The glucose RQ-feedback control leading to improved erythromycin production by a recombinant strain Saccharopolyspora erythraea ZL1004 and its scale-up to 372-m3 fermenter

Coupled strategy based on regulator manipulation and medium optimization empowers the biosynthetic overproduction of lincomycin

The biosynthesis of bioactive secondary metabolites, specifically antibiotics, is of great scientific and economic importance. The control of antibiotic production typically involves different processes and molecular mechanism. Despite numerous efforts to improve antibiotic yields, joint engineering strategies for combining genetic manipulation with fermentation optimization remain finite. Lincomycin A (Lin-A), a lincosamide antibiotic, is industrially fermented by Streptomyces lincolnensis. Herein, the leucine-responsive regulatory protein (Lrp)-type regulator SLCG_4846 was confirmed to directly inhibit the lincomycin biosynthesis, whereas indirectly controlled the transcription of SLCG_2919, the first reported repressor in S. lincolnensis. Inactivation of SLCG_4846 in the high-yield S. lincolnensis LA219X (LA219XΔ4846) increases the Lin-A production and deletion of SLCG_2919 in LA219XΔ4846 exhibits superimposed yield increment. Given the effect of the double deletion on cellular primary metabolism of S. lincolnensis, Plackett-Burman design, steepest ascent and response surface methodologies were utilized and employed to optimize the seed medium of this double mutant in shake flask, and Lin-A yield using optimal seed medium was significantly increased over the control. Above strategies were performed in a 15-L fermenter. The maximal yield of Lin-A in LA219XΔ4846-2919 reached 6.56 g/L at 216 h, 55.1 % higher than that in LA219X at the parental cultivation (4.23 g/L). This study not only showcases the potential of this strategy to boost lincomycin production, but also could empower the development of high-performance actinomycetes for other antibiotics.

Efficient bio-production of glutaric acid by a metabolically engineered Escherichia coli LQ-1 based on a novel nitrogen source feeding strategy

As an important five-carbon platform chemical to synthesize polyesters and polyamides, glutaric acid is widely used in numerous biochemical fields such as consumer goods, textile, and footwear industries. However, the application of glutaric acid is limited by the low yield of its bio-production. In this study, a metabolically engineered Escherichia coli LQ-1 based on 5-aminovalerate (AMV) pathway was used for glutaric acid fed-batch fermentation. Given the significance of nitrogen source in the bio-production of glutaric acid by AMV pathway, a novel nitrogen source feeding strategy feedbacked by real-time physiological parameters was proposed after evaluating the effects of nitrogen source feeding (such as ammonia and ammonium sulfate) on glutaric acid bio-production. Under the proposed nitrogen source feeding strategy, a significantly improved glutaric acid production of 53.7 g L^-1 was achieved in a 30 L fed-batch fermentation by the metabolically engineered E. coli LQ-1, which was an improvement of 52.1% over pre-optimization. Additionally, a higher conversion rate of 0.64 mol mol^-1 (glutaric acid/glucose) was obtained compared with the previously reported bio-production of glutaric acid with E. coli. These results indicated that the nitrogen source feeding strategy proposed in this study will be useful for achieving the efficient and sustainable bio-based production of glutaric acid.

Identification of chitin synthase activator in Aspergillus niger and its application in citric acid fermentation

The biosynthesis of citric acid (CA) using Aspergillus niger as a carrier is influenced by mycelium morphology, which is determined by the expression level of morphology-related genes. As a key component of the fungal cell wall, chitin content has an important effect on morphogenesis, and to investigate the effects of this on fermentation performance, we used RNA interference to knockdown chitin synthase C (CHSC) and chitin synthase activator (CHS3) to obtain the single-gene mutant strains A. niger chs3 and chsC and the double mutant A. niger chs3C. We found that the CA fermentation performance of the two single mutants was significantly better than that of the double mutant. The mutant A. niger chs3-4 exhibited CA production potential compared to that of the parent strain in scale-up fermentation; we determined certain characteristics of CA high-yielding strain fermentation pellets. In addition, when chsC alone was silenced, there was very little change in chs3 mRNA levels, whereas those of chsC were significantly reduced when only chs3 was silenced. As this may be because of a synergistic effect between chsC and chs3, and we speculated that the latent activation target of CHS3 is CHSC, our results confirmed this hypothesis. This study is the first application of a separation and combination silence strategy of chitin synthase and chitin synthase activator in the morphology of A. niger CA fermentation. Furthermore, it provides new insights into the method for the morphological study of A. niger fermentation and the interaction of homologous genes. KEY POINTS: • The function of chitin synthase C (chsC) and chitin synthase activator (chs3) is tightly interrelated. • Mycelial morphology was optimized by knockdown of CHS3, resulting in the overproduction of citric acid. • The separation and combination silence strategies are promising tools for the interaction of homologous housekeeping genes.

