The natural ability of Pseudomonas taiwanensis VLB120 to use xylose as sole carbon and energy source offers a high potential for sustainable industrial biotechnology. In general, three xylose assimilation routes are reported for bacteria. To elaborate the metabolic capacity of P. taiwanensis VLB120 and to identify potential targets for metabolic engineering, an in silico/in vivo experiment was designed, allowing for discrimination between these pathways. Kinetics of glucose and xylose degradation in P. taiwanensis VLB120 was determined and the underlying stoichiometry was investigated by genome-based metabolic modelling and tracer studies using stable isotope labelling. Additionally, reverse transcription quantitative polymerase chain reaction experiments have been performed to link physiology to the genomic inventory. Based on in silico experiments, a labelling strategy was developed, ensuring a measurable and unique (13) C-labelling distribution in proteinogenic amino acids for every possible distribution between the different xylose metabolization routes. A comparison with in vivo results allows the conclusion that xylose is metabolized by P. taiwanensis VLB120 via the Weimberg pathway. Transcriptomic and physiological studies point to the biotransformation of xylose to xylonate by glucose dehydrogenase. The kinetics of this enzyme is also responsible for the preference of glucose as carbon source by cells growing in the presence of glucose and xylose.
Recent environmental economic developments generate a need for sustainable and cost‐effective (microbial) processes for the production of high‐volume, low‐priced bulk chemicals. As an example, n‐butanol has, as a second‐generation biofuel, beneficial characteristics compared to ethanol in liquid transportation fuel applications. The industrial revival of the classic n‐butanol (ABE) fermentation requires process and strain engineering solutions for overcoming the main process limitations: product toxicity and low space–time yield. Reaction intensification on the biocatalyst, fermentation, and bioprocess level can be based on economic and ecologic evaluations using quantifiable constraints. This review describes the means of process intensification for biotechnological processes. A quantitative approach is then used for the comparison of the massive literature on n‐butanol fermentation. A comprehensive literature study—including key fermentation performance parameters—is presented and the results are visualized using the window of operation methodology. The comparison allowed the identification of the key constraints, high cell densities, high strain stability, high specific production rate, cheap in situ product removal, high n‐butanol tolerance, to operate in situ product removal efficiently, and cheap carbon source. It can thus be used as a guideline for the bioengineer during the combined biocatalyst, fermentation, and bioprocess development and intensification.
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