Abstract: The present invention relates to a recombinant strain having a modified sugar metabolic pathway resulting from the introduction of an enzyme derived from a different strain to a strain, and a high-speed screening method for various mutants and variants by which useful materials can be obtained or which can produce useful materials. The use of a recombinant vector and a strain according to the present invention not only can construct a new metabolic pathway in a strain to effectively obtain D-tagatose from D-galactose, but also can introduce randomly modified sugar isomerases and then allow D-galactose isomerase variants to be rapidly screened by conducting a cell growth-associated screening system.