| Formaldehyde is an important industrial product that exists in either gas or solution states.It enters the body through the respiratory or digestive system.Many studies have shown that air formaldehyde can cause pathological symptoms,including acute poisoning symptoms and chronic toxic symptoms,especially cancers that harm to human health.Although there are many studies on effects of air formaldehyde inhalation on human health through the respiratory tract,the study on the intake of formaldehyde through the digestive tract is rare.Intestinal microflora has attracted lots of scientists in recent years.There have been a number of studies on the relationship between the intestinal microflora and health,especially the changes with the intestinal microflora,which can lead to many diseases.Environmental pollutants entering the digestive tract and will firstly interact with the intestinal microflora,and then affect health.Up to date,only a few studies have shown that environmental pollutants can affect the intestinal microflora.Therefore,exploring the interaction"between formaldehyde and intestinal microbiota is not only helpful in understanding the mechanism of formaldehyde in affecting the digestive system,but also complementing and extending the existing studies.It is also helpful in understanding the relationships between intestinal microflora and human health.In this dissertation,mice were used as a research model to study the dose and time effects of formaldehyde on the mouse digestive system.The research methods included traditional microbial isolation and culture methods,and 16S rRNA genes high-throughput sequencing and metagenomic methods.For the sequence data obtained,as well as the microbial microflora data generated,further statistical analysis and statistical comparison using software such as STAMP.The important results obtained are as follows:Firstly,a preliminary study was performed on the changes of intestinal micro:flora in mice before and after the treatment of formaldehyde treatment by microbiological culture.The results showed that after the mice receiving formaldehyde treatment,no significant changes in the culture characteristics of the intestinal flora were observed.The typical colonies of intestinal microflora in mice receiving formaldehyde treatment were analyzed by 16S rRNA genes sequencing after cultivation by using different medium and different culture methods(aerobic culture and anaerobic culture).The effective sample data,by Blast analysis,17 bacteria were found,most of which were bacteria of Bacillus Bacillus.These results indicate that in vitro culture methods are conducive to the growth of individual bacteria.Therefore,due to the complexity of intestinal microflora in mice and the defects of in vitro culture methods,it is difficult to accurately reveal the changes of intestinal microflora in mice after formaldehyde treatment,affecting further interpretation and related application researchSecondly,by using 16S rRNA genes high-throughput sequencing combined with metagenomic analysis technology,formaldehyde-mediated changes in intestinal microflora in mice were studied.It was initially revealed that when formaldehyde can cause symptoms of poisoning in mice,formaldehyde treatment for intestinal bacteria has the dose effects and time effects.Using high-throughput sequencing,the abundance and distribution of mouse intestinal bacteria were obtained at the level of phylum,families,and genera.The results showed that the relative abundance of Bacteroidetes and Firmicutes bacteria in all groups far exceeded 1%,which was the dominant bacteria class.Both of them exceeded the 95%of total number of gut bacteria,is far more than the rest of the bacteria and is in an absolute dominant position.Using STAMP statistical analysis and heat map combined with cluster analysis,the changes of intestinal bacterial abundance caused by formaldehyde treatment were analyzed.The PICRUSt program was then used to predict the effect of formaldehyde treatment on the function of the intestinal microflora in mice in order to reveal the dose and duration of formaldehyde treatment that can cause significant poisoning in mice.The results showed that formaldehyde induction could not fundamentally affect the structure and composition of intestinal microflora in mice,but it can induce significant changes in the relative abundance and diversity of intestinal microflora,especially in the taxonomic and family classification levels.The relative abundance and diversity of bacteria have changed significantly.The bacteria that are affected include not only the dominant families in the intestinal microflora,but also the genus bacteria,as well as rare families and genus bacteria.By predicting KEGG metabolic pathways and correlation analysis,it was found that formaldehyde induction can cause a series of related detoxification metabolic pathways and signal pathway changes in the intestinal microflora.Thirdly,after short-term(7 or 14 days)and lower doses of formaldehyde exposure,the mice have not developed symptoms of significant poisoning or only mild symptoms of poisoning,the 16S rRNA high-throughput sequencing results showed that intestinal microflora in mice was relatively stable after 7 days of formaldehyde treatment or 14 days of formaldehyde treatment.Using STAMP statistical analysis and heat map combined with cluster analysis,several bacterial being senstive to formaldehyde treatment were detected including Prevotella,Streptococcus,Lactococcus,Candidatus Arthromitus,Delftia.It is speculated that there is a certain repair or stress mechanism,which can protect the intestinal microflora of mice and resist the effect of early low dose formaldehyde,however,with the prolongation of formaldehyde action time,this protective mechanism is suppressed or lost,resulting in intestinal microflora damage.Finally,the present study also found that the effect of physiological saline can lead to changes in the relative abundance of intestinal microflora in mice,and detected several bacteria that were affected by physiological saline at the level of gate and genus classification.Since this change is relatively stable,it can be speculated that after saline treatment,the intestinal microflora of mice can be in a relatively stable state.This finding provides guidance for future research on the changes of intestinal microflora induced by environmental pollutants.In summary,this study explored the effects of formaldehyde exposure on intestinal microflora in mice and firstly provided the data on the effects of formaldehyde impact on the structure and abundance of intestinal microflora in mice.The results of the study showed that although there was no fundamental change in the structure and composition of the intestinal microflora,formaldehyde exposure had an impact on the relative abundance of intestinal micro:flora,and identified a number of dominant bacteria,common bacteria,rare bacteria and bacteria that were affected by formaldehyde treatment,and have expanded their research fields in the field of formaldehyde toxicology,providing guidance for further research on formaldehyde,intestinal bacteria,and human health. |
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