Enhanced FK506 production inStreptomyces tsukubaensisby rational feeding strategies based on comparative metabolic profiling analysis

Unraveling the role of intra-cellular metabolites in the lactic acid production by novel Bacillus amyloliquefaciens using sugarcane molasses as a substratum

Lactic acid is a versatile, multi-functional organic monomer in various industries, creating worldwide demand. High titer lactic acid production was achieved by novel Bacillus amyloliquefaciens J2V2AA through sugarcane molasses fermentation up to 178 mg mL-1. A metabolomics approach such as combined GC-MS and LC-MS was applied to elucidate the involvement of key metabolites in lactic acid production. The results revealed the participation of 58 known intra-cellular metabolites at various pathways in lactic acid production. Twenty-eight highly up-regulated and down-regulated metabolites were analyzed, and a schematic diagram of a possible lactic acid production pathway was proposed. The produced lactic acid was analyzed through FTIR, UV-Spectrum, and HPLC analysis.

Streamlined identification of strain engineering targets for bioprocess improvement using metabolic pathway enrichment analysis

Metabolomics is a powerful tool for the identification of genetic targets for bioprocess optimisation. However, in most cases, only the biosynthetic pathway directed to product formation is analysed, limiting the identification of these targets. Some studies have used untargeted metabolomics, allowing a more unbiased approach, but data interpretation using multivariate analysis is usually not straightforward and requires time and effort. Here we show, for the first time, the application of metabolic pathway enrichment analysis using untargeted and targeted metabolomics data to identify genetic targets for bioprocess improvement in a more streamlined way. The analysis of an Escherichia coli succinate production bioprocess with this methodology revealed three significantly modulated pathways during the product formation phase: the pentose phosphate pathway, pantothenate and CoA biosynthesis and ascorbate and aldarate metabolism. From these, the two former pathways are consistent with previous efforts to improve succinate production in Escherichia coli. Furthermore, to the best of our knowledge, ascorbate and aldarate metabolism is a newly identified target that has so far never been explored for improving succinate production in this microorganism. This methodology therefore represents a powerful tool for the streamlined identification of strain engineering targets that can accelerate bioprocess optimisation.

Production improvement of FK506 in Streptomyces tsukubaensis by metabolic engineering strategy

AIMS

Study of the effect of isoleucine on the biosynthesis of FK506 and modification of its producing strain to improve the production of FK506.

METHODS AND RESULTS

Metabolomics analysis was conducted to explore key changes in the metabolic processes of Streptomyces tsukubaensis Δ68 in medium with and without isoleucine. In-depth analysis revealed that the shikimate pathway, methylmalonyl-CoA, and pyruvate might be the rate-limiting factors in FK506 biosynthesis. Overexpression of involved gene PCCB1 in S. tsukubaensis Δ68, a high-yielding strain Δ68-PCCB1 was generated. Additionally, the amino acids supplement was further optimized to improve FK506 biosynthesis. Finally, FK506 production was increased to 929.6 mg L-1, which was 56.6% higher than that in the starter strain, when supplemented isoleucine and valine at 9 and 4 g L-1, respectively.

CONCLUSIONS

Methylmalonyl-CoA might be the key rate-limiting factors in FK506 biosynthesis and overexpression of the gene PCCB1 and further addition of isoleucine and valine could increase the yield of FK506 by 56.6%.

Ammonium sulfate supplementation enhances erythromycin biosynthesis by augmenting intracellular metabolism and precursor supply in Saccharopolyspora erythraea

In this study, the cellular metabolic mechanisms regarding ammonium sulfate supplementation on erythromycin production were investigated by employing targeted metabolomics and metabolic flux analysis. The results suggested that the addition of ammonium sulfate stimulates erythromycin biosynthesis. Targeted metabolomics analysis uncovered that the addition of ammonium sulfate during the late stage of fermentation resulted in an augmented intracellular amino acid metabolism pool, guaranteeing an ample supply of precursors for organic acids and coenzyme A-related compounds. Therefore, adequate precursors facilitated cellular maintenance and erythromycin biosynthesis. Subsequently, an optimal supplementation rate of 0.02 g/L/h was determined. The results exhibited that erythromycin titer (1311.1 μg/mL) and specific production rate (0.008 mmol/gDCW/h) were 101.3% and 41.0% higher than those of the process without ammonium sulfate supplementation, respectively. Moreover, the erythromycin A component proportion increased from 83.2% to 99.5%. Metabolic flux analysis revealed increased metabolic fluxes with the supplementation of three ammonium sulfate rates.

Optimization of the precursor supply for an enhanced FK506 production in Streptomyces tsukubaensis

Tacrolimus (FK506) is a macrolide widely used as immunosuppressant to prevent transplant rejection. Synthetic production of FK506 is not efficient and costly, whereas the biosynthesis of FK506 is complex and the level produced by the wild type strain, Streptomyces tsukubaensis, is very low. We therefore engineered FK506 biosynthesis and the supply of the precursor L-lysine to generate strains with improved FK506 yield. To increase FK506 production, first the intracellular supply of the essential precursor lysine was improved in the native host S. tsukubaensis NRRL 18488 by engineering the lysine biosynthetic pathway. Therefore, a feedback deregulated aspartate kinase AskSt* of S. tsukubaensis was generated by site directed mutagenesis. Whereas overexpression of AskSt* resulted only in a 17% increase in FK506 yield, heterologous overexpression of a feedback deregulated AskCg* from Corynebacterium glutamicum was proven to be more efficient. Combined overexpression of AskCg* and DapASt, showed a strong enhancement of the intracellular lysine pool following increase in the yield by approximately 73% compared to the wild type. Lysine is coverted into the FK506 building block pipecolate by the lysine cyclodeaminase FkbL. Construction of a ∆fkbL mutant led to a complete abolishment of the FK506 production, confirming the indispensability of this enzyme for FK506 production. Chemical complementation of the ∆fkbL mutant by feeding pipecolic acid and genetic complementation with fkbL as well as with other lysine cyclodeaminase genes (pipAf, pipASt, originating from Actinoplanes friuliensis and Streptomyces pristinaespiralis, respectively) completely restored FK506 production. Subsequently, FK506 production was enchanced by heterologous overexpression of PipAf and PipASp in S. tsukubaensis. This resulted in a yield increase by 65% compared to the WT in the presence of PipAf from A. friuliensis. For further rational yield improvement, the crystal structure of PipAf from A. friuliensis was determined at 1.3 Å resolution with the cofactor NADH bound and at 1.4 Å with its substrate lysine. Based on the structure the Ile91 residue was replaced by Val91 in PipAf, which resulted in an overall increase of FK506 production by approx. 100% compared to the WT.

