Production of the commercially available polysaccharide curdlan by Agrobacterium sp. strain ECP-1, isolated as a mutant strain from ATCC 31749, on a medium containing a hydrolysate of the plant prairie cordgrass with selected ammonium phosphate concentrations was investigated for a period of 144 h. Although several ammonium phosphate concentrations supported curdlan production by the strain, the optimal concentration after 120 or 144 h was 3.3 mmol·L⁻¹. Only ammonium phosphate concentrations of 1.1 or 8.7 mmol·L⁻¹ failed to support curdlan production by the strain after 120 or 144 h. Biomass production by strain ECP-1 on the hydrolysate-containing medium after 120 or 144 h was comparable, independent of the ammonium phosphate concentration present. The curdlan yield from the cordgrass hydrolysate indicated that the grass was an effective plant biomass substrate for polysaccharide production.