Institute of Microbial Technology, Sector 39-A, Chandigarh-160036, India.
J Biol Eng. 2008 Mar 27;2:4. doi: 10.1186/1754-1611-2-4.
Although the production of poly-beta-hydroxybutyrate (PHB) has many biological, energetic and environmental advantages over chemically synthesized polymers, synthetic polymers continue to be produced industrially since the productivities of fermentation processes fr PHB are not yet economically competitive. Improvement of a PHB fermentation requires good understanding and optimization under the realistic conditions of large bioreactors.Laboratory-scale studies have shown that co-cultures of Ralstonia eutropha and Lactobacillus delbrueckii generate better fermentation efficiencies than R. eutropha alone. In large bioreactors, incomplete dispersioin and perturbations in the dissolved oxygen (DO) concentration, both of which affect the fermentation, have to be considered. This study analyzes the effect of DO fluctuations on bioreactor performance for both ideal and optimally dispersed broths.
Response coefficient analysis was employed to obtain quantitative information on the effect of DO perturbations on different variables. Three values of the Peclet number (Pe) cheracterized three levels of dispersion: Pe = 0.01 for nearly complete dispersion, Pe = 20 for optimum dispersion and Pe = 60 for insufficient dispersion. The response coefficients (RCs) of the pairs of bacterial concentrations and the main substrates, glucose and ammonium chloride, showed contrasting variations with time. Lactate, a critical intermediate, and PHB had similar RC profiles but those of lactate were one to two orders of magnitude larger than other RCs. Significantly, the optimum Pe also resulted in the largest RCs, suggesting a balance between productivity and reactor stability.
Since R. eutropha requires oxygen for its growth whereas L. delbrueckii does not, fluctuations in the DO concentartion have a strong influence on the fermentation. Apart from this, the mechanism of PHB biosynthesis indicates that control of lactate is a critical determinant of fermentation efficiency. The RC profiles indicate that, under non-ideal conditions, a compromise may be required between PHB formation and reactor stability, especially in the latter half of the process.
尽管聚-β-羟基丁酸酯（PHB）的生产在生物学、能量学和环境方面优于化学合成聚合物，但由于 PHB 发酵工艺的生产力在经济上还没有竞争力，因此合成聚合物仍在工业上生产。改善 PHB 发酵需要在大生物反应器的实际条件下进行良好的理解和优化。实验室规模的研究表明，与单独的 Ralstonia eutropha 相比，Ralstonia eutropha 和 Lactobacillus delbrueckii 的共培养可以产生更好的发酵效率。在大生物反应器中，必须考虑不完全分散和溶解氧（DO）浓度波动这两个影响发酵的因素。本研究分析了 DO 波动对理想和最佳分散培养基的生物反应器性能的影响。
采用响应系数分析方法获得了 DO 扰动对不同变量影响的定量信息。 Peclet 数（Pe）的三个值表征了三种分散水平：Pe = 0.01 表示几乎完全分散，Pe = 20 表示最佳分散，Pe = 60 表示分散不足。细菌浓度和主要基质（葡萄糖和氯化铵）对的响应系数（RC）随时间表现出相反的变化。乳酸是一种关键的中间产物，与 PHB 具有相似的 RC 谱，但乳酸的 RC 谱比其他 RC 大一个或两个数量级。重要的是，最佳 Pe 也导致了最大的 RC，表明在生产力和反应器稳定性之间存在平衡。
由于 R. eutropha 的生长需要氧气，而 L. delbrueckii 不需要，因此 DO 浓度的波动对发酵有很大的影响。除此之外，PHB 生物合成的机制表明，控制乳酸是发酵效率的关键决定因素。RC 谱表明，在非理想条件下，特别是在发酵过程的后半段，可能需要在 PHB 形成和反应器稳定性之间做出妥协。
