Growth kinetics and nitrogenase induction inFrankia sp. HFPArI 3 grown in batch culture

Summary Kinetics of growth and nitrogenase induction inFrankia sp. Ar13 were studied in batch culture. Growth on defined medium with NH ₄ ⁺ as the N source displayed typical batch culture kinetics; however, a short stationary phase was followed by autolysis. Removal of NH ₄ ⁺ arrested growth and initiated vesicle differentiation. Vesicle numbers increased linearly and were paralleled by a rise in nitrogenase (acetylene reduction) activity. Nitrogenase activity (10 nM C₂H₄·mg protein^–1·min^–1) was sufficient to support growth on N₂ and protein levels rose in parallel with nitrogenase induction. Optimal conditions for vesicle and nitrogenase induction were investigated. Maximum rates of acetylene reduction were obtained with 5 to 10 mM K₂ HPO₄/KH₂PO₄, 0.1 mM CaCl₂ and MgSO₄. The optimum pH for acetylene reduction and respiration was around 6.7. The amount (5 to 10 g protein/ml) and stage (exponential) of growth of the ammonium-grown inoculum strongly influenced the subsequent development of nitrogenase activity. Propionate was the most effective carbon source tested for nitrogenase induction. Respiration in propionate-grown cells was stimulated by CO₂ and biotin, suggesting that propionate is metabolized via the propionyl CoA pathway.