FLX pyrosequencing analysis of the effects of the brown-algal fermentable polysaccharides alginate and laminaran on rat cecal microbiotas

Abstract

Edible brown algae are used as major food material in Far East Asian countries, particularly in South Korea and Japan. They contain fermentable dietary fibers, alginic acid (uronic acid polymer) and laminaran (β-1,3-glucan), that are fermented into organic acids by intestinal bacteria. To clarify the effect of edible algae on the intestinal environment, the cecal microbiotas of rats fed diets containing no dietary fiber (control) or 2% (wt/wt) sodium alginate or laminaran for 2 weeks were analyzed using FLX amplicon pyrosequencing with bar-coded primers targeting the bacterial 16S rRNA gene. The most abundant phylum in all groups was Firmicutes. Specifically, Allobaculum was dominant in all diet groups. In addition, Bacteroides capillosus (37.1%) was abundant in the alginate group, while Clostridium ramosum (3.14%) and Parabacteroides distasonis (1.36%) were only detected in the laminaran group. Furthermore, rats fed alginate showed simplified microbiota phylotypes compared with others. With respect to cecal chemical compounds, laminaran increased cecal organic acid levels, particularly propionic acid. Alginate increased total cecal organic acids. Cecal putrefactive compounds, such as indole, H(2)S, and phenol, were decreased by both alginate and laminaran. These results indicate that edible brown algae can alter the intestinal environment, with fermentation by intestinal microbiota.

Fig 1

Body, cecal, and fecal weights of rats fed diets containing no dietary fiber (control), 2% (wt/wt) Na-alginate, or 2% laminaran. (A) Changes in rat body weight. (B) Endpoint cecal weights. (C) Endpoint cecal content. (D) Numbers of feces per day. (E) Amount of feces per day. Symbols: control (circles), alginate (triangles), or laminaran (squares). Values are expressed as means and SEM. *, P < 0.05; **, P < 0.01 (n = 6).

Fig 2

Cecal carbohydrates in rats fed diets containing no dietary fiber (control), 2% (wt/wt) Na-alginate, or 2% laminaran. Cecal polysaccharides (gray bars) and low-molecular-weight saccharides (white bars). Error bars indicate SEM. *, P < 0.05; **, P < 0.01 (n = 6).

Fig 3

Cecal organic acid content of rats fed diets containing no dietary fiber (control), 2% (wt/wt) Na-alginate, or 2% laminaran. (A and B) Cecal organic acid composition per gram content (A) and whole content (B). Ba, butyric acid; Pa, propionic acid; Aa, acetic acid; La, lactic acid. *, P < 0.05 (n = 6).

Fig 4

Cecal putrefactive compound levels in rats fed diets containing no dietary fiber (control), 2% (wt/wt) Na-alginate, or 2% laminaran. (A to D) Putrefactive compounds indole (A), H₂S (B), phenol (C), and ammonia (D). Error bars indicate SEM. **, P < 0.01 (n = 6).

Fig 5

Characterization of the intestinal microbiota in rats fed diets containing no dietary fiber (control), 2% (wt/wt) Na-alginate, or 2% laminaran using pyrosequencing of bacterial 16S rRNA genes. The composition of intestinal microbiota was detected at the family level. The phylum percentages are shown in each outer circle. FE, Firmicutes; BA, Bacteroidetes; AC, Actinobacteria; and PR, Proteobacteria. Additionally, each circle is separated by family level: Coriobacteriaceae (a), other Actinobacteria (b), Bacteroidaceae (c), Bacteroidales bacterium (d), Cytophagaceae (e), Marinilabiaceae (f), Prevotellaceae (g), Porphyromonadaceae (h), other Bacteroidetes (i), Clostridiaceae (j), Clostridiales bacterium (k), Eubacteriaceae (l), Lachnospiraceae (m), Lactobacillaceae (n), Lactobacillales bacterium (o), Erysipelotrichaceae (p), Oscillospiraceae (q), Ruminococcaceae (r), other Firmicutes (s), Alcaligenaceae (t), other Proteobacteria (u), and B. capillosus (*).

Fig 6

Characterization of the intestinal microbiota of rats fed diets containing no dietary fiber (control), 2% (wt/wt) Na-alginate, or 2% laminaran using pyrosequencing of bacterial 16S rRNA genes. The composition of intestinal microbiota was detected at the genus level: Enterorhabdus (a), other Actinobacteria (b), Bacteroides (c), Bacteroidales bacterium (d), Pontibacter (e), Anaerophaga (f), Parabacteroides (g), Prevotella (h), other Bacteroidetes (i), Clostridium (j), Clostridiales bacterium (k), Eubacterium (l), Lachnospiraceae bacterium (m), Lactobacillus (n), Lactobacillales bacterium (o), Allobaculum (p), Oscillibacter (q), Ruminococcus (r), other Firmicutes (s), Parasutterella (t), other Proteobacteria (u), and B. capillosus (*).