Unravelling mechanisms of bacterial quorum sensing disruption by metal-based nanoparticles

Nanoparticles are released in the environment causing a negative impact in several ecosystems such as microbial communities. To adapt to environmental changes some bacteria use a collective behaviour ruled by a cell-to-cell communication process called quorum sensing (QS). In this study, the impact of some of the most employed metal-based nanoparticles, such as zinc oxide nanoparticles (ZnONPs), titanium dioxide nanoparticles (TiO₂NPs) and silver nanoparticles (AgNPs) on bacterial QS has been assessed by using two different strains of the model organism Chromobacterium violaceum and by employing different experimental conditions. TiO₂NPs were tested with and without applying a previous step of UV-irradiation while the effect of AgNPs of two diameter sizes (40 and 60 nm) and two different coating agents (PVP and citrate) was evaluated. Results evidenced that all nanoparticles produced a significant effect on violacein production and therefore, in the QS system. ZnONPs mainly disrupted the QS steps related to signal perception and response whereas TiO₂NPs and AgNPs affected the autoinducer biosynthesis. AgNPs with the smallest size and citrate as capping agent produced the most deleterious effect while the impact of TiO₂NPs was not affected by UV irradiation. The present study provides new insights into the mechanisms by which these commonly employed metal-based nanoparticles disturb bacterial QS-based communication and clearly evidences the potential risk of releasing nanoparticles to the environment, especially for microbial communities which play a key role in many environmental and technological processes.