Identification of endogenous bacteria RPB-32 of Radix pseudostellariae and its metabolites effect on intestinal microorganism community of mice

Abstract:

[Background] Intestinal microorganisms play a vital role in homeostasis of the host’s intestinal microenvironment. Many factors, such as antibiotics, diet and age, can interfere with this microbalance, causing changes in the microflora balance, which in turn affects the health of the body. There exist many pharmacological activities such as myocardial protection, immunity improvement, anti-oxidation, anti-diabetes, anti-stress, and anti-fatigue on Radix pseudostellariae. However, the regulation effect of endophytic metabolites of Radix pseudostellariae on intestinal microbes and their possible impacts on body health have not been studied so far. [Objective] The taxonomic status of endophytic bacterium RPB-32 from Radix pseudostellariae and the regulation of its metabolic extracts on the intestinal microbes of mice were studied to explore its impact on body health. [Methods] Strain RPB-32 was identified based on the traditional and molecular methods. 120 KM mice were randomly divided into four groups, viz. solvent control group (3% ethanol), the low, medium and high-dose groups of petroleum ether extract, ethyl acetate extract and n-butanol extract (n=12). After 14 days of intragastric treatments, the mice feces were collected aseptically, and the changes of intestinal microorganisms before and after intragastric gavage were detected by selective medium culture and metagenomic sequencing (solvent control (S.F.1), high-dose ethyl acetate extract group (S.F.2)). [Results] Strain RPB-32 was identified as Bacillus sp. according to the conventional and molecular methods. Compared with the blank control group, the amounts of lactic acid bacteria significantly increased in the tested groups of medium-dose ethyl acetate extracts, high-dose ethyl acetate extracts, low-dose n-butanol extracts, medium-dose n-butanol extracts and high-dose n-butanol extracts, while the amounts of Enterococcus and Enterobacter in the groups of middle-dose n-butanol extracts and high-dose n-butanol extracts were significantly reduced, respectively. The comparison of the microbial community structure showed that the amount of Firmicutes obviously reduced, but that of Bacteroidetes significantly increased in S.F.2 collated with S.F.1 at the phylum level; the amounts of Bacteroides, Prevotella, Parabacteroides, Akkermansia, Helicobacter, Butyricimonas, Alistipes, Ruminococcus, Muribaculum, Barnesiella, Odoribacter, Azospirillum, Mucispirillum, Lactobacillus obviously increased, while those of Rikenella, Angelakisella, Clostridium, Oscillibacter, Pseudoflavonifractor, Flavonifractor, Mailhella, Desulfovibrio, Faecalibacterium, Eubacterium, Lachnoclostridium, Hungatella, Butyrivibrio, Blautia, Dorea, Ruminiclostridium, Roseburia, Anaerotruncus, Butyricicoccus significantly decreased in S.F.2 contrasted with S.F.1 at the genus level; the amounts of Bacteroides sartorii, Bacteroides caecimuris, Bacteroides uniformis, Parabacteroides chinchillae, Parabacteroides glodsteinii, Helicobacter bilis, Bacteroides fragilis, Bacteroides vulgatus, Bacteroides thetaiotaomicron, Butyricimonas virosa strikingly increased, while those of Faecalibacterium prausnitzii, Rikenella microfusus, Flavonifractor plautii, Mailhella massiliensis, Clostridium clostridioforme significantly decreased in S.F.2 in comparison with S.F.1 at the species level. [Conclusion] It was preliminarily determined that the metabolites of endophytic Bacillus sp. RPB-32 (BM) from Radix pseudostellariae had the significant effects on the composition of intestinal microorganisms in mice, and might improve the degradation of glucose and lipid, anti-infective and anti-inflammatory activities in body.