Metabolism of galactose in Zymomonas mobilis

Zymomonas mobilis IFO 13 756 could take up galactose and metabolize it so that galactonic acid accumulated in the culture fluid. The oxidation of galactose was catalysed by a membrane-associated enzyme, which could be solubilized with a mixture of 1% Triton X-100 and 1 M: KC1. The strain also accumulated galactitol as a minor metabolite. To confer the ability to utilize galactose on Z. mobilis, a Gal(+) recombinant plasmid, pZG13, was constructed by the insertion of the galETK genes of Escherichia coli immediately downstream of the Z. mobilis promoter gene in pZA22, the plasmid introduced into a Zymomonas strain. Uridine diphospho-glucose 4-epimerase coded in the galE gene was expressed in Z. mobilis carrying pTG13. The recombinant strain could produce a small amount of ethanol from galactose.