Ecklonia cava subsp. kurome and E. cava subsp. stolonifera can aid regulation of gut microbiota in mice fed a high-sucrose and low-dietary fibre diet

Ecklonia cava subsp. kurome (EK) and E. cava subsp. stolonifera (ES) are rich in phlorotannins and water-soluble polysaccharides (alginates, laminarans and fucoidans). Total phenolic content (TPC), antioxidant (O-2(-) radical scavenging and Fereducing) and anti-glycation (bovine serum albumin-fructose model) capacities of dried EK and ES were higher than those of Eisenia bicyclis and Eisenia nipponica in vitro (p < 0.05). To clarify the effect of EK and ES on gut microbiota, 5% (w/w) EK or ES was administered to Institute of Cancer Research mice fed a high-sucrose and low-dietary fibre diet for 14 days and their caecal microbiota was analysed using 16S rDNA (V4) amplicon sequencing. The amplicon sequence variant (ASV) numbers of the EK and ES groups were 4- and 2-fold lower than those of the no fibre (NF) diet group. Bacteroidota containing alginate- and laminaran-degrading microbes, such as Bacteroides acidifaciens- and B. intestinalis-like bacteria, were more abundant in EK and ES groups than in the NF group. Faecalibaculum rodentium- and Akkermansia muciniphila-like bacteria were also more abundant in EK and ES groups than in the NF group. These EK- and ES-responsive indigenous gut bacteria have been regarded as beneficial commensal for host health. Further studies on EK and ES including investigation of dose-dependent effects are needed.