This study examined how nutrient availability affects extracellular product formation in Bacillus licheniformis. Researchers grew cultures in defined media where either glucose or ammonium was the growth-limiting nutrient, while varying concentrations of excess magnesium. They measured serine protease and bacitracin production during stationary phase. Results showed that the growth-limiting nutrient profoundly influenced both protease and bacitracin levels, with four-fold higher protease production when ammonium (rather than glucose) limited growth. Excess nutrient concentrations also affected production, with ammonium and glucose repressing both products at high levels, though bacitracin was unaffected by glucose excess in nitrogen-exhausted cultures. Magnesium below 0.25 mM reduced protease production but had minimal effects on bacitracin. Importantly, protease and bacitracin responded differently to these conditions, indicating separate regulatory mechanisms. The work demonstrates the critical importance of precisely defined culture conditions for studying relationships between sporulation and secondary metabolite production.

Key findings

• Protease production increased four-fold when ammonium (rather than glucose) was the growth-limiting nutrient, reflecting an energy requirement for protease synthesis.
• Bacitracin and serine protease are subject to independent control mechanisms, as they respond differently to varying nutrient conditions despite their concurrent production.
• High concentrations of excess ammonium chloride and glucose repressed protease synthesis, but glucose excess did not repress bacitracin production.
• Magnesium availability below 0.25 mM reduced protease production in both glucose- and nitrogen-limited cultures but minimally affected bacitracin production.
• Rigorously controlled, nutrient-defined media are essential for studying secondary metabolite production to distinguish effects of growth rate changes from direct effects of specific chemical nutrients.