Modulatory Effects of Tetraselmis chuii Gastrointestinal Digests on Human Colonic Microbiota

Abstract

Tetraselmis chuii is a microalga commercialized because of its richness in health-beneficial molecules. Previous studies have profusely demonstrated the biological properties of compounds isolated from T. chuii, but data are not yet available on the impact that gastrointestinal digestion could exert. This article describes the passage of T. chuii through the gastrointestinal tract, combining the INFOGEST procedure and in vitro colonic fermentation to examine potential effects on the human colonic microflora composition and its metabolic activity. Microbial plate counting was conducted to determine the different groups of microorganisms. Amplification of the 16S ribosomal RNA gene was performed via polymerase chain reaction to examine in detail the main genera of bacteria, and its metabolic activity was evaluated by measuring of short-chain fatty acids (SCFAs) by gas chromatography. The presence of T. chuii modified the fecal microbiota. Although the evolution of lactic acid bacteria and Enterococcus spp. content during 72 h showed that the use of T. chuii, compared to fructopolysaccharides such as inulin, would not provide nutritional advantages, the microalgae extract contributed to a significant decrease in Clostridium, Staphylococcus, and Enterobacteriaceae. Furthermore, T. chuii increased the relative abundance of Akkermansia and Butyricimonas, genera considered highly beneficial. In correlation with the presence of these microorganisms, the results show that the presence of T. chuii favored the release of SCFA, such as acetic (20 mM), propionic (>5 mM), isovaleric (0.3 mM), isobutyric (0.15 mM), and, mainly, butyric (>2 mM), after 72 h colonic fermentation, being indicators of gut health. These findings suggest that T. chuii has potential as a functional ingredient for promoting health through its modulatory effects on the intestinal microbiota.

Keywords: Tetraselmis chuii; butyric acid; colonic fermentation; in vitro digestion; microalgae; microflora; short chain fatty acids.

Figure 1

Progression of the effect of the non-absorbable fractions (NAFs) of Tetraselmis chuii digests and inulin on gut microbiota microbial counts (log colony-forming units (CFUs)/mL) after 0, 24, 48, and 72 h of colonic fermentation. (A) Total aerobes, (B) total anaerobes, (C) Clostridium sp., (D) Staphylococcus sp., (E) Enterobacteriaceae, (F) Enterococcus spp., (G) lactic acid bacteria (n = 3 of a pool of 5 digestions at each time). *** Differences in values were considered significant when they were higher or lower than 1 log (CFU/mL) compared to the inulin (control).

Figure 2

Effect of the non-absorbable fraction (NAF) from Tetraselmis chuii digests and inulin on α-diversity represented by Pielou’s evenness index (A,B), and Shannon index (C,D). The results are shown in box plots. * indicate significant differences compared to time zero.

Figure 3

Effect of the non-absorbable fraction (NAF) from Tetraselmis chuii digests and inulin on β-diversity represented by a principal coordinate analysis (PCoA) plot of Bray–Curtis index dissimilarity.

Figure 4

Effect of the on-absorbable fraction (NAF) from Tetraselmis chuii digests and inulin on fecal microbiota composition at phylum level at zero time and after 48 h. n = 3 (of a pool of 5 digestions).

Figure 5

Differences in relative abundance of bacteria genera between zero time and 48 h after the fermentation with NAFs from Tetraselmis chuii digests and inulin. Data are represented by effect size (log-fold change) and standard error bars. n = 3 (of a pool of 5 digestions). * p < 0.05 vs. zero time.

Figure 6

Gut microbiota composition: (A) Akkermansia, (B) Butyricimonas, (C) Bifidobacterium, (D) Bilophila, (E) Citrobacter, (F) Escherichia/Shighella at genus level of NAFs from Tetraselmis chuii digests and inulin at zero time and after 48 h. n = 3 (of a pool of 5 digestions) at each time.

Figure 7

Short chain fatty acids (mMs) throughout the colonic fermentation of the non-absorbable fractions (NAFs) of Tetraselmis chuii digests and inulin (control) at 0, 24, 48, and 72 h. (A) Total SCFA; (B) acetic acid; (C) propionic acid; (D) butyric acid; (E) isobutyric acid; (F) isovaleric acid. n = 3 (of a pool of 5 digestions) at each time. Different letters indicate statistically significant differences between results, lowercase letters refer to comparisons at different fermentation times within T. chuii or inulin samples. In contrast, capital letters refer to comparisons at the same fermentation time between T. chuii and inulin samples.