Improvement of gibberellin production by a newly isolated Fusarium fujikuroi mutant

Bioprocess of Gibberellic Acid by Fusarium fujikuroi: The Challenge of Regulation, Raw Materials, and Product Yields

Gibberellic acid (GA3) is a tetracyclic diterpenoid carboxylic acid synthesized by the secondary metabolism of Fusarium fujikuroi. This phytohormone is widely studied due to the advantages it offers as a plant growth regulator, such as growth stimulation, senescence delay, flowering induction, increased fruit size, and defense against abiotic or biotic stress, which improve the quality and yield of crops. Therefore, GA3 has been considered as an innovative strategy to improve agricultural production. However, the yields obtained at large scale are insufficient for the current market demand. This low productivity is attributed to the lack of adequate parameters to optimize the fermentation process, as well as the complexity of its regulation. Therefore, this article describes the latest advances for potentializing the GA3 production process, including an analysis of its origins from crops, the benefits of its application, the related biosynthetic metabolism, the maximum yields achieved from production processes, and their association with genetic engineering techniques for GA3 producers. This work provides a new perspective on the critical points of the production process, in order to overcome the limits surrounding this modern line of bioengineering.

Establishment of a selectable marker recycling system for iterative gene editing in Fusarium fujikuroi

Gibberellic acid (GA3) is a vital plant growth hormone widely used in agriculture. Currently, GA3 production relies on liquid fermentation by the filamentous fungus Fusarium fujikuroi. However, the lack of an effective selection marker recycling system hampers the application of metabolic engineering technology in F. fujikuroi, as multiple-gene editing and positive-strain screening still rely on a limited number of antibiotics. In this study, we developed a strategy using pyr4-blaster and CRISPR/Cas9 tools for recycling orotidine-5'-phosphate decarboxylase (Pyr4) selection markers. We demonstrated the effectiveness of this method for iterative gene integration and large gene-cluster deletion. We also successfully improved GA3 titers by overexpressing geranylgeranyl pyrophosphate synthase and truncated 3-hydroxy-3-methyl glutaryl coenzyme A reductase, which rewired the GA3 biosynthesis pathway. These results highlight the efficiency of our established system in recycling selection markers during iterative gene editing events. Moreover, the selection marker recycling system lays the foundation for further research on metabolic engineering for GA3 industrial production.

Improving the productivity of gibberellic acid by combining small-molecule compounds-based targeting technology and transcriptomics analysis in Fusarium fujikuroi

Gibberellic acid (GA3), produced industrially by Fusarium fujikuroi, stands as a crucial plant growth regulator extensively employed in the agriculture filed while limited understanding of the global metabolic network hinders researchers from conducting rapid targeted modifications. In this study, a small-molecule compounds-based targeting technology was developed to increase GA3 production. Firstly, various small molecules were used to target key nodes of different pathways and the result displayed that supplement of terbinafine improved significantly GA3 accumulation, which reached to 1.08 g/L. Subsequently, lipid and squalene biosynthesis pathway were identified as the key pathways influencing GA3 biosynthesis by transcriptomic analysis. Thus, the strategies including in vivo metabolic engineering modification and in vitro supplementation of lipid substrates were adopted, both contributed to an enhanced GA3 yield. Finally, the engineered strain demonstrated the ability to achieve a GA3 yield of 3.24 g/L in 5 L bioreactor when utilizing WCO as carbon source and feed.

Understanding the Fermentation Potentiality For Gibberellic Acid (GA3) Production Using Fungi

Gibberellins represent an important group of potent phytohormones, growth-promoting, closely related diterpenoid acids biologically derived from tetracyclic diterpenoid hydrocarbon. Among these, gibberellic acid (GA3) has received the greatest attention. GA3 is a highly valued plant growth regulator which has various applications in agriculture. It is extensively used for beneficial effects including stem elongation, elimination of dormancy, sex expression, seed germination, flowering, and fruit senescence. Along with plants, many microbes are also producing GA3 as their secondary metabolite, and among these, fungi are reported to produce a higher amount of GA3. Fermentation technology based on submerged fermentation and solid-state fermentation for the production of GA3 has been used with its merits and demerits using Fusarium moniliforme fungus in the industry. Several mathematical models and optimization tools were also designed for enhancing the fermentative yield by researchers. The detailed analysis is essential to understand all the fermentation aspects, various unit parameters, process operation approaches, reduction in cost, and assessment of the possible uses of these models in the production of GA3 for higher yield. Recently, exclusive research is executed to lower down the production cost of GA3 approaching various strategies.

