Yian Gu

Alginate lyases depolymerize alginate via β-elimination and serve dual roles in brown-algal biorefining and antibiofilm therapy. Brown-algal and bacterial alginates differ substantially in O-acetylation, yet this key structural distinction and its implications for enzyme performance remain underappreciated. This review systematically integrates the complete causal chain from alginate polymer structure through enzyme recognition, catalytic mechanism, and protein engineering to bidirectional applications. We cover PL family classification, the structural basis of substrate specificity, engineering strategies including two-step activity stability optimization and AI-assisted design, and recent progress in tailored alginate oligosaccharide preparation and cystic fibrosis treatment. Our central analysis identifies a widespread substrate mismatch, as most enzymological characterization relies on non-acetylated sodium alginate, whereas the clinical target is heavily acetylated bacterial alginate. This review establishes acetylated substrate adaptation as the critical gap between fundamental enzymology and medical translation and outlines future directions including multi-objective optimization and AI-driven enzyme design.

Soil salinization poses an escalating threat to global crop production. Extracellular polysaccharides (EPSs) secreted by plant growth-promoting rhizobacteria have the potential to improve the salt tolerance of crops. Here, we tested the effects of Pantoea alhagi NX-11 EPSs on the growth, physiological traits, and root proteomic profiles of rice under salt stress. We found that NX-11 EPSs effectively increased the salt tolerance of rice in soil, with 50 mg/kg EPS exhibiting the strongest plant growth-promoting effect. This effect was associated with increased the K⁺/Na⁺ ratio and soluble protein content in roots induced by NX-11 EPSs as well as reduced stomatal aperture and transpiration rate in leaves. Proteomic analyses revealed that NX-11 EPSs markedly changed the protein profiles of roots. Specifically, proteins associated with cyanoamino acid metabolism, glycolysis/gluconeogenesis, and fatty acid degradation were downregulated. Together, these results suggest that NX-11 EPSs improve rice performance under salt stress, accompanied by changes in physiological traits and root protein profiles.

Rhamnolipids (RLs) are natural biosurfactants produced by microbial fermentation. They exhibit excellent surface activity, environmental compatibility, and versatile biological activities, with broad application potential in energy development, environmental remediation, personal care, and biomedicine. In recent years, RLs have garnered significant attention due to the structural divergence between mono-rhamnolipids (mono-RLs) and di-rhamnolipids (di-RLs). Their distinct physicochemical and biological properties necessitate structure-function-guided “tailor-made” synthesis. Notably, the compositional fluctuation of naturally occurring RL mixtures constrains their high-value utilization. This review systematically summarizes the structure–function relationships, microbial biosynthetic pathways, and regulatory approaches of mono-RLs and di-RLs, with a core focus on the targeted production of RLs with specific mono-/di-RL ratios. The review also highlights the application-specific suitability of the two RL congeners. It aims to provide a theoretical foundation and technical reference for the precision manufacturing and commercialization of RLs in energy, environment, health, and other related fields.

Ultraviolet (UV) radiation is a primary driver of skin photoaging, characterized by oxidative stress, persistent inflammatory responses, and excessive degradation of the extracellular matrix (ECM). Naematelia aurantialba is a traditional medicinal and edible fungus recognized for its diverse pharmacological activities. In this study, N. aurantialba polysaccharides (NAPS-A)—high-value bioactive compounds obtained through liquid fermentation—were subjected to detailed functional characterization to evaluate their restorative potential against UVB-induced damage. The results demonstrated that NAPS-A treatment effectively mitigated UVB-induced cytotoxicity. Furthermore, NAPS-A significantly suppressed the accumulation of reactive oxygen species (ROS) and malondialdehyde (MDA), while robustly revitalizing the endogenous antioxidant defense system by restoring superoxide dismutase (SOD) and catalase (CAT) activities. Moreover, NAPS-A exerted potent anti-inflammatory effects by inhibiting the secretion of nitric oxide (NO) and pro-inflammatory cytokines, including IL-1β, IL-6, and TNF-α. NAPS-A maintained ECM homeostasis by counteracting collagen depletion, exhibiting inhibitory activity against collagenase and elastase, and modulating the mRNA expression of Col1a1 and Col3a1. These findings suggested that NAPS-A protects fibroblasts from UVB-induced damage through a synergistic mechanism involving radical scavenging, the enhancement of cellular redox homeostasis, and the modulation of ECM metabolism. Overall, NAPS-A represents a promising, sustainably produced, food-derived bioactive ingredient with significant potential for the development of functional foods and nutricosmetics aimed at mitigating UVB-induced skin damage.

Non-spore-forming bacteria exhibit remarkable species diversity and sophisticated salt-resistance mechanisms, making them predominant candidates for commercial microbial inoculants worldwide. However, their low viability during storage and field application has severely constrained utilization. Inspired by the robust structure of spore dormancy, we propose a novel core-shell microcapsule (APC). Using Pantoea alhagi NX-11 as a model, APC encapsulation improved viability from 2.95 to 8.43 log CFU/g after 12-week storage at room temperature. The survival mechanism is attributed to APC-induced metabolic dormancy via suppression of the TCA cycle and oxidative phosphorylation pathways. Notably, compared to non-encapsulated NX-11, inoculation of APC-encapsulated NX-11 increased rice root dry weight by 24.61% under salt stress in greenhouse experiments and altered rhizosphere bacterial community structure. NX-11 showed higher relative abundance in rhizospheres treated with APC-encapsulated NX-11. Universality was validated in two additional non-spore bacterial strains. These results demonstrate APC’s efficacy in preserving non-spore microbial inoculants and enhancing plant salt stress tolerance, highlighting a novel approach for microbial formulation development.

Despite the critical role rhizosphere microbiomes play in plant growth, manipulating microbial communities for improved plant productivity remains challenging. One reason for this is the lack of knowledge on how complex substrates secreted in the microbiome ultimately shape the microbe-microbe and plant-microbe interaction in relation to plant growth. One such complex substrate is poly-γ-glutamic acid, which is a microbially derived extracellular polymer. While it has previously been linked with plant growth-promotion, the underlying mechanisms are not well understood. Here we show that this compound benefits plants by fostering cross-feeding networks between rhizosphere bacteria. We first experimentally demonstrate that poly-γ-glutamic acid application increases potassium bioavailability for tomato plants by driving a shift in the rhizosphere bacterial community composition. Specifically, application of poly-γ-glutamic acid increased the relative abundance of Pseudomonas nitroreducens L16 and Pseudomonas monteilii L20 bacteria which both promoted tomato potassium assimilation by secreting potassium-solubilizing pyruvic acid and potassium-chelating siderophores, respectively. Although either Pseudomonas strain could not metabolize poly-γ-glutamic acid directly, the application of poly-γ-glutamic acid promoted the growth of Bacillus species, which in turn produced metabolites that could promote the growth of both P. nitroreducens L16 and P. monteilii L20. Moreover, the P. monteilii L20 produced 3-hydroxycapric acid, which could promote the growth of P. nitroreducens L16, resulting in commensal cross-feeding interaction between plant growth-promoting bacteria. Together, these results show that poly-γ-glutamic acid plays a crucial role in driving plant growth-promotion via bacterial cross-feeding networks, highlighting the opportunity for using microbially derived, complex substrates as catalysts to increase agricultural productivity.