Top-down selection of pit mud local microbial community for efficient anaerobic digestion of distilled grain waste

China's annual production of 12 million tons of distilled grain waste (DGW) from Baijiu manufacturing poses significant environmental challenges. Conventional anaerobic digestion (AD) using wastewater sludge exhibits poor compatibility with DGW's unique physicochemical properties, achieving suboptimal methane yields. This study pioneered a top-down domestication strategy employing indigenous pit mud (PM) microbiome as a specialized inoculum for enhanced DGW valorization. PM-based reactors demonstrated superior performance over anaerobic sludge (AS), achieving 73 % higher biogas yields (518.52 vs 298.99 mL/g VTS) and 95 % higher methane productivity (246.65 vs 126.81 mL/g VTS). Peak methane yields reached 432.59 mL/g VTS, establishing a new benchmark for DGW digestion. Comprehensive 16S rRNA sequencing revealed dynamic microbial succession during 91-day domestication, with Firmicutes becoming dominant (>90 %) under thermophilic conditions. Community assembly mechanisms shifted from deterministic homogeneous selection (76-88 %) to stochastic ecological drift (76 %), reflecting adaptive microbial restructuring. PICRUSt2 functional analysis unveiled strategic metabolic reprogramming: PM consortia upregulated glycolysis and ATP synthesis pathways while downregulating citrate cycles, optimizing carbon flux toward substrate-level energy generation. The domesticated PM microbiome exhibited remarkable resilience, rapidly recovering from operational perturbations while maintaining stable volatile fatty acid profiles. This work establishes the first successful application of substrate-adapted indigenous microbiota as specialized AD inoculum for DGW, offering a sustainable circular bioeconomy solution for China's massive DGW waste stream while advancing fundamental understanding of microbial community domestication mechanisms.