Optimization and reactor-scale production of plant growth regulators by Pleurotus eryngii

The aims of the this study are to select the best cultivation type for plant growth regulator (PGR) production, to optimize PGR production with statistical experimental design, and to calculate bioprocess parameters and yield factors during PGR production by P. eryngii in flask and reactor scales. Submerged fermentation was the best cultivation type with 4438.67 ± 37.14, 436.95 ± 27.31, and 54.32 ± 3.21 mg/L of GA3, ABA, and IAA production values, respectively. The Plackett-Burman and Box-Behnken designs were used to determine effective culture parameters and interactive effects of the selected culture parameters on PGR production by Pleurotus eryngii under submerged fermentation. The statistical model is valid for predicting PGR production by P. eryngii. After these studies, maximum PGR production (7926.17 ± 334.09, 634.92 ± 12.15, and 55.41 ± 4.38 mg/L for GA3, ABA, and IAA, respectively) was reached on the 18th day of fermentation under optimized conditions. The optimum formula was 50 g/L fructose, 3 g/L NaNO3, and 1.5 g/L KH2PO4, 1 mg/L thiamine, incubation temperature 25 °C, initial medium pH 7.0, and an agitation speed of 150 rpm. The kinetics of PGR production was investigated in batch cultivation under 3-L stirred tank reactor conditions. Concentrations of GA3, ABA, and IAA of 10,545.00 ± 527.25, 872.32 ± 21.81, and 60.48 ± 3.48 mg/L were obtained at the reactor scale which were 4.1, 3.4, and 2.3 times higher than the initial screening values. The specific growth rate (µ), the volumetric (rp) and specific (Qp) PGR production rates, 486.11 mg/L/day and 107.43 mg/g biomass/day for GA3, confirmed the successful transfer of optimized conditions to the reactor scale. In the presented study, PGR production of P. eryngii is reported for the first time.

Gibberellic acid overproduction in Fusarium fujikuroi using regulatory modification and transcription analysis

Gibberellic acid (GA₃), one of the natural diterpenoids produced by Fusarium fujikuroi, serves as an important phytohormone in agriculture for promoting plant growth. Presently, the metabolic engineering strategies for increasing the production of GA₃ are progressing slowly, which seriously restricted the advancing of the cost-effective industrial production of GA₃. In this study, an industrial strain with high-yield GA₃ of F. fujikuroi was constructed by metabolic modification, coupling with transcriptome analysis and promoter engineering. The over-expression of AreA and Lae1, two positive factors in the regulatory network, generated an initial producing strain with GA₃ production of 2.78 g L^-1. Compared with a large abundance of transcript enrichments in the GA₃ synthetic gene cluster discovered by the comparative transcriptome analysis, geranylgeranyl pyrophosphate synthase 2 (Ggs2), and cytochrome P450-3 genes, two key genes that respectively participated in the initial and final step of biosynthesis, were identified to be downregulated when the highest GA₃ productivity was obtained. Employing with a nitrogen-responsive bidirectional promoter, the two rate-limiting genes were dynamically upregulated, and therefore, the production of GA₃ was increased to 3.02 g L^-1. Furthermore, the top 20 upregulated genes were characterized in GA₃ over-production, and their distributions in chromosomes suggested potential genomic regions with a high transcriptional level for further strain development. The construction of a GA₃ high-yield-producing strain was successfully achieved, and insights into the enriched functional transcripts provided novel strain development targets of F. fujikuroi, offering an efficient microbial development platform for industrial GA₃ production. KEY POINTS: • Global regulatory modification was achieved in F. fujikuroi for GA₃ overproduction. • Comparative transcriptome analysis revealed bottlenecks in GA specific-pathway. • A dynamically nitrogen-regulated bidirectional promoter was cloned and employed.

