Holdfast exopolymers of the dimorphic oligotrophic bacterium Seliberia
stellata were examined using fluorescent lectins under light microsco
py and colloidal gold lectins using transmission electron microscopy.
Examination using fluorescent-labeled lectins revealed that lectins sp
ecific for polysaccharides and monosaccharides such as glucose and/or
mannose, galactose, N-acetylgalactosamine, and N-acetylglucosamine (an
d its dimer) adhered to holdfast structure. Colloidal gold-labeled lec
tin assays also suggested the presence of these sugars, Both the holdf
ast that mediates swarmer cell adhesion and the holdfast that facilita
tes 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 a
n amorphous glycocalyx-like material very different from holdfast exop
olymers. Retention of the gold lectin (Wheat Germ Agglutinin (WGA), su
ggested 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 exopo
lymer whose composition and function remain unknown.