Chongqing University of Arts & Sciences

This study identified Lactiplantibacillus plantarum SS0831 (LP) as a high-performing strain in suansun and investigated its impact on flavor quality through comprehensive analyses of flavor compounds, microbial succession, functional dynamics, and metabolic pathways. Compared with naturally fermented suansun (NFS), Lactiplantibacillus plantarum-inoculated fermented suansun (LPIFS) exhibited higher acidity and improved sensory scores. LPIFS contained 63 aroma compounds, significantly more than the 41 detected in NFS. Notably, p-cresol levels in LPIFS decreased by over 50 % within the first seven days of fermentation, while alcohols, esters, and aldehydes increased, enriching the overall flavor profile. It additionally uncovered a notable positive correlation involving Lactococcus in conjunction with p-cresol, 2-nonenal, and phenylethanol. During early fermentation, Proteobacteria played a crucial role in flavor formation. The microbial community in LPIFS demonstrated enhanced carbohydrate metabolism. Particularly noteworthy is that LPIFS enhances flavor through a dual strategy-reducing the formation of acidic off-flavors while increasing aromatic compounds. The positive correlation between Lactococcus and p-cresol sheds light on the underlying mechanism of aroma enhancement. By facilitating more moderate cooperative interactions among the microbial communities in LPIFS, galactose, butanoate, and tyrosine metabolisms may be altered, while tryptophan metabolism may be modified, leading to reduced p-cresol production. Moreover, enhanced pyruvate metabolism was also a key factor in the synthesis of increased aroma compounds. These findings provide new insights into suansun flavor enhancement and the metabolic mechanisms driving its improvement.

The development of highly active and durable carbon-based electrocatalysts for the oxygen reduction reaction (ORR) is of critical importance. In this study, a heteroatom-doped carbon catalyst (FeSn-NFC) was synthesized through the chelation of Fe³⁺ and dopamine hydrochloride, followed by Sn/F co-doping and carbonization. The resulting FeSn-NFC catalyst exhibits an ultrahigh specific surface area of 2387.9 m² g^-1, with micropores accounting for 79 % of its structure. The incorporation of Sn enhances the pyridinic nitrogen content and facilitates the elimination of reactive oxygen species (ROS). Electrochemical evaluations reveal exceptional ORR performance, with a half-wave potential (E_1/2) of 0.857 V and a minimal degradation (ΔE_1/2 = 11 mV) after accelerated aging tests. When integrated into a zinc-air battery, the FeSn-NFC catalyst delivers a peak power density of 217 mW cm^-2 and an energy density of 880 Wh kg^-1 (Zn), maintaining 93.2 % of its initial energy density after ∼115 h of continuous operation. This work offers a novel strategy for fabricating efficient, stable, and cost-effective ORR electrocatalysts, advancing the field of energy conversion technologies.

The root-associated methanotrophs contribute to N₂ fixation and CH₄ oxidation in paddy fields under N-limited conditions. However, the impact of nitrogen inputs on N₂ fixation and CH₄ oxidation by methanotrophs is largely unknown, especially in saline-alkali paddy fields with higher nitrogen application. This study explored the impact of nitrogen fertilization on N₂ fixation and CH₄ oxidation by root-associated active diazotrophic and methanotrophic communities in a saline-alkali paddy field using ¹⁵N-N₂ and ¹³C-CH₄ isotope feeding experiments along with RNA-based sequencing. The ¹⁵N and ¹³C isotope feeding experiments showed that the CH₄ oxidation-dependent nitrogen fixation rate of methanotrophs (¹⁵N and ¹³C) in the roots of two rice cultivars was significantly higher than the CH₄ oxidation-independent nitrogen fixation rate of heterotrophic diazotrophs (only ¹⁵N) under nitrogen fertilization (SN) in a saline-alkali environment (P < 0.05). For Kongyu131 rice, the CH₄ oxidation-dependent nitrogen fixation rate ranged from 1.17 to 4.15 μmol/h/g, while the CH₄ oxidation-independent nitrogen fixation rate was determined to be 1.10 to 3.17 μmol/h/g. In J3 rice, these rates were 7.30 to 9.22 μmol/h/g and 5.76 to 4.85 μmol/h/g, respectively (P < 0.05). Moreover, both N₂ fixation and CH₄ oxidation rates of methanotrophs in the roots of salt-alkali tolerant J3 cultivar (9.22 μmol/h/g for N₂ fixation; 0.09 μmol/h/g for CH₄ oxidation) were significantly higher than those in the roots of the common rice cultivar Kongyu131 (4.15 μmol/h/g for N₂ fixation; 0.03 μmol/h/g for CH₄ oxidation) under nitrogen fertilization (P < 0.01). Thus, methanotrophs associated with J3 rice roots demonstrated improved N₂ fixation and CH₄ oxidation activities under saline-alkali stress in the presence of nitrogen fertilizer. Even heterotrophic diazotrophs in J3 rice roots showed enhanced N₂ fixation with (SN) or without (LN) nitrogen inputs. The RNA-based amplicon sequencing showed that nitrogen fertilizer had a greater influence on diazotrophic and methanotrophic communities than the differences between rice cultivars. Further, active Methylomonas (type I methanotrophs) dominated the root-associated diazotrophic (9.8-20.9%) and methanotrophic (46.8-80.3%) communities. Within these, Methylomonas methanica (13.3 vs. 3.8%) and Methylomonas paludis (8.8 vs. 27.4%) were determined as the common genera in the diazotrophic and methanotrophic communities, respectively, with both proportions undergoing significant shifts under SN conditions. Whereas the LN condition led to high CH₄ oxidation activity and a relatively high abundance of Methylocystis (26.0%) in the roots of Kongyu131 rice, which sharply decreased under the SN condition (0.3%). The findings revealed that CH₄ oxidation-dependent N₂ fixation and CH₄ oxidation activities of root-associated type I methanotrophs were significantly affected under nitrogen fertilization, with a more pronounced effect in the salt-alkali tolerant J3 rice cultivar compared to Kongyu131. This study highlights the potential of aerobic diazotrophic methanotrophs in enhancing symbiotic diversity and environmental adaptability while contributing to CH₄ emission reduction and bioavailable nitrogen accumulation in saline-alkali paddy fields.