represent a valuable addition to our understanding of tacrolimus accumulation in S. tsukubaensis, and pave the way to further production improvements.

The use of stable isotopes in the study of human pathophysiology

The growing prevalence of metabolic diseases including fatty liver disease and Type 2 diabetes has increased the emphasis on understanding metabolism at the mechanistic level and how it is perturbed in disease. Metabolomics is a continually expanding field that seeks to measure metabolites in biological systems during a physiological stimulus or a genetic alteration. Typically, metabolomics studies provide total pool sizes of metabolites rather than dynamic flux measurements. More recently there has been a resurgence in approaches that use stable isotopes (e.g. ²H and ¹³C) for the unambiguous tracking of individual atoms through compartmentalised metabolic networks in humans to determine underlying mechanisms. This is known as metabolic flux analysis and enables the capture of a dynamic picture of the metabolome and its interactions with the genome and proteome. In this review, we describe current approaches using stable isotope labelling in the field of metabolomics and provide examples of studies that led to an improved understanding of glucose, fatty acid and amino acid metabolism in humans, particularly in relation to metabolic disease. Examples include the use of stable isotopes of glucose to study tumour bioenergetics as well as brain metabolism during traumatic brain injury. Lipid tracers have also been used to measure non-esterified fatty acid production whilst amino acid tracers have been used to study the rate of protein digestion on whole body postprandial protein metabolism. In addition, we illustrate the use of stable isotopes for measuring flux in human physiology by providing examples of breath tests to measure insulin resistance and gastric emptying rates.

Soft, chewable gelatin-based pharmaceutical oral formulations: a technical approach

OBJECTIVE

Hard tablets and capsules for oral drug delivery cause problems for people experiencing dysphagia. This work describes the formulation and properties of a gelatin based, self-preserved, and soft chewable tablet as an alternative and novel drug delivery format.

MATERIALS AND METHODS

Gelatin (8.8-10% in 24.7-29% water) constituted the matrix of the soft, semi-solid tablets. Three different pharmaceuticals (Ibuprofen 10%, Acetaminophen 15%, and Meloxicam 1.5%) were tested in this formulation. Microbial stability was controlled by lowering the water activity with a mixture of sorbitol and xylitol (45.6-55%). Rheological properties were tested applying small strain oscillation measurements. Taste masking of ibuprofen soft-chew tablets was achieved by keeping the ibuprofen insoluble at pH 4.5 and keeping the processing temperature below the crystalline-to-amorphous transition temperature.

RESULTS

Soft-chew formulations showed good stability for all three pharmaceuticals (up to 24 months), and the ibuprofen containing formulation exhibited comparable dissolution to a standard oral tablet as well as good microbial stability. The rheological properties of the ibuprofen/gelatin formulation had the fingerprint of a true gelatin gel, albeit higher moduli, and melting temperature.

CONCLUSIONS

The results suggest that easy-to-swallow and well taste-masked soft chewable tablet formulations with extended shelf life are within reach for several active pharmaceutical ingredients (APIs).

Plasma modified PLA electrospun membranes for actinorhodin production intensification in Streptomyces coelicolor immobilized-cell cultivations

