Shifts of bacterial community and molecular ecological network in activated sludge system under ibuprofen stress

The major objectives of this study were to explore the long-term effects of ibuprofen (IBP) on nutrient removal, community compositions, and microbial interactions of the activated sludge system. The results showed that 1 mg/L IBP had no inhibitory effects on the removal of organic matters and nutrients. IBP significantly reduced the microbial diversity and changed the bacterial community structure. Some denitrifiers (Denitratisoma and Hyphomicrobium) increased significantly, while NOB (Nitrospira) significantly decreased under IBP stress (P < 0.05). Furthermore, molecular ecological network analysis indicated that IBP reduced the overall network size and links, but led to a closer network with more efficient communication, which might be the strategy of microbes to survive under the stress of IBP and further maintain the performance stability. Different phylogenetic populations had different responses to IBP, as a closer subnetwork with more synergistic relations was observed in Chloroflexi and a looser subnetwork with more competitive relationships was detected in Proteobacteria. The topological roles of nodes significantly changed, and the putative keystone species decreased under the stress of IBP. This study broadens our knowledge of the long-term effects of IBP on the microbial community structure and the interactions between species in the activated sludge system.