Bacillus subtilis ATCC 21332 produces an extracellular lipopeptide, called surfactin, a potent surfactant. Using a new technique for cell culturing, continuous phasing with feedback control, the effects of manganese on the growth, and the associated production of surfactin, were investigated. An intimate relationship was revealed between the availability of iron and manganese and the utilization of nitrogen. A critical proportionality of 920/7.7/1.0 (molar basis) of nitrogen to iron to manganese was identified. Increasing the manganese reduced the requirement for nitrogen and resulted in growth under iron limitation. The production of surfactin could be sustained for at least 30 consecutive generations growing under either an iron or nitrogen limitation, but only if manganese was available. The dynamic response of B. subtilis to changes in manganese concentration revealed a non-linear relationship that required several generations to stabilize.