Sublethal doses of ZnO nanoparticles remodel production of cell signaling metabolites in the root colonizer Pseudomonas chlororaphis O6

Abstract

Cell signaling molecules function in regulating activities both within the producing bacterium as well as between cells. This paper shows that ZnO nanoparticles effectively disrupt cell signaling in a rhizosphere-competent bacterium, Pseudomonas chlororaphis O6. The reduced production of phenazines observed with increasing doses of ZnO NPs correlated with lowered levels of the quorum sensing molecules, acylhomoserine lactones (AHSLs). The ZnO NPs had a higher efficacy than Zn ions in these responses. Linked with changes to phenazine production was an effect on Fe metabolism manifested by enhanced siderophore production as Zn concentration from NPs or ions increased. The ZnO NPs induced phenotypes of lowered phenazines, AHSLs and increased siderophores are those observed with a mutant lacking the global regulator GacS. These metabolic changes caused by exposure to ZnO NPs could alter the way in which the bacterium functions in the rhizosphere.