Gellan gum is produced by bacterial fermentation from a pure culture of Sphingomonas elodea (formerly Pseudomonas elodea). S. elodea is a well-characterized, gram-negative, non-pathogenic bacterium that secretes a high molecular weight polysaccharide gum. Gellan gum structure is composed of repeating tetrasaccharide (4 simple sugars) units, each consisting of two glucose (Glc) residues, one glucuronic acid (GlcA) residue, and one rhamnose (Rha) residue.2 Gellan gum will form a gel in the presence of mono- or divalent cations; the latter being more efficient, e.g., calcium, magnesium; however, gellan gum (Product No. G434) is not recommended for use with DKW (9.3 mM Ca++) or other media e.g., Quoirin & Lepoivre Basal Salt Mixture containing high calcium levels as they have shown to produce a soft and cloudy gel.

Hyperhydricity is often observed when culturing plant shoots on gellan gum. It is a condition that is characterized by translucent appearance that is associated with chlorophyll deficiency, poorly developed mesophyll layers and cell walls, and high water content3 ; however, this condition can be corrected by increasing gellan gum concentration or culturing on agar gels.

Gellan gum is typically used at 2 to 4 g/L. It is suspended in medium that is room temperature or colder. Attempting to suspend it in hot medium will usually result in an incomplete, lumpy suspension that will not melt and dissolve uniformly when autoclaved. It should be added to medium after all heat-stable supplements have been added.

Store at Room Temperature.