## 3 Results and Discussion
### Effect of Antibiotics on Ecological Effects of BRC-MFC  
Changes in Microbial Community Characteristics under Combined TC and OFLX Stresses The microbial diversity indices in different BRC-MFC reactors of stage I and stage II are shown in Table 2. Under antibiotic stress, both richness and chao1 values decreased, indicating that the microbial richness and total number of species decreased. The decrease in stage II was greater than that in stage I, indicating that the inhibitory effect of combined antibiotic stress on microorganisms was stronger than that of single antibiotic stress. The Shannon and Simpson indices did not show significant regular changes, indicating that the homogeneity and diversity of microbial communities did not feel the effect of antibiotic stress. Due to different classes of antibiotic stress at different concentrations, the distribution of microbial communities in different BRC-MFC reactors also differed. As shown in Figure 4a, the top 12 bacteria in terms of phylum level were _Proteobacteria_, _Bacteroidetes_, _Acidobacteria_, _Actinobacteria_, _Planctomycetes_, _Chlorofelxi_, _Verrucomicobia_, _Patescibacteria_, _Gematinomatedes_, _Nitrospirae_, _Frimicates_ and _Cyanobacteria_. It has been shown that _Proteobacteria_ (39.49% to 58.50%), _Bacteroidetes_ (15.33% to 29.67%) and _Chlorofelxi_ (0.22% to 3.03%) are the dominant phylum in wetland systems [65,66]. Furthermore, the phylum contains a variety of bacteria that efficiently degrade organic pollutants [67]. In addition, _proteobacteria_ and _Chlorofelxi_ are important microorganisms for nitrogen and phosphorus removal [68]. Firmicutes is a nitriifying bacterium that oxidizes nitrite to nitrate, ranked 11 th in terms of abundance (0.14-1.43%). Compared to R0, there was a significant increase in the abundance of planctomycetes and a decrease in the abundance of patecobacteria under antibiotic stress. Similar studies by other investigators have shown that when BRC was under two-antibiotics stress, the top 10 bacteria in terms of phylum level are _Proteobacteria_, _Bacteroidetes_, _Chlorofelxi_, _Patescibacteria_, _Aicidobacteria_, _Actinobacteria_, _Frimicates_, _Spirochaetes_, _Verrucomicrobia_ and _Gematinomatedes_[13]. Among them, nine kinds of bacteria in terms of phylum level were consistent in our study. As shown in Figure 4b, the top 12 bacteria in terms of genus level were Rhodanobacter, Holophaga, Zoogleoa, Aeromonas, Pseudomonas, Nakamuraella, Ferrobacterium, Flaviumbacter, Nitrosospira, Schlesneria, Dechloromonas and Tsukamurella. The abundance of the dominant genera in the different BRC-MFC reactors varied widely. In the absence of antibiotic stress, the dominant genera were Rhodanobacter (7.20%), Tsukamurella (1.76%), Dechloromonas (1.58%) and Pseudomonas (1.07%). After antibiotic stress, the dominant homogeneous genera changed to Rhodanobacter (7.25-28.87%), Holophaga (1.35-11.30%) and Aeromonas (0.08-15.08%). Only the specific dominant species of Rhodanobacter in BRC-MFC did not change, but its abundance increased to 28.87% after coming under antibiotic stress. Nitrosospira belongs to the nitriifying bacteria that oxidize NH\({}_{4}\)+-N to NO\({}_{2}\)[69]. OFLX stress at 2.4 ug\(\cdot\)mL\({}^{-1}\) and 3.6 ug\(\cdot\)mL\({}^{-1}\) increased the abundance of Nitrosospira to 2.47% and 2.09%, respectively, which could enhance the nitrification efficiency. Similar studies by other investigators have shown that when BRC was under two-antibiotics stress, the top 10 bacteria in terms of genus level are Blrii41, denitratisoma, Ferrobacterium, Thiobacillus, Saccharomyadales, Bacteroidetes_vadinHA17, Desulfomicrobium, Sbr1031, Treponema_2 and Subgroup_7 [13]. There were only one kind of bacteria in terms of genus level was consistent in this study.