Optimization of cell growth and poly(ɛ-lysine) production in batch and fed-batch cultures by Streptomyces albulus IFO 14147

Streptomyces albulus IFO 14147 was cultivated in a stirred tank reactor; the pH and nutrient effects were evaluated in batch and fed-batch fermentation, particularly the control of pH and glucose feeding for enhancing the cell growth and ɛ-PL production were demonstrated. It was concluded that high cell growth was obtained and the cells remained stable at pH above 4.5 in the broth, while high ɛ-PL accumulation was achieved at lower pH; the high rate of cell growth at high pH was accompanied by a high rate of glucose consumption. To enhance the ɛ-PL production, a two-stage pH control and glucose feeding strategy was employed. At first sage the pH was maintained at its initial 6.8 for 48 h for achieving high cell density; the second stage aimed at increasing the ɛ-PL accumulation by maintaining pH at 4.0. In addition, pulsed feeding of glucose was carried out when it was depleted from the culture medium. By using this control and feeding strategy, the increase of ɛ-PL accumulation in 10-days cultivation is 258%. We have demonstrated that pH control and substrate feeding strategy is a feasible method for enhancing ɛ-PL production by S. albulus IFO 14147.