Efeitos da biomassa de microalgas dulcícolas sobre a microbiota colônica de adultos saudáveis em sistemas de fermentação in vitro

Abstract

Microalgae are photosynthetic microorganisms capable of accumulating several bioactive compounds with prebiotic potential, however, this functional property is little explored. The present study sought to evaluate the prebiotic effects of freshwater microalgae biomass, using in vitro fermentation systems.The present study sought to evaluate the prebiotic effects of freshwater microalgae biomass, using in vitro fermentation systems.Initially, four freshwater microalgae species (Chlorella vulgaris, Desmodesmus maximus, Chlorococcum sp cf hypnosporum and Spirulina platensis)were cultivated to obtain the integral biomass. The biomasses were characterized in terms of chemical composition and submitted to the simulated digestion process. Posteriorly, the intestinal phase was lyophilized and used for fermentation assays with human fecal inoculum compared to fructooligosaccharides (FOS) as a positive control. After 24 and 48 h of fecal fermentation, changes in the relative abundance of specific groups of the fecal microbiota were evaluated using in situ hybridization fluorescence coupled to flow cytometry. Furthermore, the indicators of bacterial metabolic activity (pH, sugars and organic acids) were measured and the prebiotic score of each microalgae was determined. The results revealed that the biomass of S. platensis showed higher concentrations of nystose (3.71 g/100g) and raffinose (6.14 g/100g), while D. maximus had higher concentrations of insoluble fiber (42.60 g/100g) and kestose (110.62g/100g). The highest concentrations of monosaccharides (glucose and fructose) and rhamnose were identified in C. vulgaris (16-52 g/100g), while C. sp cf hypnosporum showed high concentrations of procyanidin A2, hesperidin and kaempferol-3-glycoside. Digested biomass and FOS increased the relative abundances of Lactobacillus, Enterococcus and Bifidobacterium, while reducing Bacteroides spp./Prevotella spp, Clostridium histolyticum and Eubacterium rectale-Clostridium coccoides present in the fecal microbiota. The microbial metabolic activity differed between the biomasses, FOS and the time evaluated. After 48 h of fermentation, all microalgal biomasses showed variable prebiotic indices (7.16-11.29) and higher than FOS (4.67).In the second stage of this research, the digested biomass of S. platensis (0.5 mg/mL) was evaluated for its ability to stimulate the proliferation and metabolism of L. acidophilus (La-5) during cultivation in laboratory medium for 72 h. Subsequently, 1.5g of digested biomass of S. platensis was administered in combination with La5 (106 CFU/g) in the Intestinal Microbial Ecosystem Simulator (SEMH®), for five days to evaluate the effects on the composition of the fecal microbiota of healthy medium-aged individuals. L. acidophilus at the same concentration was also evaluated separately. During fermentation, the digested biomass of S. platensis had a higher impact (9-8.28 log/CFU) than FOS (8.74-8.05 log/CFU) on the rate of cell proliferation and synthesis of La-5 metabolites in laboratory medium, reducing the pH of the medium and increasing the production of acetic, lactic and propionic acid.Biomass of S. platensis in combination with La-5 (Spi-La5) increased the abundanceof Erysipelatoclostridium, Roseburia, Enterococcus, Bifidobacterium, Coriobacteriaceae UCG-003, Enterobacter andParaclostridium. On the other hand, isolated administration of L. acidophilus (La5) increasedBacteroides, Megasphaera, Lactobacillus, Parabacteroideand reduced ammonium ions compared to Spi-La5.These results show the prebiotic potential of whole freshwater microalgae biomass as evidenced by changing the composition, diversity and metabolic activity of the human gut microbiota and suggest the use of S. platensis biomass in combination with La-5 as a strategy to modulate the microbiota in healthy adults.