Mechanistic evaluation of enhanced graphene toxicity to Bacillus induced by humic acid adsorption

Abstract

The extensive application of graphene nanosheets (GNSs) has raised concerns over risks to sensitive species in the aquatic environment. The humic acid (HA) corona is traditionally considered to reduce GNSs toxicity. Here, we evaluated the effect of sorbed HA (GNSs-HA) on the toxicity of GNSs to Gram positive Bacillus tropicus. Contrary to previous data, GNSs-HA exhibited greater toxicity than bare GNSs. Multi-omics combined with sensitive bioassays and electrochemical methods demonstrated that bare GNSs disrupted oxidative phosphorylation by causing physical membrane damage. This led to the accumulation of intracellular reactive oxygen species and inhibition of ATP production, subsequently suppressing metabolic processes and ultimately causing bacterial death. Conversely, GNSs-HA directly extracted electrons from bacteria and oxidized biomolecules due to HA-improved electron transfer. This finding suggests that the HA corona does not always mitigate the toxicity of engineered nanoscale pollutants (ENPs), thereby introducing uncertainty over the interaction between the environmental corona and ENPs during ecological risk evaluation.