Metagenomics analysis unraveled the dynamics of microbial community and antibiotic resistance genes during the composting of spiramycin fermentation residue following acidic hydrothermal treatment

The sustainable management of spiramycin fermentation residue (SFR), classified as hazardous waste, is a significant challenge. Due to its high organic matter content, composting for transforming SFR into organic fertilizer is a promising disposal approach. Acidic hydrothermal treatment (AHT) has been demonstrated to effectively eliminate residual spiramycin (SPM) from SFR, enhancing its biodegradability. This study conducted a comprehensive investigation into the effects of AHT on the maturation process, microbial community structure, antibiotic resistance genes (ARGs), and metabolic mechanisms during SFR composting. AHT elevated the composting temperature and promoted the degradation of organic matter, increasing maturity (as indicated by the NH₄⁺-N/NO₃⁻-N ratio) by 12.2 %–24.5 %. AHT significantly influenced community composition during composting and facilitated the enhancement of species diversity. Additionally, it significantly reduced the abundance of ARGs (38.0 %–54.0 %) and mobile genetic elements (MGEs) (16.0 %–28.0 %), exhibiting a pronounced inhibitory effect on high-risk ARGs. The predominant hosts of ARGs and MGEs were Bacillota (47.5 %) and Proteobacteria (16.1 %). Additionally, AHT significantly diminished the relative abundance of virulence factor genes (VFGs) (6.6 %–11.6 %) while enhancing microbial metabolism, particularly within carbohydrate and amino acid pathways. These findings indicate that combining AHT with composting represents an effective pathway for resource utilization of SFR.