Soy leghemoglobin, when bound to heme, imparts a meat-like color and flavor and can serve as a substitute for animal-derived proteins. Enhancing cellular heme synthesis improves the recombinant expression of leghemoglobin in yeast. To achieve high-level expression of leghemoglobin A (LBA) in Kluyveromyces marxianus, a food-safe yeast, large-scale heme synthesis modules were transferred into K. marxianus using yeast artificial chromosomes (KmYACs). These modules contained up to 8 native and heterologous genes to promote the supply of heme precursors and downstream synthesis. Next, eight genes inhibiting heme or LBA synthesis were individually or combinatorially deleted, with the lsc1Δssn3Δ mutant yielding the best results. Subsequently, heme synthesis modules were combined with the lsc1Δssn3Δ mutant. In the resulting strains, the module genes were all actively expressed. Among these module genes, heterologous S. cerevisiae genes in the downstream heme synthesis pathway significantly enhanced the expression of their counterparts in K. marxianus, resulting in high heme content and LBA yield. After optimizing the medium recipe by adjusting the concentrations of glucose, glycine, and FeSO₄·7H₂O, a heme content of 66.32 mg/L and an intracellular LBA titer of 7.27 g/L were achieved in the engineered strain in a 5 L fermentor. This represents the highest intracellular expression of leghemoglobin in microorganisms to date. The leghemoglobin produced by K. marxianus can be utilized as a safe ingredient for plant-based protein products.

Arsenic (As) and cadmium (Cd) are two prominent metal contaminants in mining soil, threatening food and environmental safety. The aim of this study was to explore an effective material to simultaneously reduce As and Cd uptake by plants growing in multi-contaminated soil. The effects of Fe-loaded biochar on the accumulation and translocation of As and Cd in a soil-lettuce system were investigated to evaluate the efficiency of Fe-loaded biochar in reducing As and Cd bioavailability. Application of Fe-loaded biochar at a rate of 0.5-1.5% decreased the concentrations of porewater As and Cd by 4.2-53.0% and -0.6-21.7%, respectively. The results of sequential extraction showed that Fe-loaded biochar can promote the transfer of As and Cd in soils from the available fraction to a relatively stable fraction, thus reducing the mobility and availability of As and Cd. The concentrations of As and Cd in lettuce shoots in the Fe-loaded biochar treatment were significantly decreased by 11.4-26.0% and 4.4-12.9% compared with those in the untreated soil, respectively. Fe-loaded biochar applied at a rate of 0.5-1.0% had no obvious effect on plant biomass, and the lowest weight of lettuce shoots and roots was observed in the treatment with Fe-loaded biochar applied at a rate of 1.5%, in which they were reduced by 12.9% and 18.0%, respectively. Overall, Fe-loaded biochar as a soil amendment was effective in simultaneously reducing As and Cd bioavailability in As and Cd co-contaminated soils, and an application rate lower than 1.5% is recommended to avoid significant decreases in plant growth.

(1) Background: We investigated the effects of nutrient levels on rice yield and nitrogen uptake, with the aim of improving rice yield and nitrogen use efficiency. (2) Methods: A 3-year field experiment was conducted using the rice variety Changliangyou Fuxiangzhan, with six treatments: no nitrogen application (CK), conventional fertilization (FP), single basal application of 60-day slow-release urea (CRU1), single basal application of urea combined with 40-day and 90-day slow-release urea (CRU2), partial substitution of chemical fertilizer with bio-organic manure (FPM), and conventional fertilization combined with straw return (FPS). (3) Results: Different nutrient management regimes significantly affected rice yield and nitrogen uptake and use, as well as soil nitrogen content. CRU2 achieved the highest performance across most indicators, with grain yield averaging 9.6% higher than that of FP and 36.4% higher than that of CK, alongside consistently greater effective panicle numbers. It also significantly enhanced nitrogen uptake, with higher grain and straw N accumulation, and showed the best nitrogen use efficiencies. Soil responses varied by treatment: FPS and FPM increased total nitrogen, while CRU2 and CRU1 had the highest inorganic nitrogen, and microbial biomass nitrogen peaked under FPM, CRU2, and FPS. Despite these benefits, CRU2 showed the largest negative nitrogen balance, averaging −33.0 kg ha⁻¹ over 3 years. (4) Conclusions: The CRU2 treatment achieved efficient synchronization between nitrogen supply and demand, with the highest yield, nitrogen uptake, and soil nitrogen levels.

Long-term reliance on mineral fertilizers may degrade soil structure and weaken carbon and nitrogen retention in rice–wheat rotation systems. Organic amendments combined with mineral fertilizers can provide organic substrates, promote aggregate formation, and improve soil C–N retention, but the contrasting effects of plant- and animal-derived amendments remain unclear. A long-term field experiment initiated in 2012 in Chaohu, China, compared no fertilization (CK), chemical fertilizer alone (CF), chemical fertilizer plus oil cake (OC), and chemical fertilizer plus cattle manure (CM). At wheat maturity in 2025, soil aggregate distribution, stability, aggregate-associated soil organic carbon (SOC) and total nitrogen (TN), C and N contribution rates, and yield components were determined; wheat yield was further evaluated using annual records from 2021 to 2025. Compared with CK, OC and CM increased water-stable macroaggregates (>0.25 mm) by 17.35% and 17.94% and reduced aggregate destruction by 54.61% and 53.57%, respectively. In large macroaggregates (>2 mm), OC and CM increased SOC by 58.30% and 84.83% and TN by 141.76% and 200.00%, respectively. Five-year mean yield increased by 208.09%, 240.78%, and 225.15% under CF, OC, and CM, respectively, relative to CK, but did not differ significantly among fertilized treatments. Overall, oil cake showed a numerical advantage in maintaining wheat yield, whereas cattle manure had greater potential to improve aggregate-scale C–N retention and soil structural stability.