Bioprocess development for thermostable glucose isomerase production

Angardi, Vahideh
In this study, process development for glucose isomerase (GI) was aimed. In this context, firstly, thermostable xyl genes, PCR amplified from Thermus thermophilus and Pyrococcus furiosus cells, were recombined to the E.coli BL21 (DE3) and P.pastoris strains, respectively. But significant increase in the term of GI activity compared with wild type cells only detected in recombinant E.coli strain so this strain was selected for further experiments. Then, the effect of different natural and artificial inducers on the production of rGI under control of LacUV5 promoter was investigated in laboratory-scale bioreactors. Lactose was shown to be more efficient in the term of operon induction for long time bioprocesses. Thereafter, in order to increase thermostable rGI production rate, to achieve high cell density culture of E.coli BL21 (DE3) pLysS pRSETA::xylT as well as to evade acetate accumulation, the effect of exponential feeding strategy of carbon source on the production of thermostable GI enzyme, cell concentration and acetate formation by recombinant E.coli BL21 (DE3) pLysS was investigated at four sets of fed-batch bioreactor experiments at three different predetermined specific growth rates 0.1 h-1 (M-0.1), 0.15 h-1 (M-0.15), 0.2 h-1 (M-0.2) and a glucose based exponential feeding at specific growth rate of 0.15 h-1(G-0.15) were performed by recombinant E.coli BL21 (DE3) pLysS cells. The highest biomass was obtained in M-0.15 condition as 9.6 kg m−3 at t=32 h and the highest rGI activity was achieved in M-0.1 operation as A=16399 U L-1 at t=32 h of bioprocess. Moreover, peptide ligand with specific affinity toward histidin-tag peptide was selected by phage display technology. Isothermal titration calorimetry and surface plasmon resonance analyses were carried out to determine peptide-peptide interaction properties.