Interactions between Cells, Proteins, and Salts in Microfiltration of Corynebacterium glutamicum Slurry

Abstract

Interactions between cells, proteins, and salts in microfiltration of Corynebacterium glutamicum (C. glutamicum) slurry were investigated. First, dead-end microfiltration of mixed slurry of C. glutamicum cells and bovine serum albumin (BSA) was implemented at pH 4.5 and pH 7.0, where cells and BSA were oppositely and similarly charged, respectively. The rejection of BSA was observed during the course of microfiltration. According to the adsorption test, it was found that the rejection of BSA mainly resulted from the adsorption of BSA on cells, and that rejection caused by the capture within a cell cake layer or membrane accompanied with the filtrate flow was negligible. The effect of BSA addition on the average specific filtration resistance αav strongly depended on pH: αav decreased at pH 4.5 and hardly changed at pH 7.0. According to the measurements of particle size distribution and zeta potential, it was clarified that the electrostatic interaction between cells and BSA led to aggregation of cells at pH 4.5. Next, the effect of NaCl addition was investigated in microfiltration of the mixed slurry of cells and BSA. By addition of NaCl, αav was markedly influenced: αav increased at pH 4.5 and decreased at pH 7.0. It is a significant result for the improvement of the filtration performance in microfiltration of the cell slurry that αav decreased by addition of NaCl even at pH 7.0 where cells never aggregate due to an electrostatic repulsion force between cells and BSA.