Novel gelling agent similar to galactomannan from the sheath-forming bacterium Sphaerotilus hippei

Aims Hydrogels have applications as food additives and cosmetics, as well as medical applications such as the drug delivery and scaffolding materials for cells. There is high demand for new hydrogels that can facilitate technological innovation. Here, we report a galactomannan-like gelling agent (hydrogel) produced by the sheath-forming bacterium Sphaerotilus hippei. Methods and Results S. hippei was grown on glucose and tuna extract. The presence of a microtube-shaped sheath with a closed end was confirmed using electron microscopy. The sheath was prepared by treatment with sodium dodecyl sulphate and NaOH. Chemical composition analysis and nuclear magnetic resonance (NMR) spectroscopy revealed that the sheath is an assemblage of a polysaccharide with a tetrasaccharide repeating unit composed of β-d-Galp, α-d-Manp, and β-d-Manp in the molar ratio of 2:1:1. Molecular simulations suggested a right-handed helical structure with 16 sugar residues per turn and a pitch of 4.0–5.0 Å. A hydrogel was formed by solubilization of the sheath in hot water and subsequent cooling. Conclusions The sheath of S. hippei is a closed-ended microtube assembled with galactomannan-like polysaccharide, which may have a helical conformation. The sheath has hydrogel-forming capabilities.