Electron-Transport-Chain-Mediated Selective Growth of Gold Nanocrystals in the Intermembrane Space of Live Microbial Cells

Hybridization of microbial cells with inorganic nanoparticles that could dramatically improve cellular functions such as electron transfer has been realized by the random attachment or stochastic entry of the nanoparticles. Clearly, the selective growth of inorganic nanoparticles on target functional organelles is ideal for such hybridization. Here, we report the selective growth of gold nanocrystals in the intermembrane space (IMS) of Escherichia coli by exploiting the electron transport chain (ETC). We systematically show that gold ions are permeated through porins in the outer membrane of E. coli and further reduced to gold nanocrystals by the ETC in live E. coli. We directly observe that the resulting gold nanocrystals exist only in the IMS by transmission electron microscopy measurements of cross-sectioned E. coli. Molecular dynamics simulations suggest that once gold ions are reduced to small nuclei by the ETC, the nuclei can be stably physisorbed onto ETC complexes, further supporting the ETC-mediated growth. Finally, we show that the ATP synthesis of E. coli where gold nanocrystals are formed in the IMS is up to 9 times higher than that of E. coli alone. We believe that our work can significantly contribute to not only improving microbial metabolic functions for biological energy conversion but also restoring physiological dysfunctions of microbial cells for biomedicine.