An integrated meta-omics approach reveals the different response mechanisms of two anammox bacteria towards fluoroquinolone antibiotics

Abstract

Abstract Background: The emerging fluoroquinolone antibiotics (FQs) are highly influential in nitrogen removal from livestock wastewater. However, beyond the capability of nitrogen removal, little is known about the molecular mechanism (e.g., shift of core metabolism and energy allocation) of anaerobic ammonium-oxidizing bacteria(AnAOB) under continuous FQ stress. Results: This study investigated the effectsof ciprofloxacin, ofloxacin and their mixture at concentrations detected in livestock wastewater on an anammox community in membrane bioreactors.It was found 20 μg/L FQs promoted nitrogen removal efficiency and community stability. Integrated meta-omics analysis revealed varied gene expression patterns between the two dominant AnAOB, Candidatus Brocadia sapporoensis (B AnAOB) and Candidatus Kuenenia stuttgartiensis (K AnAOB). The nitrogen metabolic processes were bolstered in B AnAOB, while those involved in anammox pathway of K AnAOB were inhibited. This difference was tentatively attributed to the up-regulation of reactive oxygen species scavenger genes (ccp and dxf) and FQ resistance gene (qnrB72) in B AnAOB. Importantly, most enhanced core biosynthesis/metabolism and close cross-feeding of B AnAOB with accompanying bacteria were also likely to contribute to higher levels of biomass yield and metabolism activity under FQ stress. Conclusions: This finding suggests that B AnAOB has the advantage of higher nitrogen metabolism capacity over K AnAOB in livestock wastewater containing FQs, which is helpful for efficient and stable nitrogen removal by anammox community.