Plant cells contain a wide range of interesting secondary metabolites, which are used as natural pigments and flavoring agents in foods and cosmetics as well as phyto‐pharmaceutical products. However, conventional industrial extraction from whole plants or parts of them is limited due to environmental and geographical issues. The production of secondary metabolites from in vitro cultures can be considered as alternative to classical technologies and allows a year‐round cultivation in the bioreactor under optimal conditions with constant high‐level quality and quantity. Compared to plant cell suspensions, differentiated plant in vitro systems offer the advantage that they are genetically stable. Moreover, the separation of the biomass from culture medium after fermentation is much easier. Nevertheless, several investigations in the literature described that differentiated plant in vitro systems are instable concerning the yield of the target metabolites, especially in submerged cultivations. Other major problems are associated with the challenges of cultivation conditions and bioreactor design as well as upscaling of the process. This article reviews bioreactor designs for cultivation of differentiated plant in vitro systems, secondary metabolite production in different bioreactor systems as well as aspects of process control, management, and modeling and gives perspectives for future cultivation methods.

Optimizing illumination is essential for optimizing the growth of phototrophic cells and their production of desired metabolites and/or biomass. This requires appropriate modulation of light and other key inputs and continuous online monitoring of their metabolic activities. Powerful noninvasive systems for cultivating heterotrophic organisms include shake flasks in online monitoring units, but they are rarely used for phototrophs because they lack the appropriate illumination design and necessary illuminatory power. This study presents the design and characterization of a photosynthetic shake flask unit, illuminated from below by warm white light‐emitting diodes with variable light intensities up to 2300 μmol m−2 s−1. The photosynthetic unit was successfully used, in combination with online monitoring of oxygen production, to cultivate Arthrospira platensis. In phototrophic growth under continuous light and a 16 h light/8 h dark cycle (light intensity: 180 μmol m−2 s−1), the oxygen transfer rate and biomass‐related oxygen production were −1.5 mmol L−1 h−1 and 0.18 mmol O2 gx−1 h−1, respectively. The maximum specific growth rate was 0.058 h−1, during the exponential growth phase, after which the biomass concentration reached 0.75 g L−1.

An agent-based model for simulating the in vitro growth of Beta vulgaris hairy root cultures is described. The model fitting is based on experimental results and can be used as a virtual experimentator for root networks. It is implemented in the JAVA language and is designed to be easily modified to describe the growth of diverse biological root networks. The basic principles of the model are outlined, with descriptions of all of the relevant algorithms using the ODD protocol, and a case study is presented in which it is used to simulate the development of hairy root cultures of beetroot (Beta vulgaris) in a Petri dish. The model can predict various properties of the developing network, including the total root length, branching point distribution, segment distribution and secondary metabolite accumulation. It thus provides valuable information that can be used when optimizing cultivation parameters (e.g., medium composition) and the cultivation environment (e.g., the cultivation temperature) as well as how constructional parameters change the morphology of the root network. An image recognition solution was used to acquire experimental data that were used when fitting the model and to evaluate the agreement between the simulated results and practical experiments. Overall, the case study simulation closely reproduced experimental results for the cultures grown under equivalent conditions to those assumed in the simulation. A 3D-visualization solution was created to display the simulated results relating to the state of the root network and its environment (e.g., oxygen and nutrient levels).

This study focuses on the morphological development and secondary metabolite production of the red pigments from the group of betacyanins in hairy roots of Beta vulgaris. We demonstrate a working, medium throughput, customized, automatic image recognition solution for hairy roots on agar plates including the evaluation of 12 experimental samples. Image acquisition is conducted under comparable para‐meters using a tripod with light emitting diode background lighting and a digital single lens reflex camera. The server‐based image recognition system developed together with Wimasis GmbH, Munich, Germany helps to obtain not only quantitative values for morphological parameters, such as segment lengths and widths or metabolite concentrations, but also global parameters of root growth, such as total root length or the number of branching points. Using timed diagrams the development of the total root length, the total number of branching points, and the mean pigment concentration during the cultivation period were determined. The generated data present the basis for detailed mathematical modeling in order to achieve a structured growth model for hairy roots. A mathematical model for growth of hairy roots can be used to decrease experimental efforts as well as to optimize cultivation conditions and the bioreactor design.

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