Precursor Quantitation Methods for Next Generation Food Production

Food is essential for human survival. Nowadays, traditional agriculture faces challenges in balancing the need of sustainable environmental development and the rising food demand caused by an increasing population. In addition, in the emerging of consumers' awareness of health related issues bring a growing trend towards novel nature-based food additives. Synthetic biology, using engineered microbial cell factories for production of various molecules, shows great advantages for generating food alternatives and additives, which not only relieve the pressure laid on tradition agriculture, but also create a new stage in healthy and sustainable food supplement. The biosynthesis of food components (protein, fats, carbohydrates or vitamins) in engineered microbial cells often involves cellular central metabolic pathways, where common precursors are processed into different proteins and products. Quantitation of the precursors provides information of the metabolic flux and intracellular metabolic state, giving guidance for precise pathway engineering. In this review, we summarized the quantitation methods for most cellular biosynthetic precursors, including energy molecules and co-factors involved in redox-reactions. It will also be useful for studies worked on pathway engineering of other microbial-derived metabolites. Finally, advantages and limitations of each method are discussed.

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.

Improvement of FK506 production via metabolic engineering-guided combinational strategies in Streptomyces tsukubaensis

Background

FK506, a macrolide mainly with immunosuppressive activity, can be produced by various Streptomyces strains. However, one of the major challenges in the fermentation of FK506 is its insufficient production, resulting in high fermentation costs and environmental burdens. Herein, we tried to improve its production via metabolic engineering-guided combinational strategies in Streptomyces tsukubaensis.

Results

First, basing on the genome sequencing and analysis, putative competitive pathways were deleted. A better parental strain L19-2 with increased FK506 production from 140.3 to 170.3 mg/L and a cleaner metabolic background was constructed. Subsequently, the FK506 biosynthetic gene cluster was refactored by in-situ promoter-substitution strategy basing on the regulatory circuits. This strategy enhanced transcription levels of the entire FK506 biosynthetic gene cluster in a fine-tuning manner and dramatically increased the FK506 production to 410.3 mg/mL, 1.41-fold higher than the parental strain L19-2 (170.3 mg/L). Finally, the FK506 production was further increased from 410.3 to 603 mg/L in shake-flask culture by adding L-isoleucine at a final concentration of 6 g/L. Moreover, the potential of FK506 production capacity was also evaluated in a 15-L fermenter, resulting in the FK506 production of 830.3 mg/L.

Conclusion

From the aspects of competitive pathways, refactoring of the FK506 biosynthetic gene cluster and nutrients-addition, a strategy for hyper-production and potentially industrial application of FK506 was developed and a hyper-production strain L19-9 was constructed. The strategy presented here can be generally applicable to other Streptomyces for improvement of FK506 production and streamline hyper-production of other valuable secondary metabolites.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12934-021-01660-w.

Improvement of tacrolimus production in Streptomyces tsukubaensis by mutagenesis and optimization of fermentation medium using Plackett-Burman design combined with response surface methodology

OBJECTIVE

This study was conducted to enhance the production of tacrolimus in Streptomyces tsukubaensis by strain mutagenesis and optimization of the fermentation medium.

RESULTS

A high tacrolimus producing strain S. tsukubaensis FIM-16-06 was obtained by ultraviolet mutagenesis coupled with atmospheric and room temperature plasma mutagenesis.Then, nine variables were screened using Plackett-Burman experimental design, in which soluble starch, peptone and Tween 80 showed significantly affected tacrolimus production. Further studies were carried out employing central composite design to elucidate the mutual interaction between the variables and to work out optimal fermentation medium composition for tacrolimus production. The optimum fermentation medium was found to contain 61.61 g/L of soluble starch, 20.61 g/L of peptone and 30.79 g/L of Tween 80. In the optimized medium, the production of tacrolimus reached 1293 mg/L in shake-flask culture, and reached 1522 mg/L while the scaled-up fermentation was conducted in a 1000 L fermenter, which was about 3.7 times higher than that in the original medium.

CONCLUSIONS

Combining compound mutation with rational medium optimization is an effective approach for improving tacrolimus production, and the optimized fermentation medium could be efficiently used for industrial production.

The Onset of Tacrolimus Biosynthesis in Streptomyces tsukubaensis Is Dependent on the Intracellular Redox Status

The oxidative stress response is a key mechanism that microorganisms have to adapt to changeling environmental conditions. Adaptation is achieved by a fine-tuned molecular response that extends its influence to primary and secondary metabolism. In the past, the role of the intracellular redox status in the biosynthesis of tacrolimus in Streptomyces tsukubaensis has been briefly acknowledged. Here, we investigate the impact of the oxidative stress response on tacrolimus biosynthesis in S. tsukubaensis. Physiological characterization of S. tsukubaensis showed that the onset of tacrolimus biosynthesis coincided with the induction of catalase activity. In addition, tacrolimus displays antioxidant properties and thus a controlled redox environment would be beneficial for its biosynthesis. In addition, S. tsukubaensis ∆ahpC strain, a strain defective in the H₂O₂-scavenging enzyme AhpC, showed increased production of tacrolimus. Proteomic and transcriptomic studies revealed that the tacrolimus over-production phenotype was correlated with a metabolic rewiring leading to increased availability of tacrolimus biosynthetic precursors. Altogether, our results suggest that the carbon source, mainly used for cell growth, can trigger the production of tacrolimus by modulating the oxidative metabolism to favour a low oxidizing intracellular environment and redirecting the metabolic flux towards the increase availability of biosynthetic precursors.

