Mutant of Escherichia coli with derepressed levels of the biotin biosynthetic enzymes.

A cross-feeding technique was used to isolate a mutant of Escherichia coli K-12 that excretes 1,000 times more biotin into the growth medium than the parent strain. The mutant has high levels of the biotin biosynthetic enzymes even when grown in the presence of biotin. Desthiobiotin synthetase, the level of which was used as a measure of the biosynthetic activity of the biotin pathway, is not repressed by biotin at the concentration 250,000 times that sufficient to repress the enzyme in the wild type. The mutant gene is cotransducible with argC located at 77 min on the E. coli chromosome.