Identification of Soil Bacteria Susceptible to TiO 2 and ZnO Nanoparticles

Because soil is expected to be a major sink for engineered nanoparticles (ENPs) released to the environment, the effects of ENPs on soil processes and the organisms that carry them out should be understood. DNA-based fingerprinting analyses have shown that ENPs alter soil bacterial communities, but specific taxon changes remain unknown. We used bar-coded pyrosequencing to explore the responses of diverse bacterial taxa to two widely used ENPs, nano-TiO2 and nano-ZnO, at various doses (0, 0.5, 1.0, and 2.0 mg g−1 soil for TiO2 ; 0.05, 0.1, and 0.5 mg g−1 soil for ZnO) in incubated soil microcosms. These ENPs significantly altered the bacterial communities in a dose-dependent manner, with some taxa increasing as a proportion of the community, but more taxa decreasing, indicating that effects mostly reduced diversity. Some of the declining taxa are known to be associated with nitrogen fixation (Rhizobiales ,Bradyrhizobiaceae , andBradyrhizobium ) and methane oxidation (Methylobacteriaceae ), while some positively impacted taxa are known to be associated with the decomposition of recalcitrant organic pollutants (Sphingomonadaceae ) and biopolymers including protein (Streptomycetaceae andStreptomyces ), indicating potential consequences to ecosystem-scale processes. The latter was suggested by a positive correlation between protease activity and the relative abundance ofStreptomycetaceae (R = 0.49,P = 0.000) andStreptomyces (R = 0.47,P = 0.000). Our results demonstrate that some metal oxide nanoparticles could affect soil bacterial communities and associated processes through effects on susceptible, narrow-function bacterial taxa.