Genetic engineering of Bacillus subtilis for the commercial production of riboflavin

Recombinant DNA engineering was combined with mutant selection and fermenta tion improvement to develop a strain of Bacillus subtilis that produces com mercially attractive levels of riboflavin, The B. subtilis riboflavin produ ction strain contains multiple copies of a modified B. subtilis riboflavin biosynthetic operon (rib operon) integrated at two different sites in the B . subtilis chromosome. The modified rib operons are expressed constitutivel y from strong phage promoters located at the 5' end and in an internal regi on of the operon, The engineered strain also contains purine analog-resista nt mutations designed to deregulate the purine pathway (GTP is the precurso r for riboflavin), and a riboflavin analog-resistant mutation in ribC that deregulates the riboflavin biosynthetic pathway.