Impact of nitrogen concentration on validamycin A production and related gene transcription in fermentation of Streptomyces hygroscopicus 5008

Enhanced docosahexaenoic acid production from cane molasses by engineered and adaptively evolved Schizochytrium sp

Cane molasses (CM) is a sugar-rich agro-industrial byproduct. The purpose of this study is to synthesize docosahexaenoic acid (DHA) in Schizochytrium sp. by using CM. The single factor analysis showed that sucrose utilization was the main factor limiting the utilization of CM. Therefore, the endogenous sucrose hydrolase (SH) was overexpressed in Schizochytrium sp., which enhanced the sucrose utilization rate 2.57-fold compared to the wild type. Furthermore, adaptive laboratory evolution was used to further improve sucrose utilization from CM. Comparative proteomics and RT-qPCR were used out to analyze the metabolic differences of evolved strain grown on CM and glucose, respectively. Finally, a constant flow rate CM feeding strategy was implemented, whereby the DHA titer and lipid yield of the final strain OSH-end reached 25.26 g/L and 0.229 g/g sugar, respectively. This study demonstrated the CM is a cost-effective carbon source for industrial DHA fermentation.

Co-production of polyhydroxybutyrate (PHB) and coenzyme Q10 (CoQ10) via no-sugar fermentation—a case by Methylobacterium sp. XJLW

Purpose

To explore a competitive PHB-producing fermentation process, this study evaluated the potential for Methylobacterium sp. XJLW to produce simultaneously PHB and coenzyme Q10 (CoQ10) using methanol as sole carbon and energy source.

Methods

The metabolic pathways of PHB and CoQ10 biosynthesis in Methylobacterium sp. XJLW were first mined based on the genomic and comparative transcriptomics information. Then, real-time fluorescence quantitative PCR (RT-qPCR) was employed for comparing the expression level of important genes involved in PHB and CoQ10 synthesis pathways’ response to methanol and glucose. Transmission electron microscope (TEM), gas chromatography/mass spectrometry (GC-MS), nuclear magnetic resonance (NMR), Fourier transformation infrared spectrum (FT-IR), and liquid chromatography/mass spectrometry (LC-MS) methods were used to elucidate the yield and structure of PHB and CoQ10, respectively. PHB and CoQ10 productivity of Methylobacterium sp. XJLW were evaluated in Erlenmeyer flask for medium optimization, and in a 5-L bioreactor for methanol fed-batch strategy according to dissolved oxygen (DO) and pH control.

Results

Comparative genomics analysis showed that the PHB and CoQ10 biosynthesis pathways co-exist in Methylobacterium sp. XJLW. Transcriptomics analysis showed that the transcription level of key genes in both pathways responding to methanol was significantly higher than that responding to glucose. Correspondingly, strain Methylobacterium sp. XJLW can produce PHB and CoQ10 simultaneously with higher yield using cheap and abundant methanol than using glucose as sole carbon and energy source. The isolated products showed the structure characteristics same to that of standard PHB and CoQ10. The optimal medium and cultural conditions for PHB and CoQ10 co-production by Methylobacterium sp. XJLW was in M3 medium containing 7.918 g L-1 methanol, 0.5 g L-1 of ammonium sulfate, 0.1% (v/v) of Tween 80, and 1.0 g L-1 of sodium chloride, under 30 °C and pH 7.0. In a 5-L bioreactor coupled with methanol fed-batch process, a maximum DCW value (46.31 g L-1) with the highest yields of PHB and CoQ10, reaching 6.94 g L-1 and 22.28 mg L-1, respectively.

Conclusion

Methylobacterium sp. XJLW is potential for efficiently co-producing PHB and CoQ10 employing methanol as sole carbon and energy source. However, it is still necessary to further optimize fermentation process, and genetically modify strain pathway, for enhanced production of PHB and CoQ10 simultaneously by Methylobacterium sp. XJLW. It also suggests a potential strategy to develop efficiently co-producing other high-value metabolites using methanol-based bioprocess.

Understanding high ε-poly-l-lysine production by Streptomyces albulus using pH shock strategy in the level of transcriptomics

ε-Poly-l-lysine (ε-PL) is a natural food preservative, which exhibits antimicrobial activity against a wide spectra of microorganisms. The production of ε-PL was significantly enhanced by pH shock in our previous study, but the underlying mechanism is poorly understood. According to transcriptional and physiological analyses in this study, the mprA/B and pepD signal transduction system was first proved to be presented and activated in Streptomyces albulus M-Z18 by pH shock, which positively regulated the transcription of ε-PL synthetase (Pls) gene and enhanced the Pls activity during fermentation. Furthermore, pH shock changed the ratio of unsaturation to saturation fatty acid in the membrane through up-regulating the transcription of fatty acid desaturase genes (SAZ_RS14940, SAZ_RS14945). In addition, pH shock also enhanced the transcription of cytochrome c oxidase (SAZ_RS15070, SAZ_RS15075), ferredoxin reductase (SAZ_RS34975) and iron sulfur protein (SAZ_RS31410) genes, and finally resulted in the improvement of cell respiratory activity. As a result, pH shock was considered to influence a wide range of proteins including regulators, fatty acid desaturase, respiratory chain component, and ATP-binding cassette transporter during fermentation. These combined influences might contribute to enhanced ε-PL productivity with pH shock.

