Response of microbial communities based on full-scale classification and antibiotic resistance genes to azithromycin and copper combined pollution in activated sludge nitrification laboratory mesocosms at low temperature.

[Display omitted] • Nitrification was inhibited in stress- and post-effects of combined pollution. • Response of abundant taxa was more obvious than rare taxa to combined pollution. • CRAT were keystone taxa in network based on the full-scale classification method. • AOA and aerobic denitrifying bacteria were enriched at high AZM concentration. • Nonpathogenic bacteria and functional genera were the main hosts of ARGs. This study aimed to investigate the short-term response of abundant-rare genera and antibiotic resistance genes (ARGs) to azithromycin (AZM, 0.05–40 mg/L) and copper (1 mg/L) combined pollution in activated sludge nitrification system at low temperature. Nitrification was as expected inhibited in stress- and post-effects periods under AZM concentration higher than 5 mg/L. Abundant and rare taxa presented dissimilar responses based on full-scale classification. Conditionally rare or abundant taxa (CRAT) were keystone taxa. Relative abundance of ammonia-oxidizing archaea increased, and three aerobic denitrifying bacteria (Brevundimonas , Comamonas and Trichococcus) were enriched (from 9.83% to 68.91% in total). Ammonia nitrogen assimilating into Org-N and denitrification may be nitrogen pathways based on predict analysis. 29 ARGs were found with more co-occurrence patterns and high concentration of AZM (greater than 5 mg/L) caused their proliferation. Importantly, expect for some abundant taxa, rare taxa, potential pathogens and nitrogen-removal functional genera were the main potential hosts of ARGs. [ABSTRACT FROM AUTHOR]