Fan Yang

Oligosaccharides are plant immune elicitors with recognized roles in seed germination, root development and stress regulation. However, most studies have focused on single oligosaccharides or the independent effects of rhizosphere microorganisms. The coordinated regulation of plant physiological networks and microbial communities by oligosaccharide-based seed coatings remains poorly understood, especially for xanthan oligosaccharides. Here, using wheat root transcriptomics, rhizosphere 16S rRNA sequencing, and physiological assays, we found that a xanthan oligosaccharide composite seed coating significantly improved germination potential, germination rate and seedling vigor. It promoted root and shoot growth under field conditions, optimized the balance of auxin, gibberellin and abscisic acid, activated endosperm hydrolytic enzymes and accelerated nutrient mobilization. Transcriptomics revealed stage-specific regulation of membrane lipid metabolism, hormone signaling, antioxidant defense, carbon/nitrogen metabolism and ABC transporters. Microbiome analysis showed selective enrichment of beneficial genera (Devosia, Paenarthrobacter, Citricoccus), which were positively associated with root nitrogen metabolism and MAPK signaling. Collectively, the coating promoted wheat growth and was associated with stress-related physiological and molecular responses; however, direct stress-challenge and functional-validation experiments are required to verify stress-tolerance mechanisms.

Exploring the microbial catabolism of complex polysaccharides like xanthan (XG) is crucial for improving oligosaccharide production and their use in food and agriculture. Through mutagenesis, we obtained a mutant bacterium, Microbacterium sp. YXT11, which rapidly utilizes XG and efficiently accumulates oligoxanthan (XOG). Further process optimization led to an 8.67-fold increase in XOG productivity. Additionally, XOG exhibited a narrow polydispersity, along with enhanced antioxidant (IC₅₀ = 1.25 mg/mL for hydroxyl radical scavenging) and immunomodulatory properties (effective at 25 μg/mL). Furthermore, the mechanism underlying the efficient XG catabolism in YXT11 was elucidated, involving the downregulation of the flagellar assembly pathway for metabolic adjustment and the switching of the xanthan catabolic pathway from the repressed XG-specific PUL to a pathway containing CAZymes with similar functions as well as the upregulation of the mannitol-specific phosphotransferase system. These findings deepen our understanding of xanthan catabolism and provide a molecular basis for its efficient degradation, aiding its practical valorization.

Isomaltulose, a sucrose isomer with a low glycemic index and non-cariogenic properties, is extensively used in the food industry. The industrial production of this functional sugar relies on enzymatic biotransformation using sucrose isomerase (SIase). However, conventional bioprocesses involve expressing and isolating the SIase enzyme, followed by using the purified SIase to convert sucrose into isomaltulose, resulting in a multi-step and high-cost process that hindered the broader applications of isomaltulose. In this study, we reported a streamlined one-step bioprocess that integrates extracellular SIase secretion and direct isomaltulose biosynthesis in the culture medium of an engineered B. subtilis strain. Using CRISPR/Cas9 technology, we engineered B. subtilis to integrate multiple SIase expression cassettes into the genome while concurrently replacing genes within the sacP-sacA-ywdA and sacB-levB-yveA operons, which are crucial for sucrose hydrolysis in B. subtilis. This strategy synergistically increased the genomic copy number of SIase gene while limited sucrose consumption by native pathways, thereby maximizing substrate availability for SIase-mediated catalysis. The resulting engineered strain, containing four copies of the SIase expression cassettes, achieved an extracellular SIase activity of 8.2 U/mL in shake flasks. When cultured in a medium containing 200 g/L sucrose, this strain produced a maximum isomaltulose titer of 162.1 g/L with a yield of 0.81 g/g and a productivity of 13.5 g/L/h. These findings demonstrate an integrated bioprocess that eliminates costly enzyme isolation procedure and reduces fermentation complexity, presenting a commercially feasible strategy for sustainable isomaltulose production.

The inherently high viscosity of xanthan has constrained its utility as a dietary fiber in various applications. In this study, a novel enzymatic strategy was established by employing two thermostable xanthanases (Xan12E and XanVA) to generate low-viscosity xanthan derivatives. Structural and molecular dynamics analyses revealed Xan12E's superior thermal resilience (no melting temperature ≤ 95 °C) and lower conformational fluctuations compared to XanVA. Under high temperatures, Xan12E exhibited a catalytic activity of 247.1 U g^-1, representing a 1.5-fold increase compared to XanVA. Enzymolysis using Xan12E resulted in a 19.7-fold reduction in viscosity, accompanied by a substantial decrease in the molecular weight from 3.4 × 10⁶ to 1.0 × 10⁵ Da while retaining the key functional groups essential for xanthan's bioactivity. The enzymatically modified xanthan exhibited notable antioxidant activity with IC₅₀ values ranging from 0.5 to 5.8 g L^-1. Furthermore, it exerted pronounced anti-inflammatory effects in macrophages, suppressing the expression of COX-2, TNF-α, IL-1β, iNOS, and IL-6 at 100 μg mL^-1. This study establishes high-temperature enzymolysis using Xan12E as a scalable, eco-friendly method to produce low-viscosity xanthan with enhanced bioactivity, addressing a critical gap in functional food additives and expanding xanthan's applications in the food industry.

Lignocellulose bio-refinery via microbial cell factories for chemical production represents a renewable and sustainable route in response to resource starvation and environmental concerns. However, the challenges associated with the co-utilization of xylose and glucose often hinders the efficiency of lignocellulose bioconversion. Here, we engineered yeast Ogataea polymorpha to effectively produce free fatty acids from lignocellulose. The non-oxidative branch of the pentose phosphate pathway, and the adaptive expression levels of xylose metabolic pathway genes XYL1, XYL2 and XYL3, were systematically optimized. In addition, the introduction of xylose transporter and global regulation of transcription factors achieved synchronous co-utilization of glucose and xylose. The engineered strain produced 11.2 g/L FFAs from lignocellulose hydrolysates, with a yield of up to 0.054 g/g. This study demonstrated that metabolic rewiring of xylose metabolism could support the efficient co-utilization of glucose and xylose from lignocellulosic resources, which may provide theoretical reference for lignocellulose biorefinery.

Astaxanthin, a carotenoid endowed with potent antioxidant capacity, exhibits considerable application prospects in nutraceuticals, pharmaceuticals, and cosmetics. In contrast to the chemical synthesis method, the biosynthesis of astaxanthin is undoubtedly a greener and more environmentally friendly production approach. In this review, we comprehensively review the biosynthetic pathways and multiple strategies for astaxanthin synthesis in Phaffia rhodozyma. Some biotechnology advancements for increasing the yield of astaxanthin in Phaffia rhodozyma encompass mutagenesis breeding, genetic modification, and optimizing fermentation conditions, thereby opening up new avenues for its application in functional foods and feed. Nevertheless, the yield of product synthesis is constrained by the host metabolic stoichiometry. Besides breaking the threshold of astaxanthin production and alleviating the impact of astaxanthin accumulation on cell growth, a comprehensive comprehension of multiple interconnected metabolic pathways and complex regulatory mechanisms is indispensable for significantly enhancing astaxanthin production. This review presents some prospects of integrating digital concepts into astaxanthin production to aid in overcoming current challenges.