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.

Development of a strategy for the production of docosahexaenoic acid by Schizochytrium sp. from cane molasses and algae-residue

The aim of this work was to reduce the algae-residue emission and make use of cane molasses as fermentation materials for docosahexaenoic acid (DHA) fermentaion by Schizochytrium sp., which further could cut the cost of DHA production. Algae-residue and cane molasses were respectively used as nitrogen and carbon sources to replace yeast extract and glucose. A significant DHA yield of 18.58 g/L was obtained using algae-residue, while cane molasses could not be used well as sole carbon source due to the presence of undesirable substance. A two-stage culture strategy with glucose followed by pretreated cane molasses as carbon source was developed, resulting in a final DHA yield of 15.22 g/L. This study therefore offers an economical and green strategy for DHA production by Schizochytrium sp.

Biosynthesis and Metabolic Engineering of Pseudo-oligosaccharides

Pseudo-oligosaccharides are microbial-derived secondary metabolites whose chemical structures contain pseudosugars (glycomimetics). Due to their high resemblance to the molecules of life (carbohydrates), most pseudo-oligosaccharides show significant biological activities. Some of them have been used as drugs to treat human and plant diseases. Because of their significant economic value, efforts have been put into understanding their biosynthesis, optimizing their fermentation conditions, and engineering their metabolic pathways to obtain better production yields. A number of unusual enzymes participating in diverse biosynthetic pathways to pseudo-oligosaccharides have been reported. Various methods and conditions to improve the production yields of the target compounds and eliminate byproducts have also been developed. This review article describes recent studies on the biosynthesis, fermentation optimization, and metabolic engineering of high-value pseudo-oligosaccharides.

Alkaline pH shock enhanced production of validamycin A in fermentation of Streptomyces hygroscopicus

Validamycin A (Val-A) is produced by Streptomyces as a secondary metabolite with wide agricultural applications of controlling rice sheath blight, false smut and damping-off diseases. The effect of alkaline pH shock on enhancing Val-A production and its mechanism were investigated. A higher yield of Val-A was achieved by NaOH shock once or several times together with faster protein synthesis and sugar consumption and alkaline pH shock can increase Val-A production by 27.43%. Transcription of genes related to amino acid metabolism, carbon metabolism and electron respiratory chain was significantly up-regulated, accompanied by the substantial increase of respiratory activity and glutamate concentration. Val-A production was promoted by a series of complex mechanisms and made a response to pH stress signal, which led to the enhancement of glutamate metabolism and respiration activity. The obtained information will facilitate future studies for antibiotic yield improvement and the deep revealment of molecular mechanism.

Impact of pH regulation on multicopper oxidase production and swarming motility in the bacterium Proteus hauseri ZMd44

Proteus hauseri ZMd44, a biodecolorizing bacterium, has been known to produce electricity and multicopper oxidase (Mco-laccase) under copper induction. However, optimization and regulation of production have not been explored. This study is the first attempt to evaluate several parameters on biomass and Mco-laccase production of P. hauseri ZMd44. Through orthogonal experiments with Taguchi's L9, it was found that P. hauseri ZMd44 was sensitive to pH value. The cells grew relatively quickly at pH 7, thus the biomass and Mco-laccase production reached 1.66 g/L and 1043.6 U/L, respectively. Higher pH values also influenced the swarming motility, which is an important characteristic of P. hauseri ZMd44 that affects urinary tract infection. The swarming circle and the diameter of the swarm, represented by the motility velocity, were found to be more controlled after 24 h of growth at pH 6. The swarming ability of P. hauseri was completely inhibited by the addition of 3 mM copper or zinc ions. Therefore, the Mco-laccase and swarming motility could be controlled by regulating pH and ion content.

Significance of oxygen carriers and role of liquid paraffin in improving validamycin A production

Validamycin A (Val-A) synthesized by Streptomyces hygroscopicus 5008 is widely used as a high-efficient antibiotic to protect plants from sheath blight disease. A novel fermentation strategy was introduced to stimulate Val-A production by adding oxygen carriers. About 58 % increase in Val-A production was achieved using liquid paraffin. Further, biomass, carbon source, metabolic genes, and metabolic enzymes were studied. It was also found that the supplementation of liquid paraffin increased the medium dissolved oxygen and intracellular oxidative stress level. The expression of the global regulators afsR and soxR sensitive to ROS, ugp catalyzing synthesis of Val-A precursor, and Val-A structural genes was enhanced. The change of the activities of glucose-6-phosphate dehydrogenase and glyceraldehyde 3-phosphate dehydrogenase was observed, which reflected the redirection of carbon metabolic flux. Based on these results, liquid paraffin addition as an oxygen carrier could be a useful technique in industrial production of Val-A and our study revealed a redox-based secondary metabolic regulation in S. hygroscopicus 5008, which provided a new insight into the regulation of the biosynthesis of secondary metabolites.

