Review: 217 refs.

No abstract

Biochemistry Z 0250 Monoliths as Biocatalytic Reactors: Smart Gas-Liquid Contacting for Process Intensification -[31 refs.]. -(KREUTZER, M. T.; KAPTEIJN, F.; MOULIJN, J. A.; EBRAHIMI, S.; KLEEREBEZEM, R.; VAN LOOSDRECHT, M. C. M.; Ind. Eng. Chem. Res. 44 (2005) 25, 9646-9652; React. Catal. Eng. Group, Delft Univ. Technol., NL-2628 BL Delft, Neth.; Eng.) -Lindner 02-276

Improvement of the microorganism's product yield on feedstock is possible by targeted genetic modification, which requires a solid understanding of the species metabolism and genetics. Alternatively, genetic modifications can be introduced randomly such that the chance that a resulting mutant performs better than the original one is small. Consequently, many mutants need to be created and subsequently screened in order to identify the best performing ones. [1] Given the large number of experiments, it is common practice to grow and study all the different mutants in individual microliter-sized wells on microtiter plates. While this allows for parallel screening in an automated fashion using pipetting robots and plate readers, conventional microtiter plates lack the ability to feed nutrients and control pH by base or acid addition. It is indeed challenging to feed liquids at flow rates in the nanoliter per hour range to all the individual wells of a microtiter plate and to do so accurately. Therefore, screening of mutants is commonly performed under batch conditions with all feedstock present from the start and no further control over feedstock concentration and pH. In contrast, more than 80% of the processes in industrial biotechnology are operated under so called fed-batch conditions with control over feedstock concentration and pH. [2,3] This incompatibility between the physiological conditions during screening and industrial operation not only leads to selection of false positives which fail to generate competitive yields at industrial scale, but also fails to identify the best mutants for fed-batch conditions. [4][5][6] The effectiveness of screening hence greatly benefits from a technology that enables growing and studying a large number of microorganisms under precisely controlled conditions representative of industrial bioreactors. Besides screening of mutants, optimization of process conditions, a second important aspect in bioprocess development, also benefits from such a technology. [7] Although there has been progress in recent years, there remains both need and opportunity to cost-effectively and with fidelity miniaturize fermentation to screen under fed-batch conditions.Several strategies have been developed to study microorganisms under controlled growth conditions. One strategy is to A key bottleneck in bioprocess development is that state-of-the-art tools used for screening of cells and optimization of cultivation conditions do not represent the conditions enforced at industrial scale. At industrial scale, cell growth is strictly controlled ("fed-batch") to optimize the metabolites produced by the cells. In contrast, cell growth is uncontrolled ("batch") in microwells commonly used for bioprocess development due to the difficulty to continuously supply minute amounts of nutrients to the cells in these wells over the course of the cultivation experiment. This work addresses this bottleneck through the development of a droplet-based fed-batch nanobioreactor.A key challenge addressed in this work is ...

It is common practice in the development of bioprocesses to genetically modify a microorganism and study a large number of resulting mutants in order to select the ones that perform best for use at the industrial scale. At industrial scale, strict nutrient-controlled growth conditions are imposed to control the metabolic activity and growth rate of the microorganism, thereby enhancing the expression of the product of interest. Although it is known that microorganisms that perform best under these strictly controlled conditions are not the same as the ones that perform best under uncontrolled batch conditions, screening, and selection is predominantly performed under batch conditions. Tools that afford high throughput on the one hand and dynamic control over cultivation conditions on the other hand are not yet available. Microbioreactors offer the potential to address this problem, resolving the gap between bioprocess development and industrial scale use. In this review, we highlight the current state-of-the-art of microbioreactors that offer the potential to screen microorganisms under dynamically controlled conditions. We classify them into: (i) microtiter plate-based platforms, (ii) microfluidic chamber-based platforms, and (iii) microfluidic droplet-based platforms. We conclude this review by discussing the opportunities of nutrient-fed microbioreactors in the field of biotechnology.