Abstract: This study was devised to explore the ability of probiotics to regulate the gut microbiota in healthy, constipated and diarrheal populations. These populations were asked to ingest three different microecologics: storyose tetrahydrate (Sta), probiotics power (PP), and probiotics preparations (PPrs) at a fixed dose at fixed times daily for 6 weeks. Fresh fecal samples were collected for DNA extraction. The V3 region of the 16S rRNA gene was sequenced using Ion Torrent PGM and short- chain fatty acids (SCFAs) in feces was quantified by gas chromatography. The sequencing data was used to make diversity analysis by multivariate statistical analysis. The results showed that the most identified sequences were from Firmicutes and Bacteroidetes, accounting for 94.37% of the total number of sequences. Ingestion of probiotics significantly increased the structural diversity of intestinal flora in the tested populations. Significant growth rates were observed for the intestinal bacteria associated with SCFAs, such as Blautia and Lachnospira in the Lachnospiraceae family and Faecalibacterium and Oscillospir in the Ruminococcaceae family. Furthermore, Blautia and Faecalibacterium were positively correlated with SCFAs. In addition, changes in both the contents of SCFAs and the corresponding intestinal microbial communities were related to the composition of probiotics. Propionic acid content significantly was increased by Sta ingestion; moreover, the contents of acetic acid and butyric acid were likewise increased at about 2 weeks along with rapid and highly efficient growth of the SCFAs-producing strains for all three populations. PP caused an increase in acetic acid but led to a decreasing trend of propionic and butyric acid, accompanied by significant growth of the SCFAs-producing bacteria. After taking PPrs, the contents of acetic acid and butyric acid were significantly increased in the subjects, and the fecal content of SCFAs in constipated and diarrheal populations was close to that in healthy people. Concomitantly, the exogenous probiotics such as Bifidobacterium, Lactobacillus and Parabacteroides showed a significant increase, and the relative abundance of possible pathogenic bacteria decreased, indicating that PPrs exert greater regulation on the gut microbiota structure. In addition, enterotype analysis showed that Bacteroides and Prevotella could be adjusted driven by the diet, thus changing the enterotype, but no significant change was achieved by simply using the microecologics. In summary, the gut microbiota structure of populations with gut diseases can be adjusted toward the normal after ingestion of microecologics through increasing the bacterial community diversity and the expression of fecal SCFAs. Microecologics can sustainably inhibit harmful bacteria and promotes beneficial bacteria in the gut, thereby maintaining the stability of intestinal flora structure. The results of 16S rDNA PCR amplification and sequencing show that probiotics can change the overall structure of the intestinal flora in patients with constipation and diarrhea, and the composite PPrs are more effective than single Sta and PP.

Key words: gut microbiota, microecologics, high-throughput sequencing technology, short chain fatty acids