Immobilized Cells of Recombinant Escherichia coli Strain for Continuous Production of L-aspartic Acid

Abstract

For L-aspartic acid biosynthesis, high production cells of Escherichia coli mutant B-715 and P1 were immobilized in chitosan gel using a technique developed in our laboratory. The immobilization process reduced initial activity of the intact cells, however, the biocatalyst produced was very stabile for long-term use in multi-repeated batch or continuous processes. Temperature influence on the conversion of ammonium fumarate to L-aspartic acid was investigated. In long-term experiments, over 603 hours, the temperature 40 degrees C was found to be the best for both biocatalyst stability and high conversion rate. The optimum substrate concentration was 1.0 M. Continuous production of L-aspartic acid was investigated in three types of column bioreactors characterized by different volumes as well as different high to biocatalyst bed volume rations (Hz/Vz). The highest conversion rate, 99.8%, and the productivity 6 g/g/h (mass of L-aspartic acid per dry mass of cells in biocatalyst per time unit) was achieved in the bioreactor with the highest value Hz/Vz = 3.1, and liquid hour space velocity value of 5.2, defined as the volume of feeding substrate passed per volume of catalyst in bioreactor per one hour.

Emergence of nanomaterials as potential immobilization supports for whole cell biocatalysts and cell toxicity effects

“…This system has suffered low productivity [1][2][3], complex product separation [2,4], and cell lysis [5], both in wild-type (WT) and recombinant cells. Another disadvantage of a free cell system is the inability to reuse, which usually is in demand for certain applications that require cost-effective process [6].…”