The Examination of Seliberia stellata Exopolymers Using Lectin Assays

Holdfast exopolymers of the dimorphic oligotrophic bacterium Seliberia stellata were examined using fluorescent lectins under light microscopy and colloidal gold lectins using transmission electron microscopy. Examination using fluorescent-labeled lectins revealed that lectins specific for polysaccharides and monosaccharides such as glucose and/or mannose, galactose, N-acetylgalactosamine, and N-acetylglucosamine (and its dimer) adhered to holdfast structure. Colloidal gold-labeled lectin assays also suggested the presence of these sugars. Both the holdfast that mediates swarmer cell adhesion and the holdfast that facilitates rosette formation gave similar results, suggesting the structures may be the same. Another exopolymer produced later in the growth cycle was observed using transmission electron microscopy. It appeared as an amorphous glycocalyx-like material very different from holdfast exo-polymers. Retention of the gold lectin (Wheat Germ Agglutinin (WGA), suggested the presence of N-acetylglucosamine, but fluorescent analyses were unsuccessful. The data suggest that S. stellata produces at least two different exopolymers: (a) the exopolymer of the swarmer cell and rosette holdfast whose function is adhesion and whose composition is (but may not be limited to) polysaccharides and (b) a slime-like exopolymer whose composition and function remain unknown.