Influence of load-induced morphological changes on the productivity of the filamentous pellet system Actinomadura namibiensis

丝状微生物是生产药物化合物、抗生素、蛋白质和有机酸的许多工业生物技术过程的核心。这些微生物通常在搅拌槽或摇瓶中培养成分散的菌丝体或颗粒。颗粒微生物的一个特征是颗粒形态与颗粒生长和生产力之间的紧密联系。特别是，细丝在颗粒内的分布控制着内部质量传输，这反过来又影响颗粒核心中细丝的生存能力，并决定潜在的底物限制。虽然颗粒的形态对颗粒的活性和生产率至关重要，但过去的实验研究表明，颗粒的形态主要由培养条件和颗粒所经历的机械载荷决定。在单个球团的水平上，机械载荷、形貌和生产率之间的强烈相互作用构成了我们研究项目的核心。根据施加在颗粒上的机械力、形态变化率和颗粒新陈代谢的动力学表达式，我们的目标是概念化和开发一个前所未有的逼真度的物理模型，用于分析和预测颗粒深层培养中的产品产量。从长远来看，这种新的模型可以用来推断反应器设计、搅拌和操作的指导方针，目标是实现能耗、培养时间和产品产量的最佳。这与现有的模型形成鲜明对比，现有模型仅限于特定的反应器结构和操作条件，并且忽略了负载引起的分散颗粒的形态变化。在所提出的模型范围内，我们结合了对完美搅拌反应器中颗粒种群的长期描述与在很短的时间尺度上流动分辨确定颗粒特定负荷集合，从而在特征混合和培养时间之间的广泛尺度之间架起了桥梁。原核生物南美放线菌作为丝状模式生物，适合在摇瓶中进行实验室规模的培养，并产生多肽抗生素迷宫肽A1。为了校准和验证所提出的模型，我们计划了一个双轨实验活动。一方面，记录了摇瓶中底物和产物浓度的时间变化以及颗粒群中的形态分布。另一方面，进行了针对颗粒的透气性、内部氧分布和机械刚度的分析实验。

Filamentous microorganisms are central to many industrial biotechnological processes for the production of pharmaceutical compounds, antibiotics, proteins and organic acids. These microorganisms are commonly cultivated in stirred tanks or shaking flasks either as dispersed mycelia or pellets. A characteristic property of pelleted microorganisms is the tight connection between the pellet morphology and the pellet growth and productivity. In particular, the distribution of filaments within a pellet controls the internal mass transport which, in turn, affects the viability of filaments in the pellet core and determines potentional substrate limitations. While the morphology is vital for the viability and productivity of the pellets, past experimental investigations have shown that the morphology is predominantly shaped by the cultivation conditions and the mechanical loads experienced by the pellets. The strong interactions between mechanical loads, morphology and productivity on the level of a single pellet constitute the core of our research project. Based on kinetic expressions for the mechanical forces exerted on a pellet, the rate of change of morphology and the pellet metabolism, our objective is to conceptualise and develop a physical model of unprecedented fidelity for the analysis and prediction of the product yield in pelleted, submerged cultures. Perspectively, the novel model may be deployed to infer guidelines on reactor design, agitation and operation, targeting an optimum of power consumption, cultivation duration and product yield. This is in sharp contrast to existing models which are restricted to particular reactor configurations and operating conditions and in which load-induced morphological changes of the dispersed pellets are neglected. Within the scope of the proposed model, we combine a long-time description of pellet populations in a perfectly stirred reactor with the flow-resolved determination of pellet-specific load collectives on very short time scales, thus bridging the wide range of scales between characteristic mixing and cultivation times. The procaryot Actinomadura namibiensis serves as filamentous model organism as it is amenable to lab-scale cultivation in shaking flasks and produces the peptid antibiotic Labyrinthopeptin A1. In order to calibrate and validate the proposed model, we plan a two-track experimental campaign. On the one hand, the temporal changes of the substrate and product concentrations in the shaking flask are recorded along with the morphology distribution across the pellet population. On the other hand, pellet-specific experiments for the analysis of permeability, internal oxygen distribution and mechanical stiffness are undertaken.