Abstract: This study investigated the effects of tetracycline mass concentration and tetracycline degrading bacteriumSerratia entomophilastrain TC-1 on the removal rate of pollutants in the microalgal-bacterial symbiotic system. Through scanning electron microscopy observation and high-throughput sequencing technology, the changes in microbial community structure were further analyzed to reveal the pollutant removal patterns and microbial response mechanisms of the bacterial algal symbiotic system under tetracycline stress. The research results showed that the higher the tetracycline concentration, the lower the microalgal biomass, and the lower the ammonia nitrogen removal rate of the microalgal-bacterial symbiotic system. When the mass concentration of tetracycline was 50 mg/L, the chlorophyll mass concentration was 19.19 mg/L, and the ammonia nitrogen removal rate of the microalgal-bacterial symbiotic system was the lowest, at 75.27%. Through scanning electron microscopy observation, it was found that bacteria could alleviate the stress effect of tetracycline by attaching to the surface of microalgae cells and secreting extracellular polymeric substances. Microbial community analysis showed that the mass concentration of tetracycline had a significantly greater impact on bacterial community structure than the inoculation of degrading bacteria. Inoculating degrading bacteria alleviated the effects of low mass concentrations of tetracycline on bacterial community structure. The tetracycline degrading bacteriaTrichococcusreduced the impact of low mass concentrations of tetracycline on the microalgal bacterial consortia, while the stress resistant bacteriaPseudomonasand denitrifying polyphosphate accumulating bacteriaComamonasreduced the impact of high mass concentrations of tetracycline on the microalgal bacterial consortia.

Key words: microalgal bacterial consortia, tetracycline, degrading bacteria, nurtients removal, microbial community