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

Abstract

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 I-1. As the cell concentration increased from 0.42 to 1.68 g I-1 in shake-flask cultures, curdlan production increased from 0.44 to 2.80 g I-1. However, the optimal phosphate concentration range was not0 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 I-1 under nitrogen-limiting conditions, as high as 65 g I-1 of curdlan was obtained in 120 h.