The present invention provides a microorganism which comprises a chromosomal DNA lacking a part or entire of the gene encoding a protein having the amino acid sequence as shown in SEQ ID NO: 1 or 2, or the gene encoding a protein having 80% or more homology with the amino acid sequence as shown in SEQ ID NO: 1 or 2, and has the ability to produce a useful substance; a process for producing a useful substance using said strain; especially a process for producing a useful substance which is selected from the group consisting of proteins, peptides, amino acids, nucleic acids, vitamins, saccharides, organic acids, and lipids.