Multivariate modular metabolic engineering for enhanced gibberellic acid biosynthesis in Fusarium fujikuroi

Gibberellic acid (GA3) is one of natural phytohormones, widely used in agriculture and downstream fields. Qualified for the nature productivity, Fusarium fujikuroi was currently employed for the industrial biotransformation from agriculture residues into GA3. Herein, Multivariate modular metabolic engineering (MMME) was assigned to reconstitute the metabolic balance in F. fujikuroi for enhancing GA3 production. Three modules including precursor pool, cluster-specific channel and P450-mediated oxidation in GA3 biosynthetic pathway were defined and optimized separately. The enhancement of both precursor pool and cluster-specific channel pushed metabolic flux transfer into the GA3-specific pathway. Moreover, both introduction of Vitreoscilla hemoglobin and reinforcement of NADPH-dependent cytochrome P450 reductase facilitated oxidation cofactor transfer and subsequently boosted mycelium growth and GA3 biosynthesis. Integration of three modules in the engineered strain accumulated 2.89 g/L GA3 in shake flask via submerged fermentation, presenting a promising modular metabolic engineering model for efficient microbial transformation in agro-industrial application.

RETRACTED ARTICLE: Mutagenesis combined with fermentation optimization to enhance gibberellic acid GA3 yield in Fusarium fujikuroi

Gibberellic acid (GA3) is a plant growth hormone that plays an important role in the production of crops, fruits, and vegetables with a wide market share. Due to intrinsic advantages, liquid fermentation of Fusarium fujikuroi has become the sole method for industrial GA3 production, but the broader application of GA3 is hindered by low titer. In this study, we combined atmospheric and room-temperature plasma (ARTP) with ketoconazole-based screening to obtain the mutant strain 3-6-1 with high yield of GA3. Subsequently, the medium composition and fermentation parameters were systematically optimized to increase the titer of GA3, resulting in a 2.5-fold increase compared with the titer obtained under the initial conditions. Finally, considering that the strain is prone to substrate inhibition and glucose repression, a new strategy of fed-batch fermentation was adopted to increase the titer of GA3 to 575.13 mg/L, which was 13.86% higher than the control. The strategy of random mutagenesis combined with selection and fermentation optimization developed in this study provides a basis for subsequent research on the industrial production of GA3.

Recent advances in metabolic regulation and bioengineering of gibberellic acid biosynthesis in Fusarium fujikuroi

The plant growth hormone gibberellic acid (GA₃), as one of the representative secondary metabolites, is widely used in agriculture, horticulture and brewing industry. GA₃ is detected in both plants and several fungi with the ability to stimulate plant growth. Currently, the main mode of industrial production of GA₃ is depended on the microbial fermentation via long-period submerged fermentation using Fusarium fujikuroi as the only producing strain, qualified for its natural productivity. However, the demand of large-sale industrialization of GA₃ was still restricted by the low productivity. The biosynthetic route of GA₃ in F. fujikuroi is now well-defined. Furthermore, the multi-level regulation mechanisms involved in the whole network of GA₃ production have also been gradually unveiled by the past two decades based on the identification and characterization of several global regulators and their mutual functions. Combined with the quick development of genetic manipulation techniques, the rational modification of producing strain F. fujikuroi development become practical for higher productivity achievement. Herein, we review the latest advances in the molecular regulation of GA₃ biosynthesis in F. fujikuroi and conclude a comprehensive network involving nitrogen depression, global regulator, histone modification and G protein signaling pathway. Correspondingly, the bioengineering strategies covering conventional random mutation, genetic manipulating platform development, metabolic edition and fermentation optimization were also systematically proposed.