Enhancement of epsilon-polylysine production by Streptomyces albulus strain 410 using pH control.

The enhancement of epsilon-poly-l-lysine (epsilon-PL) production by Streptomyces albulus strain no. 410 (S410) by means of a pH control strategy was investigated. S140 cells produce epsilon-PL at a high concentration if the culture pH remains at about 4.0; however, if it shifts to higher than 4.0, the accumulated epsilon-PL is depolymerized. We therefore suggest a pH control strategy for cell growth and epsilon-PL production aimed at increasing the amount of epsilon-PL produced. The cultivation was divided into two control phases. In phase I, cell growth was accelerated by maintaining the pH at higher than 5.0; in phase II, epsilon-PL production was increased by maintaining the pH at about 4.0. To avoid an increase in the pH during phase II as a result of glucose depletion, the glucose concentration was kept at around 10 g/l by glucose feeding. This control strategy enhanced the production of epsilon-PL to 48.3 g/l from 5.7 g/l in the case of batch culture.

Optimization of tylosin feeding rate profile in production of acetyl-isovaleryl tylosin (AIV) from tylosin by Streptomyces thermotolerans YN554.

An optimal feed rate profile of a substrate (tylosin) for a novel antibiotic, acetyl-isovaleryl tylosin (AIV) production process was investigated. In the first step of optimization, a kinetic model for production of AIV from tylosin by Streptomyces thermotolerans was established properly using the least square method, followed by the confirmation that the proposed model could be used to predict the production process of AIV from tylosin. An objective function, state equations and an inequality constraint with respect to the tylosin feeding rate profile were applied to maximize the amount of AIV produced from tylosin in a fed-batch culture. The optimized tylosin feeding rate profile was determined using a direct iterative search algorithm based on the modified complex method. The simulation of AIV production at the optimal tylosin feeding profile indicates that the final amount of AIV is expected to be about 30% higher than that at the conventional constant tylosin feeding rate, which was also confirmed experimentally using a 30-l jar fermentor.

Kinetics of soybean oil consumption and cephamycin C production in culture of Streptomyces sp. using mineral support.

A simple kinetics of soybean oil consumption and cephamycin C production in Streptomyces sp. culture using a mineral support is proposed in this study. The mineral support was used for both suspending the soybean oil as fine oil droplets and immobilizing mycelia. The optimum concentrations of oil and mineral support for obtaining the maximum cephamycin C production were determined to be 50 and 15 g/l, respectively, by the proposed kinetics. At the optimal concentrations, the concentration of cephamycin C estimated from the proposed model and from the experimental data was 2.82 and 2.80 g/l, respectively. The results of the simulation coincided well with the experimental data for various concentrations of the soybean oil and the support. This demonstrates that our model can explain the kinetics of a culture using vegetable oil as the carbon source and mineral support for both oil suspension and mycelial immobilization.

Effect of soybean oil on oxygen transfer in the production of tetracycline with an airlift bioreactor.

Corn starch and soybean oil are suitable carbon sources for the production of tetracycline by Streptomyces aureofacience CG-1. However, it could not produce more than 6 g/l of tetracycline even if initial corn starch concentration was increased to more than 100 g/l. It was confirmed by shaking flask experiments that the k(L)a in a mixture of 2% soybean oil in water was four folds compared with that without soybean oil. With the addition of soybean oil to the starch medium in a shaking flask, tetracycline production was significantly improved. By scaling-up to a 5.5-l airlift bioreactor from 500-ml Erlenmeyer flask, more than 10 g/l of tetracycline was produced with the addition of 60 g/l of soybean oil to the medium containing 100 g/l of corn starch. The dissolved oxygen level in the airlift bioreactor containing soybean oil was higher than that without soybean oil. This suggests that soybean oil is not only a suitable carbon source but is also a surface-active agent which may accelerate the oxygen transfer. This may lead to the possibility of the enhanced production of tetracycline at a low cost in airlift bioreactor.