# Biodegradation of Sulfamethoxazole in Milkfish (_Chanos chanos_) Pond Sediments
## 3 Results and Discussion
### Test of Sulfamethoxazole-Degrading Ability of Isolated Bacteria
These results indicated that the microbial communities shifted after 40 days of SMX readdition, which may be due to SMX adaptation. Figure 8: Biodegradation of sulfamethoxazole (SMX) by bacterial strains A12 and L (with fish pond sediments) in aerobic and anaerobic readdition experiments, respectively. (**A**) Aerobic SMX biodegradation with/without strain A12. (**B**) Major representatives of the microbial community in aerobic experiments with strain A12. (**C**) Major representatives of the microbial community in aerobic experiments without strain A12. (**D**) Anaerobic SMX biodegradation with/without strain L. (**E**) Major representatives of the microbial community in anaerobic experiments with strain L. (**F**) Major representatives of the microbial community in anaerobic experiments without strain L. Red stars indicate that SMX-degrading bacteria have been reported. Red “@”s indicate SMX-degrading bacteria isolated in this study. Proportions of microbes with a statistically significant difference between experiments with and without bacterial strains A12 and L were identified using the Mann–Whitney U-test (\(p<0.05\)). Seventeen bacterial genera, including one reported SMX-degrading bacterial genus (_Escherichia/Shigella_) [16], exhibited a higher proportion in the experiment with strain A12 (Figure 8B). Fourteen bacterial genera, including one reported SMX-degrading bacterial genus (_Nitrosomonas_) [14], exhibited a higher proportion in experiments without strain A12 (Figure 8C). Eighteen bacterial genera, including two reported SMX-degrading bacterial genera (_Pseudomonas_ and _Desulfoibrio_) [15; 19], exhibited a higher proportion in experiments with strain L (Figure 8E). Fourteen bacterial genera, including one reported SMX-degrading bacterial genus (_Escherichia/Shigella_) [16], exhibited a higher proportion in experiments without strain L (Figure 8F). These results indicated that different microbial communities occurred after 40 days of SMX readdition under aerobic and anaerobic conditions. Moreover, different microbial community compositions exhibited different SMX-degrading abilities (Figure 8A,D). Mariculture and coastal aquaculture activities can lead to pollution by micropollutants (e.g., antibiotics) in coastal seawater, which host the highest biodiversity in the world. Thus, it is important to investigate bioremediation solutions for organic micropollutants in coastal waters [20]. The study of [PERSON] and [PERSON] (2009) indicated that the microbial degradation of pharmaceuticals, such as sulfamethoxazole and trimethoprim, in and near a wastewater-polluted estuarine and coastal seawater and sediments, is much slower than the degradation of biomolecules, such as glucose and amino acids [13]. It has been reported that chronic exposure to low concentrations and legal aquaculture doses of SMX causes systemic adverse effects and provoke differential human health risks in Nile tilapia [21]. For aquaculture, SMX is commonly administered at 100 to 200 mg kg\({}^{-1}\) fish body weight/day for five days [22], depending on fish species, infection, and country-specific legal requirements. The SMX concentrations used in this study were extremely higher than what would be expected in the environment. However, they are reasonable for aquaculture wastewater treatment.