Improvement and Metabolomics-Based Analysis of d-Lactic Acid Production from Agro-Industrial Wastes by Lactobacillus delbrueckii Submitted to Adaptive Laboratory Evolution

To decrease d-lactic acid production cost, sugarcane molasses and soybean meal, low-cost agro-industrial wastes, were selected as feedstock. First, sugarcane molasses was used directly by Lactobacillus delbrueckii S-NL31, and the nutrients were released from soybean meal by protease hydrolysis. Subsequently, to ensure intensive substrate utilization and enhanced d-lactic acid production from sugarcane molasses and soybean meal, adaptation of L. delbrueckii S-NL31 to substrates was performed through adaptive laboratory evolution. After two-phase adaptive laboratory evolution, the evolved strain L. delbrueckii S-NL31-CM3-SBM with improved cell growth and d-lactic acid production on sugarcane molasses and soybean meal was obtained. To decipher the potential reasons for improved fermentation performance, a metabolomics-based approach was developed to profile the differences of intracellular metabolism between initial and evolved strain. The in-depth analysis elucidated how the key factors exerted influence on d-lactic acid biosynthesis. The results revealed that the enhancement of glycolysis pathway and cofactor supply was directly associated with increased lactic acid production, and the reinforcement of pentose phosphate pathway, amino acid metabolism, and oleic acid uptake improved cell survival and growth. These might be the main reasons for significantly improved d-lactic acid production by adaptive laboratory evolution. Finally, fed-batch simultaneous enzymatic hydrolysis of soybean meal and fermentation process by evolved strain resulted in d-lactic acid levels of 112.3 g/L, with an average production efficiency of 2.4 g/(L × h), a yield of 0.98 g/g sugar, and optical purity of 99.6%. The results show the applicability of d-lactic acid production in L. delbrueckii fed on agro-industrial wastes through adaptive laboratory evolution.

Enhanced AmB Production in Streptomyces nodosus by Fermentation Regulation and Rational Combined Feeding Strategy

Amphotericin B is a clinically important polyene macrolide antibiotic with a broad-spectrum antifungal activity. In this work, the addition of key precursors and differential metabolites, combined with staged fermentation process control strategies, was carried out to improve AmB production. Rationally designed addition strategies were proposed as follows: 4 mg/L isopropanol, 1 mM alanine, 1 g/L pyruvate, and 0.025 g/L nicotinamide were supplemented at 24 h. The AmB titer was ultimately enhanced to 6.63 g/L, with 28.5% increase in shake flasks fermentation. To further promote the biosynthesis of AmB, different glucose feeding strategies were investigated and the highest AmB titer (15.78 g/L) was obtained by constant speed fed-batch fermentation in a 5-L fermentor. Subsequently, compared with the batch fermentation (9.89 g/L), a novel combined feeding strategy was ultimately developed to improve the production of AmB by 85.9%, reaching 18.39 g/L that is the highest titer of AmB ever reported so far, in which the optimized components were fed at 24 h and the staged fermentation regulation strategies were used simultaneously. Moreover, the ratio of co-metabolite AmA decreased by 32.3%, from 3.1 to 2.1%. Through the detection of extracellular organic acids, the changes in α-ketoglutaric acid, pyruvate, and citric acid concentrations were identified as the most flexible metabolite nodes to further clarify the potential mechanism under different fermentation regulation strategies. These results demonstrated that the strategies above may provide new guidance for the industrial-scale production of AmB.

Toward fine-tuned metabolic networks in industrial microorganisms

There are numerous microorganisms in nature capable of synthesizing diverse useful compounds; however, these natural microorganisms are generally inefficient in the production of target products on an industrial scale, relative to either chemical synthesis or extraction methods. To achieve industrial production of useful compounds, these natural microorganisms must undergo a certain degree of mutation or effective fine-tuning strategies. This review describes how to achieve an ideal metabolic fine-tuned process, including static control strategies and dynamic control strategies. The static control strategies mainly focus on various matabolic engineering strategies, including protein engineering, upregulation/downregulation, and combinatrorial control of these metabolic engineering strategies, to enhance the flexibility of their application in fine-tuned metabolic metworks. Then, we focus on the dynamic control strategies for fine-tuned metabolic metworks. The design principles derived would guide us to construct microbial cell factories for various useful compounds.

Metabolomics analysis of Actinosynnema pretiosum with improved AP-3 production by enhancing UDP-glucose biosynthesis

Ansamitocin P-3 (AP-3) shows strong anticancer effects and has used as a payload for antibody-drug conjugates. Our previous study have shown that although genetically engineered Actinosynnema pretiosum strains with enhanced UDP-glucose (UDPG) biosynthesis displayed improved AP-3 production compared to the wild-type strain, the increase in yield was far from meeting the industrial demand. In this study, comparative metabolomics analysis complemented with quantitative real-time PCR analysis was performed for the wild-type strain and two mutants (OpgmOugp, ΔzwfΔgnd) to identify possible metabolic bottlenecks and non-intuitive targets for further enhancement of AP-3 production. We observed that enhancing intracellular UDPG availability facilitated the accumulation of intracellular N-demethyl-AP-3 and AP-3, where the transporting of them outside the cell still needs to be developed. We also found that the UDPG biosynthesis was closely associated with the availability of fructose in the medium and a suitable fructose feeding strategy could promote the further improvement of AP-3 titer. In addition, pathway abundance analysis revealed that undesired fatty acid accumulation and down-regulation of amino acid metabolism may be unfavorable for ansamitocin biosynthesis in later stage of production. These results indicate that genetic modification of the UDPG biosynthetic pathways may have pleiotropic effects on AP-3 production. Efforts must be made to eliminate these newly identified metabolic bottlenecks to boost AP-3 production in A. pretiosum.

