Self-defense of Escherichia coli against damages caused by nanoalumina

Although studies showed effects of nanoalumina (nano-Al2O3) on Escherichia coli, no study completely provides understanding on how bacterial cells respond to damages, especially on how they initiate self-defense. In this study, we showed three types of responses of E. coli to damages caused by nano-Al2O3. Live, dead, and injured, bacteria showed improved survival rates reaching 104%, 116%, and 104% after exposure to 0.1, 1, and 10 mmol/L of nano-Al2O3 respectively. Survival rates improved from 100% to 114%, corresponding to an exposure time of 0-9 h, and from 100% to 127%, corresponding to 0-1000 μg/L Al3+. Improvements were noted in survival rates of E. coli K12 MG1655, HB101, DH5α, and K12 MG1655 △lexA treated by nano-Al2O3 in Luria-Bertani (LB) exposure system or K12 MG1655 in LB, normal saline(NS) and H2O exposure system. Bacterial cells transformed from long rods to ellipsoidal or nearly spherical as form of self-preservation mechanism; this phenomenon may be related to changes in membrane potential induced by free Al3+ released from nano-Al2O3 particles. Molecular mechanism of this response involved inhibited gene expression of sythesis and metabolism of carbohydrates, lipids and proteins. Findings presented in this study may improve understanding of potential danger of nanomaterials and control their spread to environmen.