Residual phosphate concentration under nitrogen-limiting conditions regulates curdlan production in Agrobacterium species

We investigated the influence of inorganic phosphate concentration on the production of curdlan by Agrobacterium species. A two-step culture method was employed where cells were first cultured, followed by curdlan production under nitrogen-limiting conditions. In the curdlan production step, cells did not grow but metabolized sugar into curdlan. Shake-flask experiments showed that the optimal phosphate concentration for curdlan production was in the range of 0.1-0.3 g l(-1). As the cell concentration increased from 0.42 to 1.68 g l(-1) in shake-flask cultures, curdlan production increased from 0.44 to 2.80 g l(-1). However, the optimal phosphate concentration range was not dependent upon cell concentration. The specific production rate was about 70 mg curdlan g-cell(-1) h(-1) irrespective of cell concentration, When the phosphate concentration was maintained at 0.5 g l(-1) under nitrogen-limiting conditions, as high as 65 g l(-1) of curdlan was obtained in 120 h.