Most of industrially relevant bioproducts are produced by submerged cultivations of actinomycetes. The immobilization of these Gram-positive filamentous bacteria on suitable porous supports may prevent mycelial cell-cell aggregation and pellet formation which usually negatively affect actinomycete submerged cultivations, thus, resulting in an improved biosynthetic capability. In this work, electrospun polylactic acid (PLA) membranes, subjected or not to O₂-plasma treatment (PLA-plasma), were used as support for immobilized-cell submerged cultivations of Streptomyces coelicolor M145. This strain produces different bioactive compounds, including the blue-pigmented actinorhodin (ACT) and red-pigmented undecylprodigiosin (RED), and constitutes a model for the study of antibiotic-producing actinomycetes. Wet contact angles and X-ray photoelectron spectroscopy analysis confirmed the increased wettability of PLA-plasma due to the formation of polar functional groups such as carboxyl and hydroxyl moieties. Scanning electron microscope observations, carried out at different incubation times, revealed that S. coelicolor immobilized-cells created a dense "biofilm-like" mycelial network on both kinds of PLA membranes. Cultures of S. coelicolor immobilized-cells on PLA or PLA-plasma membranes produced higher biomass (between 1.5 and 2 fold) as well as higher levels of RED and ACT than planktonic cultures. In particular, cultures of immobilized-cells on PLA and PLA-plasma produced comparable levels of RED that were approximatively 4 and 5 fold higher than those produced by planktonic cultures, respectively. In contrast, levels of ACT produced by immobilized-cell cultures on PLA and PLA-plasma were different, being 5 and 10 fold higher than those of planktonic cultures, respectively. Therefore, this is study demonstrated the positive influence of PLA membrane on growth and secondary metabolite production in S. coelicolor and also revealed that O₂-plasma treated PLA membranes specifically promoted higher ACT production than not treated membranes.

13C-assisted metabolomics analysis reveals the positive correlation between specific erythromycin production rate and intracellular propionyl-CoA pool size in Saccharopolyspora erythraea

Metabolomics analysis is extremely essential to explore the metabolism characteristics of Saccharopolyspora erythraea. The lack of suitable methods for the determination of intracellular metabolites, however, hinders the application of metabolomics analysis for S. erythraea. Acyl-CoAs are important precursors of erythromycin; phosphorylated sugars are intermediate metabolites in EMP pathway or PPP pathway; organic acids are intermediate metabolites in TCA cycle. Reliable determination methods for intracellular acyl-CoAs, phosphorylated sugars, and organic acids of S. erythraea were designed and validated in this study. Using the optimized determination methods, the pool sizes of intracellular metabolites during an erythromycin fermentation process were precisely quantified by isotope dilution mass spectroscopy method. The quantification results showed that the specific erythromycin production rate was positively correlated with the pool sizes of propionyl-CoA as well as many other intracellular metabolites. The experiment under the condition without propanol, which is a precursor of propionyl-CoA and an important substrate in industrial erythromycin production process, also corroborated the correlation between specific erythromycin production rate and intracellular propionyl-CoA pool size. As far as we know, this is the first paper to conduct the metabolomics analysis of S. erythraea, which makes the metabolomics analysis of S. erythraea in the industrial erythromycin production process possible.

NAD(+)-specific glutamate dehydrogenase (EC.1.4.1.2) in Streptomyces coelicolor; in vivo characterization and the implication for nutrient-dependent secondary metabolism

While glutamate and glutamate-rich compounds are widely used for culturing Streptomyces sp., little is known regarding glutamate catabolism at molecular level. Noting the presence of two distinct putative glutamate dehydrogenases (GDH), we constructed knockout mutants of each gene with Streptomyces coelicolor M145 and examined the functionality related to antibiotic production. Out of the two, the sco2999 knockout (ΔgdhB, NAD(+)-specific) showed outstanding effects; it decreased the growth sevenfold but initiated the undecylprodigiosin (RED) production in complex Difco nutrient media which otherwise does not support the production from M145. With glucose supplementation, the growth difference by ΔgdhB disappeared but we could obtain significantly increased actinorhodin (ACT) and RED biosynthesis with the mutant by limiting the glucose content (0.5∼1.0 %, w/v). Complementing the gene to the knockout mutant inhibited the production, confirming its gene specificity. Along with the extended impacts on overall nitrogen metabolism based on the intracellular metabolite analysis and enzyme assays, GdhB and glutamate utilization were shown to interfere with N-acetylglucosamine metabolism and the activity of its associated global transcriptional regulator (DasR). Taken together, GdhB-subjected to the nutritional context-dependent regulation-is proposed as a key member of central nitrogen metabolism to control the secondary metabolism initiation in exploiting the organic nitrogen sources.

