Microalgae Enhances\nthe Adaptability of Epiphytic\nBacteria to Sulfamethoxazole Stress and Proliferation of Antibiotic\nResistance Genes Mediated by Integron

The transmission of ARGs in the microalgae-associated\nepiphytic\nbacteria remains unclear under antibiotic exposure, apart from altering\nthe microbial community structure. In this study, Chlorella\nvulgaris cocultured with bacteria screened from surface\nwater was examined to explore the spread of ARGs in the presence of\nsulfamethoxazole (SMX). The extracellular polymers released by Chlorella vulgaris could reduce antibiotic-induced\ncollateral damage to bacteria, thus increasing the diversity of the\nmicroalgae-associated epiphytic bacteria. The abundances of <i>sul1</i> and <i>intI1</i> in the phycosphere at 1\nmg/L SMX dose increased by 290 and 28 times, respectively. Metagenomic\nsequencing further confirmed that SMX bioaccumulation stimulated the\nhorizontal transfer of <i>sul1</i> mediated by <i>intI1</i> in the microalgae-associated epiphytic bacteria, while reactive\noxygen species (ROS)-mediated oxidative stress induced the SOS response\nand thus enhanced the transformation of <i>sul1</i> in the\nJ group. This is the first study to verify that microalgae protect\nbacteria from antibiotic damage and hinder the spread of ARGs mediated\nby SOS response, while the transfer of ARGs mediated by integron is\npromoted due to the bioaccumulation of SMX in the phycosphere. The\nresults contribute to present comprehensive understanding of the risk\nof ARG proliferation by the presence of emerging contaminants residues\nin river.