Effects of Ecklonia cava subspp. kurome and stolonifera ethanolic/aqueous extracts on caecal microbiota in mice fed a high-sucrose and low-dietary fibre diet

The traditional and local edible brown algae Ecklonia cava subspp. kurome (EK) and stolonifera (ES) are rich in minerals, phlorotannins (brown algal polyphenols), and water-soluble dietary fibres (alginate, laminaran, and fucoidans). These dried powders increase not only alginate- and laminaran-degrading Bacteroides acidifaciens- and B. intestinalis-like bacteria but also Faecalibaculum. To elucidate the effect of EK and ES ingredients, other than dietary fibres, on gut microbiota, 100 mL of ethanolic/aqueous extract solutions (EK-S, ES-S; final solvent was distilled water) were prepared from 100 g of dried samples. EK-S and ES-S contained total phenolic contents of 160 and 120 μmol phloroglucinol equivalent mL^-1, respectively. A diet containing 5% (v/w) EK-S or ES-S was fed to ICR mice for 14 days. Amplicon sequencing of the 16S rDNA (V4) gene revealed that EK-S and ES-S increased Faecalibaculum abundance 2-fold and more, and this was the predominant genus (37–38%) in mice. However, the abundances of B. acidifaciens- and B. intestinalis-like bacteria did not increase. Akkermansia muciniphila-like bacteria were higher in EK-S-fed mice. Faecalibaculum and Akkermansia are regarded as desirable gut commensals correlated with anti-inflammatory and immunomodulatory effects on the host’s health. These results suggest that phlorotannins have beneficial functional effects on indigenous gut bacteria responsible for host health.