Abstract: A method for producing abnormal amino acids is provided, such as norleucine and norvaline, using a bacterium of Enterobacteriaceae family, particularly a bacterium belonging the genus Escherichia which has all acetohydroxy acid synthases (AHASes) inactivated.

Abstract: A process for producing an L-amino acid, such as L-isoleucine, L-histidine, L-threonine and L-tryptophan, using bacterium belonging to the genus Escherichia is provided which comprises cultivating the L-amino acid-producing bacterium in a culture medium and collecting the L-amino acid from the culture medium, wherein the culture medium contains a mixture of glucose and pentose sugars, such as arabinose and xylose, as the main carbon source.