[Short-term Effect of Roxithromycin on Abundance and Diversity of Ammonia-Oxidizing Microorganisms in Activated Sludge]

In this study, the short-term effect of roxithromycin(ROX) on the abundance and diversity of ammonia-oxidizing archaea(AOA) and ammonia-oxidizing bacteria(AOB) based on amoA gene in activated sludge were investigated by high-throughput sequencing and quantitative real-time PCR(qPCR). High-throughput sequencing overcomes the drawbacks of low sequencing depth, significant randomness and great bias of traditional Sanger sequencing. This approach can provide enough sequencing depth to comprehensively investigate the sensitive and insensitive ammonia-oxidizing microorganisms under ROX selective pressure. Lab-scale reactors were operated under ten different ROX levels. The results indicated that the environmental(0.3-30 μg·L^-1) and medium(300 μg·L^-1and 3000 μg·L^-1) levels of ROX did not affect ammonia oxidation, while the higher concentration(5000-12000 μg·L^-1) of ROX showed a significant negative effect on ammonia oxidation. The environmental and medium levels of ROX stimulated the growth of AOA, however, the higher level of ROX decreased the abundance of AOA. In addition, different levels of ROX(except 0.3 μg·L^-1) caused the decrease of the abundance of AOB, which suggested that AOA was less sensitive than AOB under ROX selective pressure. The results of high-throughput sequencing showed that ROX selective pressure caused the decrease of the numbers of OTUs for AOA and increase of that for AOB. The insensitive AOA, accounting for 57.70%-97.81% of the total sequences, were Candidatus Nitrososphaera gargensis and Candidatus Nitrosoarchaeum koreensis. The insensitive AOB were Nitrosomonas oligotropha, Nitrosospira multiformis, Nitrosomonas watsonii and Nitrosomonas halophilus, accounting for 0.76%-5.10% of the total sequences. These results also indicated that AOA was insensitive to ROX, but AOB was sensitive to ROX. RDA analyses showed that AOA Ca. Nitrososphaera gargensis, Ca. Nitrosoarchaeum koreensis and AOB N. oligotropha, N. watsonii, N. halophilus were positively correlated with ROX concentrations.