Increased bacterial uptake of macromolecular substrates with fluid shear

Abstract

To investigate the effect of fluid shear on uptake rates of low diffusivity macromolecular substrates by suspended cultures, I measured the radiolabel and oxygen uptake of two model compounds, bovine serum albumin and dextran, in pure cultures of Zoogloea ramigera and E. coli, respectively. Oxygen utilization rates of stirred samples grown on BSA and dextran were 2.3 and 2.9 times higher, respectively, than undisturbed (still) samples. Uptake rates of (3H) BSA and (3H) dextran by stirred samples were 12.6 and 6.2 times higher, respectively, than still samples. These experimentally obtained increases are larger than increases predicted using a mass transfer model. The mass transfer model predicts uptake rate will increase by a factor of 1.6 and 1.8 for BSA and dextran, respectively, as a result of stirring. Uptake rates of low-molecular-weight substrates with high diffusivities, such as leucine and glucose, were only slightly affected by fluid shear. Since macromolecules can comprise a major portion of bacterial substrate in engineered, laboratory, and natural systems, the demonstrated effect of fluid shear has wide implications for the evaluation of engineered bioreactors used for wastewater treatment as well as for kinetic studies performed in basic metabolic research.