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Microorganisms, such as bacteria, are one of the first targets ofnanoparticles in the environment. In this study, we tested the effect of twonanoparticles, ZnO and TiO2, with the salt ZnSO4 as the control, on theGram-positive bacterium Bacillus subtilis by 2D gel electrophoresis-basedproteomics. Despite a significant effect on viability (LD50), TiO2 NPs had nodetectable effect on the proteomic pattern, while ZnO NPs and ZnSO4significantly modified B. subtilis metabolism. These results allowed us toconclude that the effects of ZnO observed in this work were mainly attributableto Zn dissolution in the culture media. Proteomic analysis highlighted twelvemodulated proteins related to central metabolism: MetE and MccB (cysteinemetabolism), OdhA, AspB, IolD, AnsB, PdhB and YtsJ (Krebs cycle) and XylA,YqjI, Drm and Tal (pentose phosphate pathway). Biochemical assays, such as freesulfhydryl, CoA-SH and malate dehydrogenase assays corroborated the observedcentral metabolism reorientation and showed that Zn stress induced oxidativestress, probably as a consequence of thiol chelation stress by Zn ions. Theother patterns affected by ZnO and ZnSO4 were the stringent response and thegeneral stress response. Nine proteins involved in or controlled by thestringent response showed a modified expression profile in the presence of ZnONPs or ZnSO4: YwaC, SigH, YtxH, YtzB, TufA, RplJ, RpsB, PdhB and Mbl. Anincrease in the ppGpp concentration confirmed the involvement of the stringentresponse during a Zn stress. All these metabolic reorientations in response toZn stress were probably the result of complex regulatory mechanisms includingat least the stringent response via YwaC.

Zinc oxide induces the stringent response and major reorientations in the central metabolism of Bacillus subtilis