Effects Of Polystyrene Microplastics On Intestinal Microbial Metabolism In Mic

Environmental microplastic pollution is one of the environmental issues raising serious global public health concerns.A large amount of plastic waste is produced globally every year,which is degraded into microplastics through physical,chemical,and biological reactions.Microplastics(MPs)are small plastic particles with particle size less than 5 mm.MPs not only have complex chemical structures and diverse shapes,but are also widely distributed which could exist in the environment for a long time.Polystyrene(PS)is one of the most common types of microplastics.Currently,PS-MPs have been detected in marine,land and even mammals,posing a direct or indirect health threat to living organisms.Gut microbiota plays an important role in regulating metabolic homeostasis and maintaining normal immune functions for the host.The metabolites produced by gut microbes are important substances in maintaining or regulating the healthy status of the host.Alterations in the gut microbiota are often considered as indicators of unhealthy physical conditions or diseases.In this study,we investigated the size-dependent effects of PS-MPs on the gut microbiota and its metabolic pathways in mice under the environmentally relevant concentration(100 μg/L)by ITS,16 S r RNA and shotgun metagenomic sequencing.The mice were assigned to PS0.1(0.05-0.1 μm),PS10(9-10 μm),PSMix(0.05-0.1 μm mixed with 9-10 μm)and Ctrl groups.The main findings are as follows:(1)At the genus level,Simpson index of intestinal bacteria was significantly decreased in PS0.1 groups compared with Ctrl group.Beta diversity was not significantly altered between PS-MPs treatment groups and control group.The PS0.1 and PS10 groups induced a significant reduction in beneficial bacteria and increase in opportunistic pathogens,meanwhile the PSMix group induced a significant reduction in beneficial bacteria.(2)At the genus level,Simpson index of intestinal fungi was significantly decreased in PS10 group compared with Ctrl.Beta diversity was not significantly altered between PS-MPs treatment groups and control group.PS-MPs disturbed the stability and changed the structure and predicted metabolic pathways of the fungal community in mice.The relative abundance of fungal pathogens was significantly increased,with a stronger response found in the PS0.1group.(3)The gut microbes in control group were in a state of a dynamic balance.Compared with the control group,the strong correlation between intestinal bacteria and fungi was compromised,and the gut microbial dynamic balance was disrupted.Moreover,among three PS-MPs treatment groups,PS10 had the smallest effect on the co-occurrence network of bacteria and fungi.(4)At the species level,we found that all the PS exposure groups showed a significant reduction in the relative abundance of beneficial bacteria and elevation in the relative abundance of a few pathogenic bacteria.Moreover,PS-MPs with different sizes had different effects on gut microbiota in mice.Compared with PS10 group,more pathogens were significant altered in PS0.1 group.PS-MP with 0.05-0.1μm in diameter played a dominant role in the health effects induced by PSMix group.(5)The relative abundance of antibiotic resistance genes and virulence factors was significantly altered.For instance,PS exposure significantly increased the relative abundance of genes encoding tetracycline antibiotic resistance,suggesting that the mice were resistant to tetracycline antibiotics after the PS exposure,which might be a threat for the health of the host when certain treatment is needed for some diseases.(6)PS-MPs affected the relative abundance of various metabolic pathways in mice,including pathways involved in biosynthesis,energy metabolism and degradation/ utilization/assimilation.The metabolites produced by the gut microbiota play a key role in the healthy status of the host,such as short-chain fatty acids,unsaturated fatty acids,essential amino acids,and vitamins.The relative abundance of pathways involved in the biosynthesis of these metabolites was significantly reduced,which might influence metabolic homeostasis of the host.In conclusion,PS-MPs disrupted the dynamic balance of gut microbiota and its metabolic pathways in mice,increased resistance to tetracycline antibiotics,and posed a threat to the host.The effect of PS on gut microbiota was in a size-dependent manner,with stronger effect observed in PS-MP with 0.05-0.1 μm in diameter.