Novel spectrophotometric approach for determination of validamycin A in fermentation of Streptomyces hygroscopicus

Validamycin A (Val-A), produced by Streptomyces hygroscopicus 5008 in industrial fermentation, is one of the most widely used anti-fungal agro-antibiotics in Asia and high performance liquid chromatography (HPLC) assay is usually used to determine the production of Val-A. A new approach to determine Val-A by spectrophotometer is developed. During the fermentation of S. hygroscopicus 5008, a pigment secretion was found along with the Val-A biosynthesis. There was a stable relationship between the concentration of Val-A and spectral absorption (SA) value of this pigment at 450 nm, even in different fermentation cultures or conditions. Using SA value as interior label, a rapid spectrophotometric method for determining Val-A production was established. In comparing Val-A productivity by HPLC method with that by SA method, the relative standard deviation (R.S.D.) was 0.007 (less than 0.05, no variation) and the conditional probability [Pr(T < t)] was 0.3491 (greater than 0.05, no difference) at the optimal time point of Val-A fermentation, which demonstrated SA method was as stable and accurate as standard HPLC method. It was applied successfully to finding positive strains with high Val-A productivity and short fermentation time. SA assay is an accurate and cost-effective method for measuring Val-A and screening high-producing strains, and this work provides a new insight for rapid quantitative analysis of antibiotics in fermentation of pigment-producing strains.

Production of validamycin A from hemicellulose hydrolysate by Streptomyces hygroscopicus 5008

Validamycin A (VAL-A) is an important agricultural antibiotic produced by Streptomyces hygroscopicus 5008, which uses starch as carbon source occupying about 20% of total production cost. To reduce the medium cost, corncob hydrolysate - a hemicellulose hydrolysate was applied as a low-cost substrate to VAL-A fermentation. It was found that three major sugars in corncob hydrolysate including d-glucose, d-xylose and l-arabinose could all be utilized by S. hygroscopicus 5008 to produce VAL-A while d-xylose was the main contributor. A higher VAL-A production titer from d-xylose was achieved by using a genetically engineered strain TC03 derived from S. hygroscopicus 5008, which resulted in 1.27-fold improvement of VAL-A production from the medium containing 13% (v/v) corncob hydrolysate compared to that by its original strain. A medium cost analysis was done and compared with previous reports. This work indicates a great potential of the hemicellulose hydrolysate as substrate for antibiotic fermentation.

Economical production of poly(ε-l-lysine) and poly(l-diaminopropionic acid) using cane molasses and hydrolysate of streptomyces cells by Streptomyces albulus PD-1

Poly(ε-L-lysine) (ε-PL) and poly(L-diaminopropionic acid) (PDAP) co-production by Streptomyces albulus PD-1 from cane molasses and hydrolysate of strepyomyces cells (HSC) was investigated for the first time in this study. The optimal initial total sugar concentration of the cane molasses pretreated with sulfuric acid was determined to be 20 g L(-1), and HSC could substitute for yeast extract for ε-PL and PDAP co-production. When fed-batch fermentation was performed in 1t fermentor with pretreated cane molasses and HSC, 20.6 ± 0.5 g L(-1) of ε-PL and 5.2 ± 0.6 g L(-1) of PDAP were obtained. The amount of strepyomyces cells obtained in one fed-batch fermentation is sufficient to prepare the HSC to satisfy the demand of subsequent fermentations, thus the self-cycling of organic nitrogen source becomes available. These results suggest that the low-cost cane molasses and HSC can be used for the economical production of ε-PL and PDAP by S. albulus PD-1.

Daptomycin antibiotic production processes in fed-batch fermentation by Streptomyces roseosporus NRRL11379 with precursor effect and medium optimization

Sodium decanoate was first found to be an effective precursor for synthesis of daptomycin from Streptomyces roseosporus NRRL11379 which was increased to 71.55-fold, compared with decanoic acid. The optimal flow rate of precursor was at 600 mg/(L day) after 48 h fermentation. From protein analysis via SDS-PAGE and identification of Tandem MS/MS afterwards, it deciphered that guanosine pentaphosphate synthetase, PNPase, tripeptidylamino peptidase primarily dealing with daptomycin synthesis. By applying Taguchi's L16 in culture optimization, the best yield was obtained from the medium with 60 g/L dextrin, 10 g/L dextrose, 1.0 g/L molasses, and 8 g/L yeast extract, respectively. The fed-batch fermentation, applied with feedback control of dextrin, stimulated the production up to 812 mg/L at 288 h. To our best knowledge, the daptomycin production in this study is significantly higher than that in previous studies and can make it more widely used in pharmaceutical industry.