Nano-Al2O3 particles affect gut microbiome and resistome in an in vitro simulator of the human colon microbial ecosystem

Nano-Al2O3 has been widely used in various consumer products and water treatment processes because of its unique physicochemical properties. The probability of human exposure to nano-Al2O3 increases significantly, of which oral ingestion is an important route. However, effects and underlying mechanisms of nano-Al2O3 on gut microbiota and resistome are still not well delineated. Here, we systematically investigated the effects of nano-Al2O3 on the human gut microbiome by an in vitro simulator of human colon microbial ecosystem. Results indicated that nano-Al2O3 interfered with the gut microbiota, and significantly suppressed the short-chain fatty acids metabolism, which might pose adverse effects on the host. More seriously, high level of nano-Al2O3 (50 mg/L) was more destructive to the gut flora, though the damage might be temporary. In addition, sub-inhibitory low-dose of nano-Al2O3 (0.1 mg/L) significantly enhanced the abundance of antibiotic resistance genes (ARGs) after 7-day exposure. This is attributed to that low concentration of nano-Al2O3 can promote horizontal transfer of ARGs by increasing cell membrane permeability and relative abundance of transposase (e.g. tnpA, IS613, and Tp614). Our findings confirmed the adverse effects of nano-Al2O3 on the human gut resistome and emphasized the necessity to assess potential risks of nanomaterials on the human gut health.