US Patent 7494801 Method of selecting

The invention relates to a selection method of an Escherichia coli mutant strain which expresses an exogenous gene at a high level, wherein stress resistance such as hydrogen peroxide decomposition activity is used as an index, the Escherichia coli mutant strain selected thereby and production methods of enzyme using the strain and of useful compounds like amino acids (especially L-amino acid) and the like using the strain. According to the selection method of the invention, an Escherichia coli mutant strain where gene expression amount does not decrease with passage can be obtained, and a compound using a plant-derived ammonia lyase can be efficiently produced.