Abstract: Objective: To explore the role of the probiotic strain Lactobacillus helveticus TS206 in regulating the intestinal microflora in mice and to unravel the mechanisms by which probiotics can maintain intestinal flora homeostasis. Methods: Male BALB/c mice were divided into probiotic, control and blank groups. The probiotic and control groups were respectively gavaged with L. helveticus suspension and an equal volume of normal saline once a day for 7 consecutive weeks, respectively. The blank group did not receive gavage. Stool samples were collected every week for extracting genomic DNA by means of a commercial kit. The V6 variable region of the 16S rRNA gene was subjected to highthroughput sequencing by using the Ion torrent personal genome machine system and the obtained data were analyzed using bioinformatic tools and multivariable statistical analysis. Results: All sequence reads were delineated into 1 617 operational taxonomic units (OTUs) at a 97% similarity level, belonging to 8 major bacterial phyla, with Firmicutes and Bacteroidetes being the dominant ones in all groups, accounting for 97.49% of the total number of sequences, among which Firmicutes showed the highest abundance of more than 70%. The strain S24-7, Lachnospiraceae, Ruminococcaceae, Rikenellaceae, and Bacteroidaceae were the dominant bacterial families, and the Enterobacteriaceae population in the probiotic group was lower than in the control group and fell during the administration period. Totally 53 key OTUs were significantly associated with the bacterial community structure in the intestine of the two groups of mice as determined by linear discriminant analysis effect size (LEfSe) analysis, of which, 27 OTUs were enriched in the control group, belonging to Enterobacteriaceae, Ruminococcaceae, Lachnospiraceae and Clostridium, and 26 OTUs in the L. helveticus TS206 group, belonging to Clostridium, whose abundance level was higher than in the control group, Lachnospiraceae and Bacteroides. Principal component analysis showed that the fecal microbial communities of the probiotic group were completely separated from those of the control group. Overall there were significant differences in the structure of intestinal flora between the two groups, and the OTUs in the groups showed a negative correlation. Conclusion: L. helveticus TS206 can change the structure of intestinal flora, inhibiting the growth of harmful microbes, promoting the proliferation of beneficial bacteria proliferation and consequently maintaining the structure of the intestinal flora at a steady state.

Key words: Lactobacillus helveticus TS206, gut microbiota, Ion torrent personal genome machine sequencing technology, bioinformatics, multivariate statistical analysis