Efficient production of menaquinone (vitamin K-2) by a menadione-resistantmutant of Bacillus subtilis

Efficient production of menaquinone (MK) by Bacillus subtilis was achieved. An edible strain of B. subtilis, isolated from the traditional Japanese fo od natto, was mutated to improve MK productivity. A menadione-resistant mut ant producing 30% more MK than its parent strain was obtained, Soybean extr act and glycerol were the best nitrogen and carbon sources, respectively, a mong the sources tested. Addition of yeast extract also increased MK produc tivity. The maximum concentration of MK reached about 35.0 mg/l after 4 day s of culture in a jar fermenter. The pH of the medium decreased to 5.5 afte r the start of cultivation, then spontaneously increased to 7.7-8.0. This p H change might be important in the production of MK because only small amou nts of MK were obtained when pH was controlled at 5.7, 6.0, 7.0, 7.5 or 8.0 .