Enhancement of bleomycin production in Streptomyces verticillus through global metabolic regulation of N-acetylglucosamine and assisted metabolic profiling analysis

BACKGROUND

Bleomycin is a broad-spectrum glycopeptide antitumor antibiotic produced by Streptomyces verticillus. Clinically, the mixture of bleomycin A2 and bleomycin B2 is widely used in combination with other drugs for the treatment of various cancers. As a secondary metabolite, the biosynthesis of bleomycin is precisely controlled by the complex extra-/intracellular regulation mechanisms, it is imperative to investigate the global metabolic and regulatory system involved in bleomycin biosynthesis for increasing bleomycin production.

RESULTS

N-acetylglucosamine (GlcNAc), the vital signaling molecule controlling the onset of development and antibiotic synthesis in Streptomyces, was found to increase the yields of bleomycins significantly in chemically defined medium. To mine the gene information relevant to GlcNAc metabolism, the DNA sequences of dasR-dasA-dasBCD-nagB and nagKA in S. verticillus were determined by chromosome walking. From the results of Real time fluorescence quantitative PCR (RT-qPCR) and electrophoretic mobility shift assays (EMSAs), the repression of the expression of nagB and nagKA by the global regulator DasR was released under induction with GlcNAc. The relief of blmT expression repression by BlmR was the main reason for increased bleomycin production. DasR, however, could not directly affect the expression of the pathway-specific repressor BlmR in the bleomycins gene cluster. With at the beginning of bleomycin synthesis, the supply of the specific precursor GDP-mannose played the key role in bleomycin production. Genetic engineering of the GDP-mannose synthesis pathway indicated that phosphomannose isomerase (ManA) and phosphomannomutase (ManB) were key enzymes for bleomycins synthesis. Here, the blmT, manA and manB co-expression strain OBlmT/ManAB was constructed. Based on GlcNAc regulation and assisted metabolic profiling analysis, the yields of bleomycin A2 and B2 were ultimately increased to 61.79 and 36.9 mg/L, respectively.

CONCLUSIONS

Under GlcNAc induction, the elevated production of bleomycins was mainly associated with the alleviation of the inhibition of BlmT, so blmT and specific precursor synthesis pathways were genetically engineered for bleomycins production improvement. Combination with subsequent metabolomics analysis not only effectively increased the bleomycin yield, but also extended the utilization of chitin-derived substrates in microbial-based antibiotic production.

Enhancement of FK520 production in Streptomyces hygroscopicus by combining traditional mutagenesis with metabolic engineering

FK520 (ascomycin), a 23-membered macrolide with immunosuppressive activity, is produced by Streptomyces hygroscopicus. The problem of low yield and high impurities (mainly FK523) limits the industrialized production of FK520. In this study, the FK520 yield was significantly improved by strain mutagenesis and genetic engineering. First, a FK520 high-producing strain SFK-6-33 (2432.2 mg/L) was obtained from SFK-36 (1588.4 mg/L) through ultraviolet radiation mutation coupled with streptomycin resistance screening. The endogenous crotonyl-CoA carboxylase/reductase (FkbS) was found to play an important role in FK520 biosynthesis, identified with CRISPR/dCas9 inhibition system. FkbS was overexpressed in SFK-6-33 to obtain the engineered strain SFK-OfkbS, which produced 2817.0 mg/L of FK520 resulting from an increase in intracellular ethylmalonyl-CoA levels. In addition, the FK520 levels could be further increased with supplementation of crotonic acid in SFK-OfkbS. Overexpression of acetyl-CoA carboxylase (ACCase), used for the synthesis of malonyl-CoA, was also investigated in SFK-6-33, which improved the FK520 yield to 3320.1 mg/L but showed no significant inhibition in FK523 production. To further enhance FK520 production, FkbS and ACCase combinatorial overexpression strain SFK-OASN was constructed; the FK520 production increased by 44.4% to 3511.4 mg/L, and the FK523/FK520 ratio was reduced from 9.6 to 5.6% compared with that in SFK-6-33. Finally, a fed-batch culture was carried out in a 5-L fermenter, and the FK520 yield reached 3913.9 mg/L at 168 h by feeding glycerol, representing the highest FK520 yield reported thus far. These results demonstrated that traditional mutagenesis combined with metabolic engineering was an effective strategy to improve FK520 production.

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.

Omics-based analyses revealed metabolic responses of Clostridium acetobutylicum to lignocellulose-derived inhibitors furfural, formic acid and phenol stress for butanol fermentation

BACKGROUND

Clostridium acetobutylicum is a model fermentative anaerobe for consolidated bioprocessing of lignocellulose hydrolysates into acetone-butanol-ethanol (ABE). However, the main inhibitors (acids, furans and phenols) ubiquitous in lignocellulose hydrolysates strictly limit the conversion efficiency. Thus, it is essential to understand the underlying mechanisms of lignocellulose hydrolysate inhibitors to identify key industrial bottlenecks that undermine efficient biofuel production. The recently developed omics strategy for intracellular metabolites and protein quantification now allow for the in-depth mapping of strain metabolism and thereby enable the resolution of the underlying mechanisms.