Comparative metabolic profiling reveals the key role of amino acids metabolism in the rapamycin overproduction by Streptomyces hygroscopicus

Rapamycin is an important natural macrolide antibiotic with antifungal, immunosuppressive and anticancer activity produced by Streptomyces hygroscopicus. In this study, a mutant strain obtained by ultraviolet mutagenesis displayed higher rapamycin production capacity compared to the wild-type S. hygroscopicus ATCC 29253. To gain insights into the mechanism of rapamycin overproduction, comparative metabolic profiling between the wild-type and mutant strain was performed. A total of 86 metabolites were identified by gas chromatography–mass spectrometry. Pattern recognition methods, including principal component analysis, partial least squares and partial least squares discriminant analysis, were employed to determine the key biomarkers. The results showed that 22 potential biomarkers were closely associated with the increase of rapamycin production and the tremendous metabolic difference was observed between the two strains. Furthermore, metabolic pathway analysis revealed that amino acids metabolism played an important role in the synthesis of rapamycin, especially lysine, valine, tryptophan, isoleucine, glutamate, arginine and ornithine. The inadequate supply of amino acids, or namely “nitrogen starvation” occurred in the mutant strain. Subsequently, the exogenous addition of amino acids into the fermentation medium of the mutant strain confirmed the above conclusion, and rapamycin production of the mutant strain increased to 426.7 mg/L after adding lysine, approximately 5.8-fold of that in the wild-type strain. Finally, the results of real-time PCR and enzyme activity assays demonstrated that dihydrodipicolinate synthase involved with lysine metabolism played vital role in the biosynthesis of rapamycin. These findings will provide a theoretical basis for further improving production of rapamycin.

Tailoring specialized metabolite production in streptomyces

Streptomycetes are prolific producers of a plethora of medically useful metabolites. These compounds are made by complex secondary (specialized) metabolic pathways, which utilize primary metabolic intermediates as building blocks. In this review we discuss the evolution of specialized metabolites and how expansion of gene families in primary metabolism has lead to the evolution of diversity in these specialized metabolic pathways and how developing a better understanding of expanded primary metabolic pathways can help enhance synthetic biology approaches to industrial pathway engineering.

Optimized submerged batch fermentation strategy for systems scale studies of metabolic switching in Streptomyces coelicolor A3(2)

BACKGROUND

Systems biology approaches to study metabolic switching in Streptomyces coelicolor A3(2) depend on cultivation conditions ensuring high reproducibility and distinct phases of culture growth and secondary metabolite production. In addition, biomass concentrations must be sufficiently high to allow for extensive time-series sampling before occurrence of a given nutrient depletion for transition triggering. The present study describes for the first time the development of a dedicated optimized submerged batch fermentation strategy as the basis for highly time-resolved systems biology studies of metabolic switching in S. coelicolor A3(2).

RESULTS

By a step-wise approach, cultivation conditions and two fully defined cultivation media were developed and evaluated using strain M145 of S. coelicolor A3(2), providing a high degree of cultivation reproducibility and enabling reliable studies of the effect of phosphate depletion and L-glutamate depletion on the metabolic transition to antibiotic production phase. Interestingly, both of the two carbon sources provided, D-glucose and L-glutamate, were found to be necessary in order to maintain high growth rates and prevent secondary metabolite production before nutrient depletion. Comparative analysis of batch cultivations with (i) both L-glutamate and D-glucose in excess, (ii) L-glutamate depletion and D-glucose in excess, (iii) L-glutamate as the sole source of carbon and (iv) D-glucose as the sole source of carbon, reveal a complex interplay of the two carbon sources in the bacterium's central carbon metabolism.

CONCLUSIONS

The present study presents for the first time a dedicated cultivation strategy fulfilling the requirements for systems biology studies of metabolic switching in S. coelicolor A3(2). Key results from labelling and cultivation experiments on either or both of the two carbon sources provided indicate that in the presence of D-glucose, L-glutamate was the preferred carbon source, while D-glucose alone appeared incapable of maintaining culture growth, likely due to a metabolic bottleneck at the oxidation of pyruvate to acetyl-CoA.