Table_1_From waste to protein: a new strategy of converting composted distilled grain wastes into animal feed.DOCX

Distilled grain waste (DGW) is rich in nutrients and can be a potential resource as animal feed. However, DGW contains as much as 14% lignin, dramatically reducing the feeding value. White-rot fungi such as Pleurotus ostreatus could preferentially degrade lignin with high efficiency. However, lignin derivatives generated during alcohol distillation inhibit P. ostreatus growth. Thus, finding a new strategy to adjust the DGW properties to facilitate P. ostreatus growth is critical for animal feed preparation and DGW recycling. In this study, three dominant indigenous bacteria, including Sphingobacterium thermophilum X1, Pseudoxanthomonas byssovorax X3, and Bacillus velezensis 15F were chosen to generate single and compound microbial inoculums for DGW composting to prepare substrates for P. ostreatus growth. Compared with non-inoculated control or single microbial inoculation, all composite inoculations, especially the three-microbial compound, led to faster organic metabolism, shorter composting process, and improved physicochemical properties of DGW. P. ostreatus growth assays showed the fastest mycelial colonization (20.43 μg·g−1 ergosterol) and extension (9 mm/d), the highest ligninolytic enzyme activities (Lac, 152.68 U·g−1; Lip, 15.56 U·g−1; MnP, 0.34 U·g−1; Xylanase, 10.98 U·g−1; FPase, 0.71 U·g−1), and the highest lignin degradation ratio (30.77%) in the DGW sample after 12 h of composting with the three-microbial compound inoculation when compared to other groups. This sample was relatively abundant in bacteria playing critical roles in amino acid, carbohydrate, energy metabolism, and xenobiotic biodegradation, as suggested by metagenomic analysis. The feed value analysis revealed that P. ostreatus mycelia full colonization in composted DGW led to high fiber content retention and decreased lignin content (final ratio of 5% lignin) but elevated protein concentrations (about 130 g·kg−1 DM). An additional daily weight gain of 0.4 kg/d was shown in cattle feeding experiments by replacing 60% of regular feed with it. These findings demonstrate that compound inoculant consisting of three indigenous microorganisms is efficient to compost DGW and facilitate P. ostreatus growth. P. ostreatus decreased the lignin content of composted DGW during its mycelial growth, improving the quality of DGW for feeding cattle.

蒸馏谷物废弃物（distilled grain waste, DGW）富含营养物质，可作为动物饲料的潜在资源。然而，DGW中木质素含量高达14%，大幅降低了其饲用价值。糙皮侧耳（Pleurotus ostreatus）等白腐真菌可高效优先降解木质素，但酒精蒸馏过程中产生的木质素衍生物会抑制糙皮侧耳的生长。因此，寻找新的策略以调控DGW的特性、促进糙皮侧耳生长，对于动物饲料制备及DGW的资源化循环利用至关重要。
本研究选取了3株优势土著细菌，分别为嗜热鞘氨醇杆菌X1（Sphingobacterium thermophilum X1）、食棉假黄单胞菌X3（Pseudoxanthomonas byssovorax X3）以及贝莱斯芽孢杆菌15F（Bacillus velezensis 15F），用于制备单一及复合微生物菌剂，以对DGW进行堆肥处理，从而获得可供糙皮侧耳生长的基质。与未接种的对照组或单一微生物接种组相比，所有复合接种组均表现出更快的有机物代谢速率、更短的堆肥周期，且改善了DGW的理化性质。
糙皮侧耳生长试验表明，与其他组相比，经3株微生物复合菌剂堆肥12小时后的DGW样品，其菌丝定殖速度最快（麦角固醇含量达20.43 μg·g⁻¹）、菌丝扩展速率最高（9 mm/d），木质素降解酶活性最优：漆酶（Lac）为152.68 U·g⁻¹、木质素过氧化物酶（Lip）为15.56 U·g⁻¹、锰过氧化物酶（MnP）为0.34 U·g⁻¹、木聚糖酶为10.98 U·g⁻¹、滤纸酶（FPase）为0.71 U·g⁻¹，且木质素降解率最高（30.77%）。宏基因组分析显示，该样品中参与氨基酸代谢、碳水化合物代谢、能量代谢以及异生物质生物降解的细菌类群相对丰富。
饲用价值分析结果显示，经堆肥处理后的DGW中糙皮侧耳菌丝完全定殖后，可保留较高的纤维含量，同时降低木质素含量（最终木质素占比为5%），并提升蛋白质浓度（干物质基础约为130 g·kg⁻¹）。肉牛饲喂试验表明，用该堆肥替代60%的常规饲料时，肉牛可实现额外0.4 kg/天的增重。
上述研究结果表明，由3株土著微生物组成的复合菌剂可高效实现DGW堆肥，并促进糙皮侧耳的生长。糙皮侧耳在菌丝生长过程中可降低堆肥后DGW的木质素含量，从而提升其作为肉牛饲料的品质。