RESULTS

The toxicity of the main inhibitors in lignocellulose hydrolysates against C. acetobutylicum and ABE production was systematically investigated, and the changes in intracellular metabolism were analyzed by metabolomics and proteomics. The toxicity of the main lignocellulose hydrolysate inhibitors at the same dose was ranked as follows: formic acid > phenol > furfural. Metabolomic analysis based on weighted gene coexpression network analysis (WGCNA) revealed that the three inhibitors triggered the stringent response of C. acetobutylicum. Proteomic analysis based on peptide mass spectrometry (MS) supported the above results and provided more comprehensive conclusions. Under the stress of three inhibitors, the metabolites and key enzymes/proteins involved in glycolysis, reductive tricarboxylic acid (TCA) cycle, acetone-butanol synthesis and redox metabolism were lower than those in the control group. Moreover, proteins involved in gluconeogenesis, the oxidative TCA cycle, thiol peroxidase (TPX) for oxidative stress were significantly upregulated, indicating that inhibitor stress induced the stress response and metabolic regulation. In addition, the three inhibitors also showed stress specificity related to fatty acid synthesis, ATP synthesis, nucleic acid metabolism, nicotinic acid metabolism, cell wall synthesis, spore synthesis and flagellum synthesis and so on.

CONCLUSIONS

Integrated omics platforms provide insight into the cellular responses of C. acetobutylicum to cytotoxic inhibitors released during the deconstruction of lignocellulose. This insight allows us to fully improve the strain to adapt to a challenging culture environment, which will prove critical to the industrial efficacy of C. acetobutylicum.

Enhancing the production of tacrolimus by engineering target genes identified in important primary and secondary metabolic pathways and feeding exogenous precursors

Tacrolimus has been widely used as a powerful novel immunosuppressant. The objective of this study was to improve the production of tacrolimus by engineering the target genes of important primary and secondary metabolic pathways and feeding exogenous precursors. Based on the metabonomics analysis, the shikimic acid pathway is an important primary metabolic pathway for the producing tacrolimus. Combined overexpression of shikimate kinase and dehydroquinic acid synthetase genes led to a 33.1% enhancement of tacrolimus production compared to parent strain. To predict the most efficient targets in secondary metabolic pathways for improving the production of tacrolimus, a genome-scale dynamic metabolic network model was used. A knockout of the D-lactate dehydrogenase gene, combined with the overexpression of tryptophane synthase and aspartate 1-decarboxylase genes, led to a 29.8% enhancement of tacrolimus production compared to the parent strain. Finally, we investigated the impact of the genetic manipulations on transcription levels, cell growth, cell morphology and production of tacrolimus by qRT-PCR and scanning electron microscopy to reveal the relationship between the growth of strains, the effects of engineering and fermentation. As the efficient synthesis of tacrolimus requires a rich supply of external substrates, the efficiency of the metabolic pathways that convert these substances is extremely important. The combined addition of three external substrates such as shikimic acid, alanine and the n-dodecane increased tacrolimus production by 49.5%. The insights obtained in this study will help further elucidate the mechanisms by which the identified target genes promote the activity of important primary and secondary metabolic pathways for tacrolimus biosynthesis and provide a new feeding strategy to improve tacrolimus production.

Insight into the surfactin production of Bacillus velezensis B006 through metabolomics analysis

Bacillus velezensis B006 is a biocontrol agent which functions through effective colonization and surfactin production. To reveal the surfactin-producing mechanism, gas chromatography–mass spectrometry based untargeted metabolomics was performed to compare the metabolite profiles of strain B006 grown in industrial media M3 and M4. Based on the statistical and pathway topology analyses, a total of 31 metabolites with a fold change of less than − 1.0 were screened as the significantly altered metabolites, which distributed in 15 metabolic pathways. Fourteen amino acids involving in the metabolisms of alanine/aspartate/glutamate, glycine/serine/threonine, arginine/proline, glutathione/cysteine/methionine and valine/leucine/isoleucine as well as succinic acid in TCA cycle were identified to be the hub metabolites. Aminoacyl-tRNA biosynthesis, glycerolipid metabolism, and pantothenate/CoA biosynthesis also contributed to surfactin production. To the best of our knowledge, this study is the first to investigate the metabolic pathways of B. velezensis on surfactin production, and will benefit the optimization of commercial fermentation for higher surfactin yield.

Enhancement of Pneumocandin B0 Production in Glarea lozoyensis by Low-Temperature Adaptive Laboratory Evolution

The production of pneumocandin B0 is limited by feedback inhibition. Here, low-temperature adaptive laboratory evolution (ALE) was used to improve the production capacity of Glarea lozoyensis by enhancing its membrane permeability. After 50 cycles of ALE, the pneumocandin B0 production of the endpoint strain (ALE50) reached 2131 g/L, which was 32% higher than the starting strain (ALE0). ALE50 showed a changed fatty acid composition of the cell membrane, which-+h increased its permeability by 14%, which in turn increased the secretion ratio threefold. Furthermore, ALE50 showed increased intracellular proline and acetyl-CoA concentrations, superoxide dismutase (SOD), and catalase (CAT) activity, as well as total antioxidant capacity. The slight biomass decrease in ALE50 was accompanied by decreased isocitrate dehydrogenase (ICDH) and glucose-6-phosphate dehydrogenase (G6PDH) activity. Finally, a putative model of the accumulation and secretion of pneumocandin B0 in ALE50 was established. ALE is a promising method to release intracellular feedback inhibition.

