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In addition, zinc plays a role in the regulation of growth and citric acid accumulation. High zinc maintains citric acid's growth phase (when the cells proliferate but do not accumulate citrate), while at low zinc the cultures pass into accumulating phase (when they produce citrate but do not proliferate). Addition of zinc to accumulating cultures results in their reversion to growth phase. Iron, manganese, calcium at high concentrations had no influence on either growth or citrate accumulation.