Mechanisms for biopolymer accumulation in immobilized Acinetobacter calcoaceticus system

The gram-positive bacteria, Acinetobacter calcoaceticus, is capable of accumulating biopolymer in the carrier matrix of an immobilized cell system. Several possible mechanisms for the biopolymer accumulation are evaluated. It appears that direct solid surface polymer adsorption and polymer diffusion limitation within the pore space are minor factors in biopolymer accumulation. Calculations demonstrate that the cell bound polymer to dry cell weight ratio is much higher for immobilized cells than for free cells. The higher cell-bound polymer to dry-cell-weight ratio for immobilized cells as well as the accumulation of the immobilized cells in the Celite matrix are believed to be the main factors for biopolymer accumulation in the Carrier matrix. Further studies reveal that the cell-bound polymer to dry-cell-weight ratio is strongly affected by shear forces. At zero shear stress, such as would be present in the carrier matrix, cell bound polymer to dry cell weight ratio can be as high as 1.6. As the shear stress increases, this ratio decreases. When shear stress increases above 5 dyn/cm(2), a level equivalent to the shear experienced by free cells in a stirred tank fermentation, cell-bound polymer decreases to less than 20% of dry cell weight. A macroscopic model is developed to describe the effect of shear stress on the cell-bound polymer to dry-cell-weight ratio.