Novel osmotic stress control strategy for improved pneumocandin B0 production in Glarea lozoyensis combined with a mechanistic analysis at the transcriptome level

Pneumocandin B₀, the precursor of the antifungal drug caspofungin, is a secondary metabolite of the fungus Glarea lozoyensis. In this study, we investigated the effects of mannitol as the sole carbon source on pneumocandin B₀ production by G. lozoyensis. The osmotic pressure is more important in enhancing pneumocandin B₀ production than is the substrate concentration. Based on the kinetic analysis, an osmotic stress control fed-batch strategy was developed. This strategy led to a maximum pneumocandin B₀ concentration of 2711 mg/L with a productivity of 9.05 mg/L/h, representing 34.67 and 6.47% improvements, respectively, over the best result achieved by the one-stage fermentation. Furthermore, G. lozoyensis accumulated glutamate and proline as compatible solutes to resist osmotic stress, and these amino acids also provided the precursors for the enhanced pneumocandin B₀ production. Osmotic stress also activated ROS (reactive oxygen species)-dependent signal transduction by upregulating the levels of related genes and increasing intracellular ROS levels by 20%. We also provided a possible mechanism for pneumocandin B₀ accumulation based on signal transduction. These findings will improve our understanding of the regulatory mechanisms of pneumocandin B₀ biosynthesis and may be applied to improve secondary metabolite production.

Metabolomics profiling reveals the mechanism of increased pneumocandin B0 production by comparing mutant and parent strains

Metabolic profiling was used to discover mechanisms of increased pneumocandin B₀ production in a high-yield strain by comparing it with its parent strain. Initially, 79 intracellular metabolites were identified, and the levels of 15 metabolites involved in six pathways were found to be directly correlated with pneumocandin B₀ biosynthesis. Then by combining the analysis of key enzymes, acetyl-CoA and NADPH were identified as the main factors limiting pneumocandin B₀ biosynthesis. Other metabolites, such as pyruvate, α-ketoglutaric acid, lactate, unsaturated fatty acids and previously unreported metabolite γ-aminobutyric acid were shown to play important roles in pneumocandin B₀ biosynthesis and cell growth. Finally, the overall metabolic mechanism hypothesis was formulated and a rational feeding strategy was implemented that increased the pneumocandin B₀ yield from 1821 to 2768 mg/L. These results provide practical and theoretical guidance for strain selection, medium optimization, and genetic engineering for pneumocandin B₀ production.

Analysis and validation of the pho regulon in the tacrolimus-producer strain Streptomyces tsukubaensis: differences with the model organism Streptomyces coelicolor

Inorganic and organic phosphate controls both primary and secondary metabolism in Streptomyces genus. Metabolism regulation by phosphate in Streptomyces species is mediated by the PhoR-PhoP two-component system. Response regulator PhoP binds to conserved sequences of 11 nucleotides called direct repeat units (DRus), whose organization and conservation determine the binding of PhoP to distinct promoters. Streptomyces tsukubaensis is the industrial producer of the clinical immunosuppressant tacrolimus (FK506). A bioinformatic genome analysis detected several genes with conserved PHO boxes involved in phosphate scavenging and transport, nitrogen regulation, and secondary metabolite production. In this article, the PhoP regulation has been confirmed by electrophoretic mobility shift assays (EMSA) of the most relevant members of the traditional pho regulon such as the two-component system PhoR-P or genes involved in high-affinity phosphate transport (pstSCAB) and low-affinity phosphate transport (pit). However, the PhoP control over phosphatase genes in S. tsukubaensis is significantly different from the pattern reported in the model bacteria Streptomyces coelicolor. Thus, neither the alkaline phosphatase PhoA nor PhoD is regulated by PhoP. On the contrary, the binding of PhoP to the promoter of a novel putative phosphatase PhoX was confirmed. A crosstalk of the PhoP and GlnR regulators, which balances phosphate and nitrogen utilization, also occurs in S. tsukubaensis but slightly modified. Finally, PhoP regulates genes, like afsS, that link phosphate control and secondary metabolite production in S. tsukubaensis. In summary, there are notable differences between the regulation of specific genes of the pho regulon in S. tsukubaensis and the model organism S. coelicolor.

Metabolomic and proteomic analysis of D-lactate-producing Lactobacillus delbrueckii under various fermentation conditions

As an important feedstock monomer for the production of biodegradable stereo-complex poly-lactic acid polymer, D-lactate has attracted much attention. To improve D-lactate production by microorganisms such as Lactobacillus delbrueckii, various fermentation conditions were performed, such as the employment of anaerobic fermentation, the utilization of more suitable neutralizing agents, and exploitation of alternative nitrogen sources. The highest D-lactate titer could reach 133 g/L under the optimally combined fermentation condition, increased by 70.5% compared with the control. To decipher the potential mechanisms of D-lactate overproduction, the time-series response of intracellular metabolism to different fermentation conditions was investigated by GC-MS and LC-MS/MS-based metabolomic analysis. Then the metabolomic datasets were subjected to weighted correlation network analysis (WGCNA), and nine distinct metabolic modules and eight hub metabolites were identified to be specifically associated with D-lactate production. Moreover, a quantitative iTRAQ-LC-MS/MS proteomic approach was employed to further analyze the change of intracellular metabolism under the combined fermentation condition, identifying 97 up-regulated and 42 down-regulated proteins compared with the control. The in-depth analysis elucidated how the key factors exerted influence on D-lactate biosynthesis. The results revealed that glycolysis and pentose phosphate pathways, transport of glucose, amino acids and peptides, amino acid metabolism, peptide hydrolysis, synthesis of nucleotides and proteins, and cell division were all strengthened, while ATP consumption for exporting proton, cell damage, metabolic burden caused by stress response, and bypass of pyruvate were decreased under the combined condition. These might be the main reasons for significantly improved D-lactate production. These findings provide the first omics view of cell growth and D-lactate overproduction in L. delbrueckii, which can be a theoretical basis for further improving the production of D-lactate.

