Insights into the microbial response mechanisms to ciprofloxacin during sulfur-mediated biological wastewater treatment using a metagenomics approach

•Metagenomics analysis was applied to investigate the impacts of ciprofloxacin on sulfate-reducing bioprocess.•Ciprofloxacin induced microbial SOS responses such as activating efflux pump and DNA repair systems.•Functional genes involved in C, S and amino acid metabolisms were up-regulated.•Ciprofloxacin promoted the cooperation between microbes.•Species with a high complementarity index played pivotal roles against ciprofloxacin exposure.