New insights into the impact of nZVI on soil microbial biodiversity and functionality.

Nanoscale zero-valent iron (nZVI) is a strong reducing agent used for in situ remediation of soil. The impacts of nZVI (5-10% w/w) on the soil microbial biodiversity and functionality of two soils (Lufa 2.2 and 2.4) were assessed. Illumina MiSeq technology was used to evaluate the structure of soil microbiomes after 21 days of exposure. Proteobacteria, Verrucomicrobia, Firmicutes and Actinobacteria were the most abundant phyla in both soils. However, the dynamics of bacterial community composition following nZVI addition differed. nZVI exposure induced pronounced shifts in the microbial composition of soil 2.4, but not in soil 2.2; an increase in Verrucomicrobia abundance was the unique common taxonomic pattern observed in both soils. The PICRUSt approach was applied to predict the functional composition of each metagenome. Environmental information processing function (membrane transport) was decreased in both nZVI-spiked soils, although soil 2.4 samples were enriched in functions involved in cellular processes and metabolism. The effects of nZVI on autochthonous bacterial communities clearly varied with the soil type assessed; changes at the phylogenetic level appeared to be more abundant than those observed at the functional level, and thus, the overall effort of the soil ecosystem might involve the maintenance of functionality following nZVI exposure.