Unraveling Nutritional Regulation of Tacrolimus Biosynthesis in Streptomyces tsukubaensis through omic Approaches

Streptomyces tsukubaensis stands out among actinomycetes by its ability to produce the immunosuppressant tacrolimus. Discovered about 30 years ago, this macrolide is widely used as immunosuppressant in current clinics. Other potential applications for the treatment of cancer and as neuroprotective agent have been proposed in the last years. In this review we introduce the discovery of S. tsukubaensis and tacrolimus, its biosynthetic pathway and gene cluster (fkb) regulation. We have focused this work on the omic studies performed in this species in order to understand tacrolimus production. Transcriptomics, proteomics and metabolomics have improved our knowledge about the fkb transcriptional regulation and have given important clues about nutritional regulation of tacrolimus production that can be applied to improve production yields. Finally, we address some points of S. tsukubaensis biology that deserve more attention.

Manipulating the expression of SARP family regulator BulZ and its target gene product to increase tacrolimus production

Tacrolimus (FK506), an effective immunosuppressant, is widely used in the treatment of autoimmune diseases. In this study, we identified that BulZ, a Streptomyces antibiotic regulatory protein (SARP) family regulator, acted as a positive regulator for spore differentiation and tacrolimus production. A knockout of bulZ resulted in a 47.5% decrease of tacrolimus production and a delay of spore differentiation. Using quantitative real-time PCR (qRT-PCR) analysis and electrophoretic mobility shift assays (EMSAs), it was found that BulZ directly activated the transcriptions of bulZ and bulS2, a putative γ-butyrolactone (GBL) synthetase, and bulS2 was shown to play a positive role in tacrolimus biosynthesis. Meanwhile, BulZ was able to indirectly regulate the transcriptions of the cluster-linked activator genes tcs7 and fkbN, as well as the GBL receptor gene bulR1. STSU_RS22595, which encoded a WhiB family transcriptional regulator, was found to be a previously unknown potential target gene of BulZ based on a whole-genome search of the conserved sequence (5'-TSVAVVVNVNBTSRAGNN-3') of the SARP-binding motifs. Although overexpression of STSU_RS22595 did not result in an obvious enhancement of tacrolimus yield, STSU_RS22595 might have important effects on the spore differentiation process. Finally, co-overexpression of bulZ and its target gene bulS2 improved tacrolimus production by 36% compared to the control strain, reaching 324 mg/L. The insights obtained in this study will help further elucidate the regulatory mechanism of tacrolimus biosynthesis and provide new avenues for further improvement of tacrolimus production.

Metabolome- and genome-scale model analyses for engineering of Aureobasidium pullulans to enhance polymalic acid and malic acid production from sugarcane molasses

BACKGROUND

Polymalic acid (PMA) is a water-soluble biopolymer with many attractive properties for food and pharmaceutical applications mainly produced by the yeast-like fungus Aureobasidium pullulans. Acid hydrolysis of PMA, resulting in release of the monomer l-malic acid (MA), which is widely used in the food and chemical industry, is a competitive process for producing bio-based platform chemicals.

RESULTS

In this study, the production of PMA and MA from sucrose and sugarcane molasses by A. pullulans was studied in shake flasks and bioreactors. Comparative metabolome analysis of sucrose- and glucose-based fermentation identified 81 intracellular metabolites and demonstrated that pyruvate from the glycolysis pathway may be a key metabolite affecting PMA synthesis. In silico simulation of a genome-scale metabolic model (iZX637) further verified that pyruvate carboxylase (pyc) via the reductive tricarboxylic acid cycle strengthened carbon flux for PMA synthesis. Therefore, an engineered strain, FJ-PYC, was constructed by overexpressing the pyc gene, which increased the PMA titer by 15.1% compared with that from the wild-type strain in a 5-L stirred-tank fermentor. Sugarcane molasses can be used as an economical substrate without any pretreatment or nutrient supplementation. Using fed-batch fermentation of FJ-PYC, we obtained the highest PMA titers (81.5, 94.2 g/L of MA after hydrolysis) in 140 h with a corresponding MA yield of 0.62 g/g and productivity of 0.67 g/L h.

CONCLUSIONS

We showed that integrated metabolome- and genome-scale model analyses were an effective approach for engineering the metabolic node for PMA synthesis, and also developed an economical and green process for PMA and MA production from renewable biomass feedstocks.

Rational design of a synthetic Entner-Doudoroff pathway for enhancing glucose transformation to isobutanol in Escherichia coli

Isobutanol as a more desirable biofuel has attracted much attention. In our previous work, an isobutanol-producing strain Escherichia coli LA09 had been obtained by rational redox status improvement under guidance of the genome-scale metabolic model. However, the low transformation from sugar to isobutanol is a limiting factor for isobutanol production by E. coli LA09. In this study, the intracellular metabolic profiles of the isobutanol-producing E. coli LA09 with different initial glucose concentrations were investigated and the metabolic reaction of fructose 6-phosphate to 1, 6-diphosphate fructose in glycolytic pathway was identified as the rate-limiting step of glucose transformation. Thus, redesigned carbon catabolism was implemented by altering flux of sugar metabolism. Here, the heterologous Entner-Doudoroff (ED) pathway from Zymomonas mobilis was constructed, and the adaptation of upper and lower parts of ED pathway was further improved with artificial promoters to alleviate the accumulation of toxic intermediate metabolite 2-keto-3-deoxy-6-phospho-gluconate (KDPG). Finally, the best isobutanol-producing E. coli ED02 with higher glucose transformation and isobutanol production was obtained. In the fermentation of strain E. coli ED02 with 45 g/L initial glucose, the isobutanol titer, yield and average producing rate were, respectively, increased by 56.8, 47.4 and 88.1% to 13.67 g/L, 0.50 C-mol/C-mol and 0.456 g/(L × h) in a shorter time of 30 h, compared with that of the starting strain E. coli LA09.

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.

