An exopolysaccharide (EPS) synthesizing potentially probiotic Gram-positive bacterial strain was isolated from fish (Tor putitora) gut, and its EPS was structurally characterized. The isolate, designated as FW2, was identified as Lactobacillus reuteri through 16S rRNA gene sequencing and phylogenetic analysis. This isolate produces fructan-type EPS using sucrose as a substrate. Based on ¹³C-NMR spectroscopy, methylation analysis and monosaccharide composition, the EPS was identified as a linear levan polymer with fructose as main constituent linked via β(2 → 6) linkages. Based on molecular weight (MW) distribution, two groups of levan were found to be produced by the isolate FW2: one with high MW (4.6 × 10⁶ Da) and the other having much lower MW (1.2 × 10⁴ Da). The isolate yielded about 14 g/L levan under optimized culturing parameters including aeration conditions, pH, temperature and substrate concentration. The obtained bimodal molecular weight linear levan is the first of its type to be synthesized by a L. reuteri isolate from fish gut. Bimodal molecular weight prebiotic levan together with the probiotic potential of the producing strain would provide a new promising synbiotic combination for use in aqua culture.

从鱼 ( Tor putitora ) 肠道中分离出一种合成潜在益生菌革兰氏阳性菌株的胞外多糖 (EPS) ，并对其 EPS 进行了结构表征。该分离株命名为FW2，通过16S rRNA基因测序和系统发育分析鉴定为罗伊氏乳杆菌。这种分离物使用蔗糖作为底物产生果聚糖型 EPS。基于¹³ C-NMR 光谱、甲基化分析和单糖组成，EPS 被鉴定为以果糖为主要成分通过 β(2 → 6) 键连接的线性多聚体。根据分子量 (MW) 分布，发现分离株 FW2 产生了两组果聚糖：一组具有高分子量 (4.6 × 10 ⁶ Da) 和另一个具有低得多的 MW (1.2 × 10 ⁴  Da)。在包括通气条件、pH、温度和底物浓度在内的优化培养参数下，分离物产生约 14 g/L 的左旋糖醇。获得的双峰分子量线性果聚糖是第一个由鱼肠中的罗伊氏乳杆菌分离物合成的同类产品。双峰分子量的益生元果聚糖与生产菌株的益生菌潜力将提供一种新的有前途的合生元组合，用于水产养殖。