Cofactor Engineering Redirects Secondary Metabolism and Enhances Erythromycin Production in Saccharopolyspora erythraea

Saccharopolyspora erythraea is used for industrial erythromycin production. To explore the physiological role of intracellular energy state in metabolic regulation by S. erythraea, we initially overexpressed the F₁ part of the endogenous F₁F₀-ATPase in the high yielding erythromycin producing strain E3. The F₁-ATPase expression resulted in lower [ATP]/[ADP] ratios, which was accompanied by a strong increase in the production of a reddish pigment and a decreased erythromycin production. Subsequent transcriptional analysis revealed that the lower intracellular [ATP]/[ADP] ratios exerted a pleotropic regulation on the metabolism of S. erythraea. The lower [ATP]/[ADP] ratios induced physiological changes to restore the energy balance, mainly via pathways that tend to produce ATP or regenerate NADH. The F₁-ATPase overexpression strain exhibited a state of redox stress, which was correlated to an alteration of electron transport at the branch of the terminal oxidases, and S. erythraea channeled the enhanced glycolytic flux toward a reddish pigment in order to reduce NADH formation. The production of erythromycin was decreased, which is in accordance with the net ATP requirement and the excess NADH formed through this pathway. Partial growth inhibition by apramycin increased the intracellular [ATP]/[ADP] ratios and demonstrated a positive correlation between [ATP]/[ADP] ratios and erythromycin synthesis. Finally, overexpression of the entire F₁F₀-ATPase complex resulted in 28% enhanced erythromycin production and markedly reduced pigment synthesis in E3. The work illustrates a feasible strategy to optimize the distribution of fluxes in secondary metabolism.

Biochemical engineering in China

Chinese biochemical engineering is committed to supporting the chemical and food industries, to advance science and technology frontiers, and to meet major demands of Chinese society and national economic development. This paper reviews the development of biochemical engineering, strategic deployment of these technologies by the government, industrial demand, research progress, and breakthroughs in key technologies in China. Furthermore, the outlook for future developments in biochemical engineering in China is also discussed.

An Online Respiratory Quotient-Feedback Strategy of Feeding Yeast Extract for Efficient Arachidonic Acid Production by Mortierella alpina

Mortierella alpina (M. alpina) is well known for arachidonic acid (ARA) production. However, low efficiency and unstableness are long existed problems for industrial production of ARA by M. alpina due to the lack of online regulations. The aim of the present work is to develop an online-regulation strategy for efficient and stable ARA production in industry. The strategy was developed in 50 L fermenters and then applied in a 200 m3 fermenter. Results indicated that yeast extract (YE) highly increased cell growth in shake flask, it was then used in bioreactor fermentation by various feeding strategies. Feeding YE to control respiratory quotient (RQ) at 1.1 during 0-48 h and at 1.5 during 48-160 h, dry cell weight, and ARA titer reached 53.1 and 11.49 g/L in 50 L fermenter, which were increased by 79.4 and 36.9% as compared to that without YE feeding, respectively. Then, the online RQ-feedback strategy was applied in 200 m3 bioreactor fermentation and an average ARA titer of 16.82 g/L was obtained from 12 batches, which was 41.0% higher than the control batches. This is the first report on successful application of online RQ-feedback control of YE in ARA production, especially in an industrial scale of 200 m3 fermentation. It could be applied to other industrial production of microbial oil by oleaginous microorganisms.

Integrated omics approaches provide strategies for rapid erythromycin yield increase in Saccharopolyspora erythraea

Background

Omics approaches have significantly increased our understanding of biological systems. However, they have had limited success in explaining the dramatically increased productivity of commercially important natural products by industrial high-producing strains, such as the erythromycin-producing actinomycete Saccharopolyspora erythraea. Further yield increase is of great importance but requires a better understanding of the underlying physiological processes.

Results

To reveal the mechanisms related to erythromycin yield increase, we have undertaken an integrated study of the genomic, transcriptomic, and proteomic differences between the wild type strain NRRL2338 (WT) and the industrial high-producing strain ABE1441 (HP) of S. erythraea at multiple time points of a simulated industrial bioprocess. 165 observed mutations lead to differences in gene expression profiles and protein abundance between the two strains, which were most prominent in the initial stages of erythromycin production. Enzymes involved in erythromycin biosynthesis, metabolism of branched chain amino acids and proteolysis were most strongly upregulated in the HP strain. Interestingly, genes related to TCA cycle and DNA-repair were downregulated. Additionally, comprehensive data analysis uncovered significant correlations in expression profiles of the erythromycin-biosynthetic genes, other biosynthetic gene clusters and previously unidentified putative regulatory genes. Based on this information, we demonstrated that overexpression of several genes involved in amino acid metabolism can contribute to increased yield of erythromycin, confirming the validity of our systems biology approach.

Conclusions

Our comprehensive omics approach, carried out in industrially relevant conditions, enabled the identification of key pathways affecting erythromycin yield and suggests strategies for rapid increase in the production of secondary metabolites in industrial environment.

Electronic supplementary material

The online version of this article (doi:10.1186/s12934-016-0496-5) contains supplementary material, which is available to authorized users.