Isolation and preliminary characterization of a glucan-type exopolysaccharide produced by Bacillus tequilensis strain HH from Egyptian fermented cucumber.

Exopolysaccharide (EPS) production is a common feature of microbial carbohydrate metabolism during fermentation; however, glucan-type EPS produced by Bacillus species in fermented vegetable systems remain insufficiently characterized. This study aimed to isolate an EPS-producing bacterium from naturally fermented cucumber and to perform a preliminary physicochemical and spectroscopic characterization of the produced polymer. An EPS-producing bacterial isolate was recovered and identified as Bacillus tequilensis, a member of the Bacillus subtilis species complex, based on 16 S rRNA gene sequence analysis. The extracellular polysaccharide was partially purified and analyzed using FTIR and ¹H NMR spectroscopy, revealing structural features consistent with a glucan-type EPS. Rheological analysis demonstrated a concentration-dependent increase in viscosity, confirming the macromolecular nature of the polymer in aqueous systems. Sucrose-hydrolyzing activity was detected under optimized conditions, indicating active carbohydrate metabolism associated with EPS production. In vitro cytocompatibility assessment using Vero and WI-38 cell lines showed high cell viability at low to moderate concentrations, with a dose-dependent reduction observed at higher levels. Overall, this study reports the isolation of an EPS-producing Bacillus tequilensis strain from Egyptian fermented cucumber and provides preliminary insights into the properties of its glucan-type exopolysaccharide, highlighting fermented vegetable microbiota as a potential source of functional biopolymers.