| Yogurt is one of the most popular fermented dairy products in the world,which not only provides rich nutrition for the human,but also ensures digestive health,improves immunity and gastrointestinal discomfort.However,the in-depth research on the impact and health promoting effect of yogurt or probiotics on gut microbiota is still missing,largely due to the lactic acid bacteria often survive in form of low abundance species in the human gut,which is difficult to be captured by common analysis methods.In this study,60 young volunteers were randomly divided into two groups.One group received the intervention of ordinary yogurt(fermented by Lactobacillus(L.)bulgaricus and Streptococcus(S.)thermophilus)and the other group received the intervention of probiotic yogurt fermented by ordinary yogurt starter and probiotic Probio-M8.The faeces of volunteers and questionnaire information was collected on days 0,7 and 30,and the blood indexes of volunteers at 0 and30 days were monitored.Combined with the method of intestinal low abundance species based on second-and third-generation hybrid deep metagenomic sequencing technology,the effects of the two yoghurts on gut microbiota and their potential health effects were analyzed from multiple dimensions.The main research results are as follows:(1)Based on the hybrid,deep metagenome sequencing strategy,the analysis method for gut low abundance species was constructed,which can effectively analyze the genome characteristics of low abundance species similar to lactic acid bacteria,and prove the potential importance of low abundance species in the human gut.Then,a data set including6,729 ultra-high-quality gut microbial genomes was established,which significantly improved the accuracy of metagenomic analysis of gut microbiota,enabled the characterization of Pro Bio-M8 and S.thermophilus in situ in the gut.(2)Using the constructed hybrid deep metagenomic method,the effects of two yogurts on the gut microbiota were deeply analyzed.The abundance of S.thermophilus in the gut of volunteers significantly increased after normal yogurt consumption,the abundance and growth rate of low-abundance species such as Agathobaculum butyriciproducens,Lachnospira eligens,and Clostridium tenuiflora,and significantly influenced the microdiversity of members of the Lachnospiraceae,and the abundance of bacteriophages from the Siphoviridae and Myoviridae,and abundance of gut fungi such as Aureobasidium pullulans and Candida tropicalis.Compared with normal yogurt,probiotic yogurt significantly increased the abundance and growth rate of Probio-M8 and S.thermophilus,and had a significant effect on gut fungi,while Probio-M8 and S.thermophilus had a symbiotic relationship with 21 short-chain fatty acid-producing bacteria in the gut,far exceeding the 8 symbiotic relationships of S.thermophilus in the normal yogurt group,indicating that the intake of probiotic yogurt can have additional effects on the gut microbiota,especially the potential of short-chain fatty acids producers.(3)Both kinds of yogurt significantly improved the quality of life of volunteers,in which normal yogurt significantly improved 10 mental indicators,while probiotic yogurt significantly improved 14 mental indicators and 3 defecation indicators.During the experiment,all blood indexes of volunteers were normal,but we still need to pay attention to the significant increased cholesterol and triglyceride in blood.Both kinds of yoghurt significantly increased the content of short chain fatty acids in the gut,and the contents of caproic acid and valeric acid in probiotic yoghurt group were significantly higher than those in normal yoghurt group.Based on the random forest model,a strong predictability between gut microbiota and medical indicators has been observed.Correlation analysis showed that there was a significant correlation between gut microbiota biomarkers and medical measurement indicators,indicating that yogurt consumption can affect the medical indicators of the body through multiple levels via gut microbiota.It should be noted that some medical indicators are only related to the growth rate of Probio-M8 and S.thermophilus in the gut,but not related to their abundance.These results also illustrated the importance of comprehensive analysis of gut microbiota data for understanding host phenotype data.In conclusion,this study established a set of methods for the analysis of low-abundance microbes in the human gut,based on which to understand yogurt and its microorganisms from the perspectives of gut bacterial abundance,growth rate,microdiversity,and phage and fungal abundance.The health effects produced by the strains provide a research model and data basis for better evaluation and development of probiotic yogurt,and also provide new ideas for the development of precision probiotics. |
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