The Effects of Metal Ions on Diacetyl Production by Streptococcus lactis subsp. diacetylactis3022

Abstract

Streptococcus lactis subsp. diacetylactis 3022 produced 5.4 times the amount of diacetyl on 24 hours incubation in 30% RSM medium supplemented with 1 mm Cu^{2 +}, compared to that in the medium without Cu^{2 +}. However, the citrate utilization in the medium with Cu²⁺ was considerably repressed. On the other hand, the diacetyl formation activity of the cells was markedly stimulated by adding Cu^{2 +}, Fe^{2 +}, Fe^{3 +}, Co²⁺ and Mo⁶⁺ to the reaction mixture. Cu²⁺ and Co²⁺ also stimulated citrate lyase. Cu²⁺ was the most effective stimulator for these activities. These metal ions had no effects on citrate uptake activity or diacetyl reductase activity.

After the addition of MRS medium with and without Cu²⁺ to a culture incubated at 30°C for 24 hours, the cells in the medium with Cu^{2 +} produced.a larger amount of diacetyl than those in the medium without Cu^{2 +}. On the contrary, the citrate utilization of the former cells was inferior to that of the latter. From these results, it appeared that diacetyl reductase activity was lowered by citrate remaining in the medium with Cu^{2 +} and that the metal ion in the medium stimulated the activities of diacetyl formation and citrate lyase.