| Background and Objective With the continuous exploration of space field,manned space missions are increasing.However,during space flight,the microgravity environment in which astronauts are located can have an impact on physical health,and their risk of oral-related diseases has increased.Microbial factors are the initiating factors leading to oral infectious diseases,and supragingival plaque is closely related to the occurrence and development of common oral diseases.Supragingival plaque adheres to the tooth surface,where microorganisms interact to form a complex biological network providing an ideal site for bacterial growth and reproduction.Some studies have found that the number of certain microorganisms in the oral cavity is changed under microgravity,however the effect of microgravity on the diversity and overall structure of the oral microbial community is still unclear.Therefore,the aim of this study was to investigate the dynamic changes of plaque microbial communities on the oral gingiva of young men under simulated space microgravity conditions and to explore the effects of space microgravity environment on oral microecology.Methods In this study,16 healthy male volunteers were recruited,and supragingival plaque was collected from the volunteers using a-6°head-down bed rest(HDBR)to simulate a microgravity environment,and a total of 80 samples were obtained at five time points,namely: day1 before HDBR(AP group);during HDBR: day 5 of HDBR(BP group),day 10 of HDBR(CP group),day 15 of HDBR(DP group);and day 6 of the recovery(EP group).The bacterial genomic DNA extracted from the samples was sequenced by gene sequencing technology with amplification of the 16 S ribosomal V3-V4 high variant region,and the obtained data were analyzed for bioinformatics.Results(1)The clustering results of the supragingival plaque samples sequenced showed that a total of 4941 operational taxonomic units(OTUs)were obtained,with332,343,286,986,and 521 OTUs specific to the AP,BP,CP,DP,and EP groups,respectively.(2)Alpha diversity index analysis showed a significant increase in species richness of samples at DP group compared to the AP group(P<0.05).Beta diversity analysis showed that HDBR altered the structure of supragingival plaque microbial communities.(3)Species distribution showed that there were 15 dominant genera(relative abundance>1%)at the genus level.Compared with the AP group,the relative abundance of Corynebacterium(P<0.05)and Aggregatibacter(P<0.01)increased significantly during HDBR,while the relative abundance of of Veillonella(P<0.05),Streptococcus(P<0.01),and Lautropia(P<0.05)decreased significantly;the relative abundance of Leptotrichia increased significantly in the EP group(P<0.05),while Porphyromonas(P<0.05)and Streptococcus(P<0.01)were significantly reduced.(4)Network analysis showed that the interaction relationship between the dominant genera became simple during HDBR,and the positive and negative correlations between them changed dynamically.(5)PICRUSt analysis showed that amino acid metabolism was more abundant in supragingival plaque organisms during HDBR.Conclusion In 15-day simulated microgravity environment,the diversity,species distribution and gene function of supragingival plaque microbial community changed,which suggests that microgravity state may interfere with the balance of oral microecology,affect the stability of oral microbial community,and further lead to the occurrence and development of oral related diseases. |
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