Effects Of Food Additive Nanomaterials On The Growth And Metabolism Of A Human Commensal Bacterium

With the widespread use of nanotechnology in the food industry,the exposure of people to food additive nanomaterials through their diet has increased significantly.These food additive nanomaterials,when ingested through the human oral cavity,come into contact with commensal bacterium that survive in the human digestive system,and commensal bacterium play an important role in human health and disease.Therefore,the interaction between food additive nanomaterials and human commensal bacterium and their biological effects deserve attention and study.In this work,artificial saliva was used to simulate exposure conditions close to the human oral environment to study the effects of different food additive nanomaterials on the growth and metabolism of Streptococcus salivarius K12 in different physiological conditions,as well as the physicochemical transformation of the bacterial-induced nanomaterials and the interaction relationship between them.The results showed that:（1）In aerobic and anaerobic conditions,the growth of Streptococcus salivarius K12 was not significantly affected by food additive nanomaterials in the rich growth medium THB.In artificial saliva,Ag NPs significantly inhibited the growth of bacteria and showed a dose-dependent effect,with 100%inhibition at 100 mg/L Ag NPs.This may be due to the high protein content in the rich growth medium THB and the reduced bioavailability of silver ions released from Ag NPs after binding to proteins.（2）The effect of food additive nanomaterials exposure on the competitiveness of Streptococcus salivarius K12 bacteriocins was assessed by testing the gene expression and antimicrobial activity of the metabolite bacteriocins of Streptococcus salivarius K12.Nanomaterial exposure（6 h）in rich growth medium THB,in aerobic conditions resulted in upregulation of gene expression of the Streptococcus salivarius K12metabolite bacteriocin,while the opposite result was observed in anaerobic conditions.And in aerobic conditions,short-time（1 h）exposure of nanomaterials downregulated the expression of bacteriocin gene,while long-time（18 h）exposure increased gradually upregulation.In addition,bacterial inhibition zone diameter measurements showed that short-time exposure had almost no effect on the antibacterial activity of Streptococcus salivarius K12,but prolonged exposure significantly stimulated the antibacterial activity.Consistent with the gene expression results,changes in gene expression were accompanied by an increase in bacterial antimicrobial activity.（3）Characterization of Streptococcus salivarius K12 after transformation in artificial saliva in aerobic conditions revealed that the food additive nanomaterials interacted with the bacterial metabolite bacteriocins and nutrients in the culture medium.Bacterial metabolites secreted in artificial saliva during growth markedly affected the transformation of NPs compared to artificial saliva not containing metabolites.The transformations included significant agglomeration,association with proteins and increased bioavailability of Si O₂NPs,Ti O₂ NPs and food additive Ti O₂,while Ag NPs became less toxic.In the same conditions,all four food additive nanomaterials exposed to 100 mg/L transformation significantly inhibited the growth of Streptococcus salivarius K12,further demonstrating that the interaction between the two produced a more virulent transformation product.In conclusion,this study showed that food additive nanomaterials can affect beneficial bacterial traits needed for competitiveness in microbiota and bacterial metabolites transform food additive nanomaterials,potentially affecting the fate and toxicity of food additive nanomaterials in the digestive tract.