Microbial denitrification has been regarded as an important process involved in global climate, water purification, and soil fertility, where nitrate can be consecutively reduced to nitrite, nitric oxide, nitrous oxide, and dinitrogen gas. Traditional anaerobic denitrification process, taking place in the absence of O2, has been proved to be negatively affected by the appearance of man-made nanoparticles (NPs). Recently, aerobic denitrification, has been received more and more attention, where nitrate can be aerobically reduced to nitrogenous gas. However, little is known about how man-made nanoparticles affects aerobic denitrification. Here, we investigated how nanoparticles (ZnO and TiO2 NPs) impact an aerobic denitrifier, Pseudomonas stutzeri PCN-1. The results showed the presence of ZnO and TiO2 NPs caused significant inhibition of aerobic denitrification, which led to delayed nitrate reduction, higher nitrite accumulation, and higher nitrous oxide emission. But the inhibition pattern under ZnO NPs exposure was distinctly different from that under TiO2 NPs exposure. When exposing to ZnO NPs, nitrate reduction was suppressed with the increase of ZnO NPs from 1 to 128 mg/L. Meanwhile, the inhibitions on gene expression and catalytic activities of nitrate reductase and nitrite reductase were also strengthened with the increment of ZnO NPs concentration. The generation of reactive oxygen species (ROS) were mainly responsible for the cytotoxicity of ZnO NPs. Under TiO2 NPs exposure, the inhibitory effect has been mitigated when TiO2 NPs concentrations increased from 1 to 128 mg/L. Meanwhile, the expressions of genes involving aerobic denitrification basically exhibited down-regulated patterns. The down-regulated folds at lower TiO2 NPs concentrations were much greater than that at higher concentrations. The formation of aggregates in the bacterial suspension was predominantly responsible for the cytotoxicity of TiO2 NPs. The decreased toxicities at higher concentrations could be attributed to the formation of larger aggregates, which greatly reduced the chance of direct interaction between the nanoparticles and cell walls. In our study, the mechanisms of bacteria-nanoparticle interaction were illuminated by investigating how NPs impact an aerobic denitrifier, Pseudomonas stutzeri PCN-1. These results were of significance to evaluating the potential ecological toxicity and risks of nanomaterials.

Effects of man-made nanoparticles on aerobic denitrification by strain Pseudomonas stutzeri PCN-1

2019 Fall National Meeting

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