Response of soil microbial communities to engineered nanomaterials in presence of maize (Zea mays L.) plants

With the intended application of engineered nanomaterials (ENMs) in agriculture, accurate assessment the effect of these ENMs on soil microbial communities is especially necessary. Here, maize plants were cultivated in soil amended by SiO₂, TiO₂, and Fe₃O₄ ENMs (100 mg kg^-1 soil) for four weeks. The impact of ENMs on bacterial community structure of the rhizosphere soil was investigated by using high-throughput sequencing. In addition, metabolites of maize rhizosphere soil were quantified by gas chromatography-mass spectrometry (GC-MS) based metabolomics. We found that the disturbance of ENMs on soil microbes are in the follow of Fe₃O₄>TiO₂>SiO₂. Exposure of Fe₃O₄ ENMs significantly reduced the abundance of nitrogen-fixation related bacteria Bradyrhizobiaceae (from 2.94% to 2.40%) and iron-redox bacteria Sediminibacterium (from 2.15% to 2.07%). Additionally, Fe₃O₄ ENMs significantly increased populations of Nocardioides (from 1.63% to 1.77%), Chitinophaga sancti (from 1.12% to 2.08%), Pantoea (from 1.31% to 2.22%), Rhizobiumand (from 1.41% to 1.74%) and Burkholderia-Paraburkholderia (from 1.50% to 2.09%), which are associated with carbon cycling and plant growth promoting. This study provides a perspective on the response of rhizosphere microbial community and low molecular weight metabolites to ENMs exposure, providing a comprehensive understanding of the environmental risk of ENMs.

Evaluation of performance and microbial community successional patterns in an integrated OCO reactor under ZnO nanoparticle stress

An integrated OCO reactor was used to investigate the performance and microbial community successional changes under long-term exposure to relatively low levels of ZnO nanoparticles (NPs). Relatively higher concentrations of ZnO NPs (1.5 mg L⁻¹) could adversely affect the nitrogen and phosphorus removal in the reactor. The diversity and richness of the microbial communities chronically declined with an increasing concentration of ZnO NPs higher than 1.5 mg L⁻¹. With the elevated ZnO NPs, the phyla abundances of Proteobacteria, Firmicutes and Actinobacteria decreased slightly, whereas those of Bacteroidetes and Acidobacteria increased. Bacteroidetes and Proteobacteria were the predominant phyla in each phase (with a variation in abundance), together with some common taxa responses to ZnO NP stress as revealed by Venn diagram analysis. Some genera associated with the removal of nitrogen and phosphorus, such as Acinetobacter, Stenotrophomonas and Pseudomonas, decreased significantly. The present results are significant for expanding our understanding of the functional performance and microbial community successions of activated sludge which has experienced long-term exposure to environmentally relevant concentrations of ZnO NPs.

An integrated OCO reactor was used to investigate the performance and microbial community successional changes under a long-term exposure to relatively low-level ZnO nanoparticles (NPs).