Exploring differential traits of lipid-producing stages of the wild type and morphologically engineered strain of Aspergillus oryzae by comparative kinetic modeling

Development of Aspergillus oryzae BCC7051 as a Robust Cell Factory Towards the Transcriptional Regulation of Protease-Encoding Genes for Industrial Applications

Enzyme-mediated protein degradation is a major concern in industrial fungal strain improvement, making low-proteolytic strains preferable for enhanced protein production. Here, we improved food-grade Aspergillus oryzae BCC7051 by manipulating the transcriptional regulation of protease-encoding genes. Genome mining of the transcription factor AoprtR and computational analysis confirmed its deduced amino acid sequence sharing evolutionary conservation across Aspergillus and Penicillium spp. The AoPrtR protein, which is classified into the Zn(II)2-Cys6-type transcription factor family, manipulates both intra- and extracellular proteolytic enzymes. Our transcriptional analysis indicated that the regulation of several protease-encoding genes was AoPrtR-dependent, with AoPrtR acting as a potent activator for extracellular acid-protease-encoding genes and a likely repressor for intracellular non-acid-protease-encoding genes. An indirect regulatory mechanism independent of PrtR may enhance proteolysis. Moreover, AoPrtR disruption increased extracellular esterase production by 2.55-fold, emphasizing its role in protein secretion. Our findings highlight the complexity of AoPrtR-mediated regulation by A. oryzae. Manipulation of regulatory processes through AoPrtR prevents secreted protein degradation and enhances the quantity of extracellular proteins, suggesting the low-proteolytic variant as a promising platform for the production of these proteins. This modified strain has biotechnological potential for further refinement and sustainable production of bio-based products in the food, feed, and nutraceutical industries.

Lipid production by robust Aspergillus oryzae BCC7051 and a mathematical model describing its growth and lipid phenotypic traits

AIMS

To identify the promising oleaginous Aspergillus oryzae strain and leverage its lipid and biomass production through a mathematical model.

METHODS AND RESULTS

Comparative profiling of the cell growth and total fatty acid (TFA) content among 13 strains of A. oryzae was performed to explore the discrimination in their lipid productions. The oleaginicity of A. oryzae was found to be strain dependent, where the fungal strain BCC7051 exhibited superior performance in producing lipid-rich biomass by submerged fermentation. The TFA contents of the strain BCC7051 were comparable when cultivated at a range of pH values (pH 3.5-6.5) and temperatures (24-42°C). The mathematical model was generated, well describing and predicting the fungal growth and lipid phenotypic traits at various temperatures and carbon substrates.

CONCLUSION

The A. oryzae strain BCC7051 was a robust cell factory, acquiring economically feasible options for producing valuable lipid-based products.

Efficient de novo production of bioactive cordycepin by Aspergillus oryzae using a food-grade expression platform

BACKGROUND

Cordycepin (3'-deoxyadenosine) is an important bioactive compound in medical and healthcare markets. The drawbacks of commercial cordycepin production using Cordyceps spp. include long cultivation periods and low cordycepin yields. To overcome these limitations and meet the increasing market demand, the efficient production of cordycepin by the GRAS-status Aspergillus oryzae strain using a synthetic biology approach was developed in this study.

RESULTS

An engineered strain of A. oryzae capable of cordycepin production was successfully constructed by overexpressing two metabolic genes (cns1 and cns2) involved in cordycepin biosynthesis under the control of constitutive promoters. Investigation of the flexibility of carbon utilization for cordycepin production by the engineered A. oryzae strain revealed that it was able to utilize C6-, C5-, and C12-sugars as carbon sources, with glucose being the best carbon source for cordycepin production. High cordycepin productivity (564.64 ± 9.59 mg/L/d) was acquired by optimizing the submerged fermentation conditions.

CONCLUSIONS

This study demonstrates a powerful production platform for bioactive cordycepin production by A. oryzae using a synthetic biology approach. An efficient and cost-effective fermentation process for cordycepin production using an engineered strain was established, offering a powerful alternative source for further upscaling.

Transcriptome-based Mining of the Constitutive Promoters for Tuning Gene Expression in Aspergillus oryzae

