Shimizu H, Kozaki Y, Kodama H, Shioya S
Department of Biotechnology, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita 565, Japan.
Biotechnol Bioeng. 1999 Mar 5;62(5):518-25.
A novel strategy for the maximum production of a biodegradable copolymer, poly(3-hydroxybutyric-co-hydroxyvaleric) acid, P(HB-co-HV), was developed, based on the kinetic parameters obtained from fed-batch culture experiments of Alcaligenes eutrophus. The effects of various culture conditions such as mole ratio of carbon:nitrogen in feed medium (C/N); total fatty acids concentrations; and addition ratio of fatty acids on cultivation properties such as the specific rates of cell formation, mu (h-1), P(HB-co-HV) production, rho[g.P(HB-co-HV)/g.cell/h], production yield from fatty acids [g.P(HB-co-HV)/g.fatty acid], and mole fraction of monomeric units in the copolymer [mol.(HV)/{mol.(HB) + mol.(HV)}], were investigated. When nitrogen supply was sufficient for cell growth; that is, C/N (mol.nitrogen atom/mol.carbon atom) was low, mu was high, but rho and the production yield were low, because fatty acids were used mainly for energy formation and anabolic reactions in the cells. On the other hand, when nitrogen supply was limited for cell growth-that is, C/N was high-rho was high. The highest value of rho was obtained when C/N was 75. As the mole ratio of valeric acid (VA) to butyric acid (BA) in the feed medium was increased, the mole fraction of HV units in P(HB-co-HV) increased linearly. When the ratio of BA to VA in the feed medium was kept at a constant value, but C/N was increased, the mole fraction of HV units decreased. In particular, when C/N was >12, the mole fraction of HV units decreased linearly as C/N increased. When VA was utilized as the sole carbon source and C/N was fixed at 4, P(HB-co-HV) with the highest mole fraction of HV units (67 mol%) was achieved. From these results, it was shown that both C/N and the mole ratio of BA to VA in the feed medium should be well controlled for an optimal production of P(HB-co-HV) with the desired value of the mole fraction of HV units. When the addition ratio of butyric acid was 50 wt% of total fatty acids, a maximum production strategy for P(HB-co-HV) was developed and realized experimentally, which was based on a model of the relationship between mu and rho.
基于从真养产碱杆菌补料分批培养实验获得的动力学参数，开发了一种用于最大量生产可生物降解共聚物聚（3-羟基丁酸-co-羟基戊酸）（P(HB-co-HV)）的新策略。研究了各种培养条件的影响，如进料培养基中碳与氮的摩尔比（C/N）、总脂肪酸浓度以及脂肪酸添加比例对培养特性的影响，这些培养特性包括细胞形成比速率（μ，h⁻¹）、P(HB-co-HV)产量（ρ，g.P(HB-co-HV)/g.cell/h）、脂肪酸的产率（g.P(HB-co-HV)/g.fatty acid）以及共聚物中单体单元的摩尔分数（mol.(HV)/{mol.(HB) + mol.(HV)}）。当氮供应足以支持细胞生长时，即C/N（mol.氮原子/mol.碳原子）较低时，μ较高，但ρ和产率较低，因为脂肪酸主要用于细胞内的能量生成和合成代谢反应。另一方面，当氮供应限制细胞生长时，即C/N较高时，ρ较高。当C/N为75时，获得了ρ的最高值。随着进料培养基中戊酸（VA）与丁酸（BA）的摩尔比增加，P(HB-co-HV)中HV单元的摩尔分数线性增加。当进料培养基中BA与VA的比例保持恒定，但C/N增加时，HV单元的摩尔分数降低。特别是当C/N>12时，HV单元的摩尔分数随着C/N的增加而线性降低。当VA用作唯一碳源且C/N固定为4时，获得了HV单元摩尔分数最高（67 mol%）的P(HB-co-HV)。从这些结果表明，为了以所需的HV单元摩尔分数最优地生产P(HB-co-HV)，进料培养基中的C/N以及BA与VA 的摩尔比都应得到很好的控制。当丁酸添加比例为总脂肪酸的50 wt%时，基于μ与ρ之间关系的模型，开发并通过实验实现了P(HB-co-HV)的最大生产策略。
