E. coli DH5α harbouring pET28a+ plasmid vector was lysed by alkaline lysis and the clarified plasmid solution were subjected to ultrafiltration experiment using two types of ultrafiltration membrane; i.e., cellulose generated (Ultracel) and polyethersulfome PES (Biomax). Transmembrane pressures (TMP) through vacuum suction of 0.1 to 0.7 bar were applied to the plasmid sample, and the corresponding flow rates and fluxes for both filters were investigated. Even though, these two filters showed a slight different in the flux, a marked different in DNA transmission were observed. DNA transmission were generally higher with cellulose generated filters, whereby DNA transmission by Ultracel filter was at 44.3, 63.9, 74.1, 55.6 and 54.5% at TMP of 0.1, 0.18, 0.39, 0.6 and 0.7 bar, respectively. Meanwhile, for PES filters the DNA transmission was at 22.3, 38.1, 39.1, 38.0 and 37.5% at TMP of 0.1, 0.3, 0.4, 0.6 and 0.7 bar, respectively. With the cellulose generated filter, DNA transmission reached an optimum (~70%) at about 0.6 bar after which the transmission depleted at higher TMP of 0.7 bar. Throughout all of the TMP tested, DNA transmissions were generally lower with PES filter. The properties of filter material could have contributed to the differences in DNA permeation.
Key words: Plasmid purification, membrane, plasmid flux
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