Transcriptional regulation has been adopted for developing metabolic engineering tools. The regulatory promoter is a crucial genetic element for strain optimization. In this study, a gene set of Aspergillus oryzae with highly constitutive expression across different growth stages was identified through transcriptome data analysis. The candidate promoters were functionally characterized in A. oryzae by transcriptional control of β-glucuronidase (GUS) as a reporter. The results showed that the glyceraldehyde triphosphate dehydrogenase promoter (PgpdA1) of A. oryzae with a unique structure displayed the most robust strength in constitutively controlling the expression compared to the PgpdA2 and other putative promoters tested. In addition, the ubiquitin promoter (Pubi) of A. oryzae exhibited a moderate expression strength. The deletion analysis revealed that the 5' untranslated regions of gpdA1 and ubi with the length of 1028 and 811 nucleotides, counted from the putative translation start site (ATG), respectively, could efficiently drive the GUS expression. Interestingly, both promoters could function on various carbon sources for cell growth. Glucose was the best fermentable carbon source for allocating high constitutive expressions during cell growth, and the high concentrations (6-8% glucose, w/v) did not repress their functions. It was also demonstrated that the secondary metabolite gene coding for indigoidine could express under the control of PgpdA1 or Pubi promoter. These strong and moderate promoters of A. oryzae provided beneficial options in tuning the transcriptional expression for leveraging the metabolic control towards the targeted products.

Metabolic Regulation of Sugar Assimilation for Lipid Production in Aspergillus oryzae BCC7051 through Comparative Transcriptome Perspective

Simple Summary

Oleaginous fungi are a promising candidate to produce microbial lipids as alternative sources for industrial applications. As lipids are intracellular metabolites with dynamic traits, the fungal ability in utilizing carbon sources for biomass and lipid production is significant in terms of production yield and economic feasibility. This study aimed to explore the metabolic regulation in lipogenesis of oleaginous Aspergillus oryzae BCC7051 at the transcriptional level. Through comparative transcriptome analysis, a set of differentially expressed genes (DEGs) between the xylose- and glucose-grown cultures (C5 and C6 cultures) at fast-growing and lipid-accumulating stages were identified and functionally categorized into transporter proteins and cellular processes. Combining with the growth and lipid phenotypes, the transcriptome results pointed to a crucial link between sugar assimilation, energy, lipid, and other metabolisms in A. oryzae for leveraging the metabolic flux from xylose to fatty acid and lipid biosynthesis in render the oleaginous features. This study provides a remarkable insight in guiding strain optimization and bioprocess development using renewable feedstocks from agroindustrial residues.

Abstract

Microbial lipid production with cost effectiveness is a prerequisite for the oleochemical sector. In this work, genome-wide transcriptional responses on the utilization of xylose and glucose in oleaginous Aspergillus oryzae were studied with relation to growth and lipid phenotypic traits. Comparative analysis of the active growth (t1) and lipid-accumulating (t2) stages showed that the C5 cultures efficiently consumed carbon sources for biomass and lipid production comparable to the C6 cultures. By pairwise comparison, 599 and 917 differentially expressed genes (DEGs) were identified in the t1 and t2 groups, respectively, in which the consensus DEGs were categorized into polysaccharide-degrading enzymes, membrane transports, and cellular processes. A discrimination in transcriptional responses of DEGs set was also found in various metabolic genes, mostly in carbohydrate, amino acid, lipid, cofactors, and vitamin metabolisms. Although central carbohydrate metabolism was shared among the C5 and C6 cultures, the metabolic functions in acetyl-CoA and NADPH generation, and biosynthesis of terpenoid backbone, fatty acid, sterol, and amino acids were allocated for leveraging biomass and lipid production through at least transcriptional control. This study revealed robust metabolic networks in the oleaginicity of A. oryzae governing glucose/xylose flux toward lipid biosynthesis that provides meaningful hints for further process developments of microbial lipid production using cellulosic sugar feedstocks.

Significance of two intracellular triacylglycerol lipases of Aspergillus oryzae in lipid mobilization: A perspective in industrial implication for microbial lipid production

Microbial lipid production of oleaginous strains involves in a complex cellular metabolism controlling lipid biosynthesis, accumulation and degradation. Particular storage lipid, triacylglycerol (TAG), contributes to dynamic traits of intracellular lipids and cell growth. To explore a basis of TAG degradation in the oleaginous strain of Aspergillus oryzae, the functional role of two intracellular triacylglycerol lipases, AoTgla and AoTglb, were investigated by targeted gene disruption using CRISPR/Cas9 system. Comparative lipid profiling of different cultivation stages between the control, single and double disruptant strains (ΔAotgla, ΔAotglb and ΔAotglaΔAotglb strains) showed that the inactivation of either AoTgla or AoTglb led to the increase of total lipid contents, particularly in the TAG fraction. Moreover, the prolonged lipid-accumulating stage of all disruptant strains was obtained as indicated by a reduction in specific rate of lipid turnover, in which a holding capacity in maximal lipid and TAG levels was achieved. The involvement of AoTgls in spore production of A. oryzae was also discovered. In addition to the significance in lipid physiology of the oleaginous fungi, this study provides an impact on industrial practice by overcoming the limitation in short lipid-accumulating stage of the fungal strain, which facilitate the cell harvesting step at the maximum lipid production yield.