Carrageenans (CGNs) are widely used in foods and pharmaceuticals although their safety remains controversial. To investigate the effects of CGNs and CGN-degrading bacteria in the human colon, we screened for CGN degradation by human fecal microbiota, and for inflammatory response to CGNs and/or CGN-degrading bacteria in germ free mice. Thin-layer chromatography indicated that high molecular weight (MW) CGNs (≥100 kDa) remained undegraded in the presence of human fecal microbiota, whereas low MW CGNs, i.e., κ-carrageenan oligosaccharides (KCO, ~4.5 kDa) were degraded when exposed to seven of eight human fecal samples, although sulfate groups were not removed during degradation. Bacteroides xylanisolvens and Escherichia coli isolates from fecal samples apparently degraded KCO synergistically, with B. xylanisolvens serving as the primary degrader. Combined treatment of KCO with KCO-degrading bacteria led to greater pro-inflammatory effects in the colon and rectum of germ-free mice than either KCO or bacteria alone. Similarly, p-p38-, CD3-, and CD79a-positive immune cells were more abundant in combined treatment group mice than in either single treatment group. Our study shows that KCO-degrading bacteria and the low MW products of KCO can promote proinflammatory effects in mice, and represent two key markers for evaluating CGN safety in foods or medicines.

角叉菜胶（CGN）广泛用于食品和药品中，尽管其安全性仍存在争议。为了研究 CGN 和 CGN 降解细菌在人类结肠中的影响，我们筛选了人类粪便微生物群对 CGN 的降解作用，并在无菌小鼠中筛选了对 CGN 和/或 CGN 降解细菌的炎症反应。薄层色谱表明，高分子量（MW）CGN（≥100 kDa）在人类粪便微生物群存在的情况下仍未降解，而低MW CGN，即κ-卡拉胶寡糖（KCO，~4.5 kDa）在暴露时会被降解八个人类粪便样本中的七个，尽管硫酸盐基团在降解过程中没有被去除。从粪便样品中分离的拟杆菌和大肠杆菌明显协同降解 KCO，其中解木聚糖拟杆菌是主要降解剂。 KCO 与 KCO 降解细菌的联合治疗比单独使用 KCO 或细菌对无菌小鼠的结肠和直肠产生更大的促炎作用。同样，联合治疗组小鼠中的 p-p38、CD3 和 CD79a 阳性免疫细胞比任一单一治疗组都更丰富。我们的研究表明，KCO 降解细菌和 KCO 的低分子量产物可以促进小鼠的促炎作用，并且是评估食品或药品中 CGN 安全性的两个关键标志物。