| Nanomaterial pollution and the spread of antibiotic resistance genes(ARGs) are global public health and environmental concerns. When ARGs meet with nanoparticles, how will they interact with each other? Whether nanomaterials could aid the transfer of ARGs released from dead bacteria into live bacteria to cause spread of ARGs is still unknown.To explore the horizontal transfer of drug resistance genes promoted by oxide nanoparticles. The effect of different size and concentration oxide nanoparticles on the horizontal transfer of different kind and concentration drug resistance genes into the different bacteria strains was studied by resistance selection. Results were that oxide nanoparticles especially for nano-Al2O3 could promote horizontal transfer of antibiotic-resistance genes. Compared with E.coli K12, HB101 could uptake more resistance plasmid, which was a strain easy to plasmid transformation, so we inferred NPs could aid the uptake of plasmid by transformation. Meanwhile, the promotion was consistent with the binding force, so the resistance genes might be carried into bacteria by nanomaterials, then released slowly.Here, we demonstrated that nano-Al2O3 could significantly promote plasmid-mediated ARGs transformation into Gram-negative Escherichia coli strains and into Gram-positive Staphylococcus aureus; however, bulk Al2O3 did not have this effect. Under suitable conditions, 7.4×106transformants of E. coli and 2.9×105transformants of S. aureus were obtained from 100 ng plasmid when bacteria were treated with nano-Al2O3.Nano particles concentrations, plasmid concentrations, bacterial concentrations,interaction time between the nanomaterial and bacterial cells and the vortexing time affected the transformation efficiency. We also explored the mechanisms underlying this phenomenon.Using fluorescence in situ hybridization and scanning electron microscopy, we found that nano-Al2O3 damaged the cell surface to produce pores, through which ARGs could enter bacteria. Results from reactive oxygen species(ROS) assays,genome-wide expression microarray profiling and quantitative real-time polymerase chain reactions suggested that intracellular ROS damaged the cell membrane, and that an SOS(Save Our Ship, SOS) response promoted ARG transformation.The prevalence of various antibiotic resistance genes and resistance bacterial,which is the results of use and misuse of hundreds of various antibiotics in environment, is bringing a global public health risks to human and animals. Our preliminary research found not only natural ARGs but also artificial synthetic ARGs in main chinese rivers. We also found that oxide nanoparticles in water could significantly promote conjugative transfer of ARGs mediated by the RP4, RK2 and p CF10 plasmid. However, the interaction of nanomaterial and ARGs was still unknown. Here we demonstrated that the nanoparticles protected ARGs from endonuclease degradation by Hind III, Hinc II, Sal I, Sty I, Nco I, Nde I and DNase I and acted as delivery vector for bacterial transformation by combination and high-density package. The combination and slow release were related to concentration of nanoparticles, interaction time of nanoparticles and ARGs and ions.It is suggested that the changes of ARGs molecular structure by high-density package,which is induced by nanoparticles, are the main mechanism based on ultraviolet spectroscopy, Fourier-transform infrared spectroscopy and atomic force microscopy.Besides protection ARGs from nuclease digestion, nano-Al2O3 could carry drug resistance genes to bacterial cells. In this study we show this function of oxide nanoparticles for the first time, and call it transduction. Microarray data was used to analysis genome-wide transcription, and real-time PCR was used to demonstrate the molecular mechanisms. Under suitable conditions the nano-Al2O3-p BR322 complex interacted with bacteria, 3.5×104 transformants of E. coli were obtained from 100 ng plasmid. The more drug resistance plasmid combined by nano-Al2O3, the higher transfer rate of resistance genes. The molecular mechanism of transduction might be that when transmembrane transport of nanoparticles carrying drug resistance plasmid happened, the expression of metabolic genes rdg B、gly A、pgm、acc C、deo D、pgi and asp C was downregulated for saving energy and material in cell, and the expression of pol B、rec N、ruv A、uvr B、uvr D and din G in SOS response was upregulated for the replication and expression of drug resistance genes.Oxide nanoparticles especially for nano-Al2O3 could promote horizontal transfer of drug resistance genes by transformation and transduction, and the mechanism might be oxidative damage. The ratio change of different pathways was analized by maths model. Maths model indicated: as the time passed, the transformation became more and more important.In conclusion, oxide nanoparticles could promote horizontal transfer of drug resistance genes, but the mechanism need further study. Our results indicated the environmental and health risk resulting from nanomaterials helping sensitive bacteria obtain antibiotic resistance. |
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