Oxytetracycline stress stimulates antibiotic resistance gene proliferation and quorum sensing response of marine anammox bacteria in seawater-based wastewater treatment

Seawater-based wastewater is characterized by high concentrations of oxytetracycline (OTC) and salt, which is a huge challenge for conventional biological nitrogen removal processes. Marine anammox bacteria (MAB) are recently employed for nitrogen removal from saline wastewater due to their good salt tolerance. This study focuses on the impacts of OTC on MAB for nitrogen removal from seawater-based wastewater for the first time, particularly highlighting the antibiotic resistance gene (ARG) proliferation and quorum sensing (QS) response. At low OTC doses (<= 7 mg L-1), MAB had a good tolerance and the total nitrogen removal efficiency was maintained at 77%. When OTC dose reached 22 mg L-1, the activity of MAB was inhibited obviously. The relative abundance of MAB drastically decreased to 4.1% from 14.41% when OTC dose increased to 22 from 0 mg L-1. On contrary, antibiotic resistance bacteria gradually became the dominant population in reactor with increasing OTC content, accompanying along with the increase of relative abundance of ARGs. The tolerance of MAB-based consortia to OTC toxicity was enhanced by the high expression of ARGs. Besides, more extracellular polymeric substance was secreted to enhance anammox granule tolerance against OTC toxicity, which was promoted by the high release of signal molecule (3OC6-HSL). Furthermore, the expression of hdh and tetM was regulated by QS to enhance MAB -based consortia tolerance under OTC stress. Therefore, the tolerance of anammox consortia to OTC was mainly attributed to proliferated ARGs and active QS. This work exploited the significant potential of MAB in seawater-based wastewater treatment.