Fermentation of Structurally Defined Alginate Oligosaccharides by the Human Gut Microbiota Enriched in Bifidobacterium, Bacteroides, Faecalibacterium, or Blautia

Alginate oligosaccharides (AOS) are attractive candidates for prebiotic development, yet how oligosaccharide structure and baseline microbial community composition interact to shape fermentation remains an open question. In this study, we stratified fecal microbiota from healthy donors into operational genus-predominance groups (Bifidobacterium, Bacteroides, Faecalibacterium, or Blautia) and selected representative samples for in vitro fermentation of six structurally distinct AOS preparations (SAOS-1, SAOS-2, OAOS, UAOS, SMOS, and SGOS). Substrate consumption, short-chain fatty acid (SCFA) production, and shifts in microbial community structure were profiled. The six preparations differed in structural type, number-average molecular weight, and average degree of polymerization. Among them, SAOS-1 exhibited the most consistent utilization across all four groups and yielded the highest total SCFA production. SAOS-1 fermentation also attenuated inter-group community divergence and enriched several beneficial or functionally relevant taxa, including Bacteroides and Faecalibacterium. Interestingly, the magnitude and direction of microbial responses remained enterotype-dependent, with the Bacteroides-predominant group assembling the most complex fermentative consortium. These findings demonstrate that AOS structure and baseline microbial ecology jointly dictate fermentation outcomes, positioning SAOS-1 as a strong candidate for precision prebiotic development. This structure–community interaction paradigm provides a rational basis for the targeted deployment of marine oligosaccharides in personalized gut health strategies.