Effects of graphene oxide on the diatom Nitzschia palea are associated with carbon cycling disturbance

Graphene based nanomaterials (GBMs) have been drawing the attention of the scientific communities these past years. As their market is increasing every year, their potential environmental and health risk are to be assessed. As microbial communities represent the basis of every ecosystem, it is essential to evaluate the risks of GBMs on these communities. The effects of GBMs on bacteria has been widely studied, while the effects on phototrophic species are less represented. In this study, the diatom Nitzschia palea was exposed to graphene oxide (GO) and reduced graphene oxide (rGO), at 0.1, 1 and 10 mg L−1. rGO had no effect on the diatom while GO induced an increase in growth, indicating the importance of the oxidation rate in the observed effect. Further results showed that shading effect of GO was countered by increased chlorophyll contents and by the accumulation of GO into the biofilm. This “sticking” mechanism increased the proximity between the biofilm and the GO, which might favour interactions between GO and the biofilm. These interactions led to the increase of defects and the reduction of GO. In addition, increased heterotrophic activity was suggested. To our knowledge, no diatom before Nitzschia palea has been shown to enhance its growth in presence of a GBM, but also capable to modify it. These results demonstrate the potential of GBMs, and in particular those with higher oxidation rates, to disrupt the contribution of the diatom Nitzschia palea to carbon cycling, which could have broader consequences at ecosystem scale. [Display omitted]