| Nanotechnology has been widely used in the field of medicine,and some nanomaterials will enter the human digestive system and exist in the symbiotic microbiota of the human gut,playing an important role in human health and disease.A large number of antibacterial activity experiments have shown that nanomaterials have good antibacterial properties,so the nanomaterials entering the human gut may affect the human gut flora and its health.Lactobacillus casei(L.casei),one of the beneficial bacteria in the human intestinal flora,belongs to anaerobic bacteria and can secrete acidic metabolites.Studies have shown that the entry of nanomaterials into animals,including humans,can cause changes in the composition and distribution of the gut microbial community of organisms,and these changes are directly or indirectly related to the occurrence of certain inflammatory responses and diseases.However,the current research on the toxicological effects of nanoparticles on gut bacteria mainly focuses on enriching nutrients in vitro,and cannot represent the toxicological effects of nanoparticles on gut microorganisms in the real intestinal environment(including the composition of the medium and the content of oxygen).This study took the model organism L.casei as the research object,and established the growth conditions and characteristics of L.casei in the physiological simulated fluid by simulating the composition of human intestinal fluid and the hypoxia and anaerobic conditions in the intestinal tract.To explore the toxicological effects of medical nanomaterials on L.casei by measuring the growth and metabolism of two commonly used medical-related artificial nanomaterials,namely silver nanoparticles(Ag NPs)and hyaluronic acid-modified gold nanoparticles(HA-Au NPs).Furthermore,the fate of nanoparticles after co-incubation with culture medium was studied by means of UVvisible spectroscopy,inductively coupled plasma mass spectrometry,and gel electrophoresis.The research results obtained are as follows:(1)L.casei has completely different growth patterns in the two media MRS and IF.The rich medium MRS contains sufficient carbon and nitrogen sources.Under the same conditions,the specific growth rate of L.casei in MRS much higher than IF.Furthermore,L.casei prefers to grow in anaerobic conditions compared to aerobic conditions.(2)Parts of the metabolism of bacteria were affected by exposure to non-growth inhibitory concentrations of nanomaterials,and the expression of bacteriocin-related genes of lactic acid bacteria was inhibited when Ag NPs and HA-Au NPs exposed to low concentrations were detected at the molecular level.(3)The content of silver ions released by Ag NPs under anaerobic conditions is much lower than that in aerobic conditions,but there is no significant difference in the content of leached gold ions from HA-Au NPs under aerobic and anaerobic conditions.(4)After incubating the nanoparticles with an acidic medium containing bacterial products,it was found that the nanoparticles were more likely to agglomerate in the medium than in water.After co-incubation with the culture medium,the changes in the hydrodynamic size,surface protein and metal ion concentration of the nanoparticles were measured,indicating that the peptides and proteins in the culture medium would be adsorbed on the nanoparticle surface.The results of gel electrophoresis showed that the molecular weight of some proteins adsorbed on the surface of nanoparticles was consistent with the molecular weight of bacterial metabolites,which further clarified the influence of environmental media on the properties of nanoparticles themselves.This study investigated the toxicological effects of Ag NPs and HA-Au NPs on L.casei under aerobic and anaerobic conditions.In addition,through the co-incubation of nanoparticles with medium containing bacterial metabolites,the changes in the physicochemical properties of nanoparticles in physiological medium were explored,which provided more evidence for exploring the toxicity mechanism of nanoparticles. |
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