Fate and Mechanism of Sulfamethoxazole Degradation by Hypoxic Microorganisms During Straw Return to Paddy Fields

To improve the degradation rate of sulfamethoxazole (SMX) under hypoxic conditions in paddy fields during the flooding period, a laboratory microcosm experiment was established in this study to investigate the regulatory effect of straw return on the hypoxic degradation of SMX and its underlying microbial mechanisms. The results demonstrated that straw addition significantly promoted the hypoxic degradation of SMX. By the 10th day of the experiment, the residual SMX content in the straw-amended group was only 11.3% of that in the non-straw control group, and the average degradation rate throughout the experimental period was increased by 85.7%. Straw provided complex carbon sources, including organic carbon (e.g., starch, sugars, and humus) and cellulose, which not only reshaped the microbial community structure and created new ecological niches but also increased the microbial network density under SMX stress from 0.010 to 0.024. Acinetobacter, Bacillus, and Pseudomonas, which possess both straw decomposition and SMX degradation capabilities, sequentially became the dominant bacterial taxa. These dominant taxa can adapt to hypoxic fermentation in the flooded environment and co-metabolize SMX by activating the metabolic pathways of aromatic compounds and sugars. This study is expected to open up a novel approach for the remediation of SMX-contaminated flooded paddy fields and provide valuable innovative insights for technological breakthroughs and practical applications in related fields.