Enhanced Biosynthesis of D-Arabitol by Metschnikowia reukaufii Through Optimizing Medium Composition and Fermentation Conditions

Fine-tuning the pathway and fermentation conditions to explore Pichia pastoris for high-level d-arabitol production from glucose

The bioproduction of d-arabitol has recently attracted considerable attention due to its potential applications in the food, chemical, and pharmaceutical industries. However, current technologies, primarily employing unconventional osmotolerant yeasts and traditional strain-improvement strategies, face challenges such as low conversion efficiency, instability, and limited industrial adaptability. Thus, developing robust chassis through precise rational metabolic engineering is essential for enhancing the overall efficiency and sustainability of this bioproduction process. In this regard, Pichia pastoris, a widely used host for heterologous protein production, was systematically and rationally engineered in this study by overexpressing key metabolic enzymes involved in d-arabitol biosynthesis and fine-tuning promoters and gene copy numbers. Through this metabolic re-modulation and subsequent bioprocess optimization, a final d-arabitol titer of 78.1 g/L was achieved during fed-batch fermentation in a bioreactor. These findings underscore the significant potential of employing P. pastoris as a new and robust chassis for advancing d-arabitol biosynthesis.

Optimal fermentation of Pseudomonas synxantha M1 and metabolomics analysis

The microbial agents based on plant growth promoting rhizobacteria (PGPR) have become a hot topic in agricultural research, while the optimization of fermentation conditions for PGPR-based microbial agents still lack systematic research. The single-factor and orthogonal experiments were conducted to determine the optimal fermentation conditions of Pseudomonas synxantha M1. The results indicated that the glycerol and shaker speed was the most significant factors that influence the number of bacteria of P. synxantha M1 fermentation liquid. The viable bacteria count of microbial agent reached 7.1 × 1012 cfu/mL at 36 h, which OD600 value increased by 116.40% compared to before optimization, and promote the growth of highland barley. Significant differences of metabolites of fermentation liquid was observed in different fermentation times, including organic acids, lipids, and organoheterocyclic compounds using liquid chromatography tandem mass spectrometry (LC-MS/MS). In addition, the fermentation liquid was found to contain indoleacetic acid, glutathione and xanthine at the end of fermentation, which might contribute for the growth of plants as bioactive substances.

Stress-Driven Production of γ-Aminobutyric Acid Using Non-Conventional Yeast Strains Kluyveromyces marxianus JMY140K and Metschnikowia reukaufii JMY075

γ-Aminobutyric acid (GABA) is a valuable amino acid widely used in food, healthcare, and agriculture. GABA bioproduction by budding yeasts has been commonly reported, but related studies using non-conventional yeasts remain limited. In this study, two non-conventional natural yeast strains, namely, Kluyveromyces marxianus JMY140K and Metschnikowia reukaufii JMY075, were identified as promising GABA producers, and M. reukaufii JMY075 was discovered to be a GABA producer. Enhanced GABA production was observed in the two yeast strains under stress conditions, including high temperature and high ethanol and acetic acid levels. In particular, K. marxianus JMY140K showed 7.93 times higher GABA titers under thermal stress than that of the control. External stress conditions significantly influenced the GABA production of these two yeast strains. The culture filtrate of K. marxianus JMY140K also showed promising activities in human skin cells. In addition, K. marxianus JMY140K could also produce GABA using rice straw hydrolysate, which indicated that it has the potential to produce GABA using renewable biomass. Our studies provide insight for further enhancing the GABA production of natural yeasts and promoting its biotechnology applications.

Research progress in the biosynthesis of xylitol: feedstock evolution from xylose to glucose

Xylitol, as an important food additive and fine chemical, has a wide range of applications, including food, medicine, chemical, and feed. This review paper focuses on the research progress of xylitol biosynthesis, from overcoming the limitations of traditional chemical hydrogenation and xylose bioconversion, to the full biosynthesis of xylitol production using green and non-polluting glucose as substrate. In the review, the molecular strategies of wild strains to increase xylitol yield, as well as the optimization strategies and metabolic reconfiguration during xylitol biosynthesis are discussed. Subsequently, on the basis of existing studies, the paper further discusses the current status of research and future perspectives of xylitol production using glucose as a single substrate. The evolution of raw materials from xylose-based five-carbon sugars to glucose is not only cost-saving, but also safe and environmentally friendly, which brings new opportunities for the green industrial chain of xylitol.

Sustainable bio-manufacturing of D-arabitol through combinatorial engineering of Zygosaccharomyces rouxii, bioprocess optimization and downstream separation

Biosynthesis of D-arabitol, a high value-added platform chemical, from renewable carbon sources provides a sustainable and eco-friendly alternative to the chemical industry. Here, a robust brewing yeast, Zygosaccharomyces rouxii, capable of naturally producing D-arabitol was rewired through genome sequencing-based metabolic engineering. The recombinant Z. rouxii obtained by reinforcing the native D-xylulose pathway, improving reductive power of the rate-limiting step, and inhibiting the shunt pathway, produced 73.61% higher D-arabitol than the parent strain. Subsequently, optimization of the fermentation medium composition for the engineered strain provided 137.36 g/L D-arabitol, with a productivity of 0.64 g/L/h in a fed-batch experiment. Finally, the downstream separation of D-arabitol from the complex fermentation broth using an ethanol precipitation method provided a purity of 96.53%. This study highlights the importance of D-xylulose pathway modification in D-arabitol biosynthesis, and pave a complete and efficient way for the sustainable manufacturing of this value-added compound from biosynthesis to preparation.

High-level production of d-arabitol by Zygosaccharomyces rouxii from glucose: Metabolic engineering and process optimization

d-Arabitol is a top value-added compound with wide applications in the food, pharmaceutical and biochemical industries. Nevertheless, sustainable biosynthesis of d-arabitol is limited by lack of efficient strains and suitable fermentation process. Herein, metabolic engineering and process optimization were performed in Zygosaccharomyces rouxii to overcoming these limitations. Adopting systems metabolic engineering include enhancement of innate biosynthetic pathway, supply of precursor substrate d-ribulose-5P and cofactors regeneration, a novel recombinant strain ZR-5A with good performance was obtained, which boosted d-arabitol production up to 29.01 g/L, 59.31 % higher than the parent strain. Further with the optimum medium composition and fed-batch fermentation, the strain ZR-5A finally produced 149.10 g/L d-arabitol with the productivity of 1.04 g/L/h, which was the highest titer ever reported by Z.rouxii system. This is the first report on the use of metabolic engineering to construct Z. rouxii chassis for the sustainable production of d-arabitol.

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.