Fig 1.

Overexpression of the exoY glycosyltransferase in S. meliloti 1021 produces a calcofluor-bright phenotype. Binding of succinoglycan to the dye calcofluor white M2R produces fluorescence when excited with UV light. The stronger calcofluor fluorescence in the exoY overexpression strains (numbers 4, 5, and 6 in each panel) than in the control strains indicates increased succinoglycan production. The exoY overexpression strains are calcofluor bright on (A) LBMC medium after 2 days growth, (B) GMS (glutamate mannitol salts medium) after 3 days growth, and (E) Jensen's medium supplemented with glutamate and mannitol after 3 days growth. On (C) M9 minimal salts medium with ammonium chloride and sucrose as the nitrogen and carbon source, respectively, and on (D) M9 with glutamate and mannitol, growth of the exoY overexpression strains is slowed relative to growth of the control strains, and the cells do not appear to exhibit a stronger overall calcofluor signal than the control strains. All exposures were 0.5 s on a 302-nm UV light box.