Calcium chloride improve ethanol production in recombinant Zymomonas mobilis
The T7-expression system has been very useful for protein expression in Escherichia coli. Here, a T7- expression transposon was constructed, which allowed simple construction of T7-expression Zymomonas mobilis. This transposon contained the T7 RNA polymerase being driven by the gap promoter from Z. mobilis. The T7-expression fadK genomes were introduced into Z. mobilis ATCC 31821 in order to increase ethanol production. The recombinant bacteria were named as Z.M.F-1, Z.M.F-2, Z.M.F-3, and Z.M.F-4. However, Z.M.F-4 had the highest ability of producing ethanol by selection. Compared with Z. mobilis ATCC 3182, there was 7% increase in ethanol production for Z.M.F-4 with corn hydrolyaztes as fermentation medium. The 16 mmolL-1 supplement of calcium chloride could significantly improve the ethanol production. This was also clearly demonstrated by a variety of kinetic parameter values over time in Z.M.F-4 under high sugar osmotic stress. Calcium chloride not only increased the fermentation ability but also improved the stability of cell membrane.
Key words: Calcium chloride, fadK, fermentation, Zymomonas mobilis.