Two-stage pH Control Strategy Research Articles

Combined dissolved oxygen and pH control strategy to improve the fermentative production of l-isoleucine by Brevibacterium lactofermentum

The effect of both dissolved oxygen (DO) and pH on L: -isoleucine production by batch culture of Brevibacterium lactofermentum was investigated. A two-stage agitation speed control strategy was developed, and the isoleucine production reached 23.3 g L(-1) in a relative short time (52 h), increased by 11.6% compared to the results obtained in the single agitation speed control process. In order to make sure whether the combination of DO and pH control can boost the production by a mutual effect, different control modes were conducted, based on the data obtained from the two-stage agitation speed control strategy and the analysis of kinetics parameters at different pH values. The results showed that the mode of combining two-stage DO with two-stage pH control strategy was the optimal for isoleucine production. The isoleucine production can reach 26.6 g L(-1) at 56 h, increased by 14.3% comparing to that obtained by the single two-stage DO control strategy.

PH control strategy in a shaken minibioreactor for polysaccharide production by medicinal mushroom Phellinus linteus and its anti-hyperlipemia activity

A process at various pH values ranging from 4.5 to 7.5 for production of mycelia and extracellular polysaccharide (EPS) by P. linteus fermentation in pH-controlled shaken bioreactor was investigated. A two-stage pH control strategy in which pH value was kept at 6.5 for the first 24 h, and then switched to 4.5 was developed successfully to enhance simultaneously the cell growth and EPS production. The maximum cell density and EPS production reached 15.13 +/- 0.1 g/l on day 6 and 6.74 +/- 0.1 g/l on day 4, respectively. The anti- hyperlipemia effect of EPS and intracellular polysaccharide (IPS) extracted from mycelia were observed that both EPS and IPS can obviously reduce the serum triglyceride (TG), the blood cholesterol (TC) and serum low density lipoprotein (LDL) level, and increase the high density lipoprotein (HDL) level of the hyperlipemia mice. Polysaccharides from submerged cultivation of medicinal fungus P. linteus have favorable potency to develop anti-hyperlipermia drugs.

Enhanced cutinase production with Thermobifida fusca by two‐stage pH control strategy

A mutant of Thermobifida fusca ATCC 27730 was used for cutinase production. Acetate was the most suitable carbon source for cell growth and cutinase production compared with others. The pH was one of the most important factors affecting cutinase yield and productivity. Batch cutinase fermentations by mutant Thermobifida fusca WSH04 at various pH values ranging from 7.0 to 7.9 were studied. Based on the effects of different pH values on the specific cell growth rate and specific cutinase formation rate, a two-stage pH control strategy was developed, in which the pH was set at 7.3 for the first 20 h, and switched to 7.6 afterwards. By applying this two-stage pH control strategy for cutinase fermentation, the maximal cutinase activity reached 19.8 U/mL.

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.

Improvement of exopolysaccharide production by macro-fungus Auricularia auricula in submerged culture

The effect of culture conditions and pH on the performance of exopolysaccharide (EPS) production by Auricularia auricula, an edible and medical macro-fungus, was investigated in submerged culture. First, the optimal cultivation condition was determined in shake flasks by the single-factor tests. Second, the effect of pH on EPS production was investigated in batch submerged fermentation, a highest EPS concentration (7.5 ± 0.14 g/l), a highest mycelial growth rate but a lowest residual glucose concentration (3.9 ± 0.04 g/l) were achieved at the pH 5.5, 5.0 and 4.5, respectively. Based on kinetic parameters analysis, a two-stage pH-control strategy was proposed, in which pH was controlled at 5.0 in the first 48 h and then switched to 5.5. The effectiveness of the strategy was verified successfully by experiments. Higher concentration (8.7 ± 0.08 g/l) and productivity (0.091 g/l/h) of EPS were achieved by applying this strategy. The productivity increased 93.3, 110.4 and 45%, respectively, compared with that of the non-pH control, and controlling pH at 5.0 and 5.5. Those results demonstrated that EPS production by A. auricula was sensitive to the pH change in submerged culture. In addition, the idea of changing environmental conditions at different culture stages to suit the metabolic characteristics of cell, could be applied to the other bioactive metabolites production from macro-fungi in submerged culture.

Culture pH Affects Exopolysaccharide Production in Submerged Mycelial Culture of Ganoderma lucidum

In submerged culture of Ganoderma lucidum, the pH optimum for cell growth has been shown to be lower than that for exopolysaccharides (EPS) formation. Therefore, in the present study, a two-stage pH-control strategy was employed to maximize the productions of mycelial biomass and EPS. When compared, a batch culture without pH control had a maximum concentration of EPS and endopolysaccharides, which was much lower than those with pH control. Maximum mycelial growth (12.5 g/L) and EPS production (4.7 g/L) were achieved by shifting the controlled pH from 3.0 to 6.0 after day 4. The contrast between the controlled-pH process and uncontrolled pH was marked. By using various two-stage culture processes, it was also observed that culture pH has a significant affect on the yield of product, mycelial morphology, chemical composition, and molecular weight of EPS. A detailed observation of mycelial morphology revealed that the productive morphological form for EPS production was a dispersed pellet (controlled pH shifting from 3.0 to 6.0) rather than a compact pellet with a dense core area (controlled pH 4.5) or a feather-like pellet (controlled pH shifting from 6.0 to 3.0). Three different polysaccharides were obtained from each pH conditions, and their molecular weights and chemical compositions were significantly different.