Fluorescence Polarization Assay for Small Molecule Screening of FK506 Biosynthesized in 96-Well Microtiter Plates

The fluorescence polarization (FP) assay has been widely used to study enzyme kinetics, antibody-antigen interactions, and other biological interactions. We propose that the FP assay can be adapted as a high-throughput and potentially widely applicable screen for small molecules. This is useful in metabolic engineering, which is a promising approach to synthesizing compounds of pharmaceutical, agricultural, and industrial importance using bioengineered strains. There, the development of high-yield strains is often a costly and time-consuming process. This problem can be addressed by generating and testing large mutant strain libraries. However, a current key bottleneck is the lack of high-throughput screens to detect the small molecule products. The FP assay is quantitative, sensitive, fast, and cheap. As a proof of principle, we established the FP assay to screen for FK506 (tacrolimus) produced by Streptomyces tsukubaensis, which was cultivated in 96-well plates. An ultraviolet mutagenized library of 160 colonies was screened to identify strains showing higher FK506 productivities. The FP assay has the potential to be generalized to detect a wide range of other small molecules.

Integrating multi-omics analyses of Nonomuraea dietziae to reveal the role of soybean oil in [(4'-OH)MeLeu]4-CsA overproduction

Background

Nonomuraea dietziae is a promising microorganism to mediate the region-specific monooxygenation reaction of cyclosporine A (CsA). The main product [(4′-OH)MeLeu]⁴-CsA possesses high anti-HIV/HCV and hair growth-stimulating activities while avoiding the immunosuppressive effect of CsA. However, the low conversion efficiency restricts the clinical application. In this study, the production of [(4′-OH)MeLeu]⁴-CsA was greatly improved by 55.6% from 182.8 to 284.4 mg/L when supplementing soybean oil into the production medium, which represented the highest production of [(4′-OH)MeLeu]⁴-CsA so far.

Results

To investigate the effect of soybean oil on CsA conversion, some other plant oils (corn oil and peanut oil) and the major hydrolysates of soybean oil were fed into the production medium, respectively. The results demonstrated that the plant oils, rather than the hydrolysates, could significantly improve the [(4′-OH)MeLeu]⁴-CsA production, suggesting that soybean oil might not play its role in the lipid metabolic pathway. To further unveil the mechanism of [(4′-OH)MeLeu]⁴-CsA overproduction under the soybean oil condition, a proteomic analysis based on the two-dimensional gel electrophoresis coupled with MALDI TOF/TOF mass spectrometry was implemented. The results showed that central carbon metabolism, genetic information processing and energy metabolism were significantly up-regulated under the soybean oil condition. Moreover, the gas chromatography-mass spectrometry-based metabolomic analysis indicated that soybean oil had a great effect on amino acid metabolism and tricarboxylic acid cycle. In addition, the transcription levels of cytochrome P450 hydroxylase (CYP) genes for CsA conversion were determined by RT-qPCR and the results showed that most of the CYP genes were up-regulated under the soybean oil condition.

Conclusions

These findings indicate that soybean oil could strengthen the primary metabolism and the CYP system to enhance the mycelium growth and the monooxygenation reaction, respectively, and it will be a guidance for the further metabolic engineering of this strain.

Electronic supplementary material

The online version of this article (doi:10.1186/s12934-017-0739-0) contains supplementary material, which is available to authorized users.

Uncertainty budgeting in fold change determination and implications for non-targeted metabolomics studies in model systems

Uncertainty budgeting provides error intervals for fold change values and complements significance testing in non-targeted metabolomics.

FK506, an Immunosuppressive Drug, Induces Autophagy by Binding to the V-ATPase Catalytic Subunit A in Neuronal Cells

The drug FK506 (tacrolimus, fujimycin) exerts its immunosuppressive effects by regulating the nuclear factor of the activated T-cell (NFAT) family of transcription factors. However, FK506 also exhibits neuroprotective effects, but its direct target proteins that mediate these effects have not been determined. To identify the target proteins responsible for FK506's neuroprotective effects, the drug affinity responsive target stability (DARTS) method was performed using label-free FK506, and LC-MS/MS analysis of the FK506-treated proteome was also performed. Using DARTS and LC-MS/MS analyses in combination with reference studies, V-ATPase catalytic subunit A (ATP6V1A) was identified as a new target protein of FK506. The biological relevance of ATP6V1A in mediating the neuroprotective effects of FK506 was validated by analyzing FK506 activity with respect to autophagy via acridine orange staining and transcription factor EB (TFEB) translocation assay. These analyses demonstrated that the binding of FK506 with ATP6V1A induces autophagy by activating the translocation of TFEB from the cytosol into the nucleus. Because autophagy has been identified as a mechanism for treating neurodegenerative diseases and because we have demonstrated that FK506 induces autophagy, this study demonstrates that FK506 is a possible new therapy for treating neurodegenerative diseases.

FkbN and Tcs7 are pathway-specific regulators of the FK506 biosynthetic gene cluster in Streptomyces tsukubaensis L19

FK506 (tacrolimus), which is produced by many Streptomyces strains, is clinically used as an immunosuppressive agent and for treatment of inflammatory skin diseases. Here, we identified that the FK506 biosynthetic gene cluster in an industrial FK506-producing strain Streptomyces tsukubaensis L19 is organized as eight transcription units. Two pathway-specific regulators, FkbN and Tcs7, involved in FK506 biosynthesis from S. tsukubaensis L19 were characterized in vivo and in vitro. FkbN activates the transcription of six transcription units in FK506 biosynthetic gene cluster, and Tcs7 activates the transcription of fkbN. In addition, the DNA-binding specificity of FkbN was determined. Finally, a high FK506-producing strain was constructed by overexpression of both fkbN and tcs7 in S. tsukubaensis L19, which improved FK506 production by 89 % compared to the parental strain.