Graphene oxide affects soil bacterial and fungal diversity even at parts-per-trillion concentrations

Abstract

Graphene oxide (GO) is an oxidized form of graphene that is relatively cheap and easy to produce. This has heralded its widespread use in a range of industries, with its likelihood of release into the environment increasing accordingly. In pure culture, GO has been shown to influence bacteria and fungi, but its effects on environmental microbial communities remain poorly characterized, despite the important ecosystem services that these organisms underpin. Here, we characterized the effects of GO and graphite, over time and at three concentrations (1 ng, 1 {micro}g and 1 mg kg dry soil-1), on soil bacterial and fungal diversity using 16S rRNA and ITS2 gene amplicon sequencing. Graphite was included as a reference material as it is widely distributed in the environment. Neither GO or graphite had significant effects on the alpha diversity of microbial communities. The composition of bacterial and fungal communities, however, was significantly influenced by GO and graphite. These effects were equally apparent between doses and varied over time. Predicted KEGG pathways and fungal guild structures were not significantly influenced by the treatments. Our study demonstrates that GO can influence soil microbial diversity, even at parts-per-trillion concentration, which is equivalent to the rates of release predicted for similar nanomaterials such as carbon nanotubes. ImportanceGraphene oxide is a nanomaterial with broad and expanding industrial applications. Some evidence indicates that it can influence the growth of microorganisms, many of which support important ecosystem services, such as the provision of food and clean water. The amount of graphene oxide currently entering soils is not known but is likely to be similar to other nanomaterials, such as carbon nanotubes (i.e. parts-per-trillion to parts-per-billion per year). In this study, we demonstrate that graphene oxide added to soil at these concentrations (or higher) can alter the composition of bacterial and fungal communities. Nonetheless, we found that these changes were of similar magnitude to those associated with the addition of graphite, which is common and occurs naturally in soils. Further research is recommended to determine whether the changes in microbial community composition that we have shown can be induced by graphene oxide, have deleterious consequences for soil health.