W.-D. Deckwer

Bio: W.-D. Deckwer is an academic researcher from Braunschweig University of Technology. The author has contributed to research in topics: Glycerol & Fermentation. The author has an hindex of 23, co-authored 33 publications receiving 2927 citations.

Microbial production of 1,3-propanediol.

Abstract: 1,3-Propanediol (1,3-PD) production by fermentation of glycerol was described in 1881 but little attention was paid to this microbial route for over a century. Glycerol conversion to 1,3-PD can be carried out by Clostridia as well as Enterobacteriaceae. The main intermediate of the oxidative pathway is pyruvate, the further utilization of which produces CO2, H2, acetate, butyrate, ethanol, butanol and 2,3-butanediol. In addition, lactate and succinate are generated. The yield of 1,3-PD per glycerol is determined by the availability of NADH2, which is mainly affected by the product distribution (of the oxidative pathway) and depends first of all on the microorganism used but also on the process conditions (type of fermentation, substrate excess, various inhibitions). In the past decade, research to produce 1,3-PD microbially was considerably expanded as the diol can be used for various polycondensates. In particular, polyesters with useful properties can be manufactured. A prerequisite for making a “green” polyester is a more cost-effective production of 1,3-PD, which, in practical terms, can only be achieved by using an alternative substrate, such as glucose instead of glycerol. Therefore, great efforts are now being made to combine the pathway from glucose to glycerol successfully with the bacterial route from glycerol to 1,3-PD. Thus, 1,3-PD may become the first bulk chemical produced by a genetically engineered microorganism.

Multiple product inhibition and growth modeling of clostridium butyricum and klebsiella pneumoniae in glycerol fermentation

Abstract: The inhibition potentials of products and substrate on the growth ofClostridium butyricum and Klebsiella pneumoniae in the glycerol fermentation are examined from experimental data and with a mathematicalmodel. Whereas the inhibition potential of externally added and self-produced 1,3-propanediol is essentially the same, butyric acid produced by the culture is more toxic than that externally added. The same seems to apply for acetic acid. The inhibitory effect of butyric acid is due tothe total concentration instead of its undissociated form. For acetic acid, it cannot be distinguished between the total concentration and the undissociated formThe inhibition effects of products and substrate in the glycerol fermentation are irrespective of the strains, and, therefore, the same growth model can be used. The maximum product concentrations tolerated (critical concentrations C(*) (pi)) are 0.35 g/Lfor undissociated acetic acid, 10.1 g/L for total butyric acid, 16.6 g/L for ethanol, 71.4 g/L for 1,3-propanediol, and 187.6 g/L for glycerol, which are applicable to C. butyricum and K. pneumoniae grown under a variety of conditions. For 55 steady-states, which were obtained from different types of continuous cultures over a pHrange of 5.3-8.5 and under both substrate limitation and substrate excess, the proposed growth model fits the experimental data with an average deviation of 17.0%. The deviation of model description from experimental values reduces of 11.4% if only the steady-states with excessive substrate are considered. (c) 1994 John Wiley & Sons, Inc.

Fermentation of glycerol to 1,3-propanediol and 2,3-butanediol by Klebsiella pneumoniae

Abstract: Klebsiella pneumoniae was shown to convert glycerol to 1,3-propanediol, 2,3-butanediol and ethanol under conditions of uncontrolled pH. Formation of 2,3-butanediol starts with some hours' delay and is accompanied by a reuse of the acetate that was formed in the first period. The fermentation was demonstrated in the type strain of K. pneumoniae, but growth was better with the more acid-tolerant strain GT1, which was isolated from nature. In continuous cultures in which the pH was lowered stepwise from 7.3 to 5.4, 2,3-butanediol formation started at pH 6.6 and reached a maximum yield at pH 5.5, whereas formation of acetate and ethanol declined in this pH range. 2,3-Butanediol and acetoin were also found among the products in chemostat cultures grown at pH 7 under conditions of glycerol excess but only with low yields. At any of the pH values tested, excess glycerol in the culture enhanced the butanediol yield. Both effects are seen as a consequence of product inhibition, the undissociated acid being a stronger trigger than the less toxic diols and acid anions. The possibilities for using the fermentation type described to produce 1,3-propanediol and 2,3-butanediol almost without by-products are discussed.

Effect of oxygen on formation and structure of Azotobacter vinelandii alginate and its role in protecting nitrogenase.

Abstract: The activity of nitrogenase in the nitrogen-fixing bacteriumAzotobacter vinelandii grown diazotrophically under aerobic conditions is generally considered to be protected against O2 by a high respiration rate. In this work, we have shown that a high rate of respiration is not the prevailing mechanism for nitrogenase protection in A. vinelandii grown in phosphate-limited nitrogen-free chemostat culture. Instead, the formation of alginate appeared to play a decisive role in protecting the nitrogenase that is required for cell growth in this culture. Depending on the O2 tension and cell growth rate, the formation rate and composition of alginate released into the culture broth varied significantly. Furthermore, transmission electron microscopic analysis of cell morphology and the cell surface revealed the existence of an alginate capsule on the surface of A. vinelandii. The composition, thickness, and compactness of this alginate capsule also varied significantly. In general, increasing O2 tension led to the formation of alginate with a higher molecular weight and a greater l-guluronic acid content. The alginate capsule was accordingly thicker and more compact. In addition, the formation of the alginate capsule was found to be strongly affected by the shear rate in a bioreactor. Based on these experimental results, it is suggested that the production of alginate, especially the formation of an alginate capsule on the cell surface, forms an effective barrier for O2 transfer into the cell. It is obviously the quality, not the quantity, of alginate that is decisive for the protection of nitrogenase.

Modeling and simulation of genetic regulatory systems: a literature review.

Abstract: The spatiotemporal expression of genes in an organism is determined by regulatory systems that involve a large number of genes connected through a complex network of interactions. As an intuitive understanding of the behavior of these systems is hard to obtain, computer tools for the modeling and simulation of genetic regulatory networks will be indispensable. This report reviews formalisms that have been employed in mathematical biology and bioinformatics to describe genetic regulatory systems, in particular directed graphs, Bayesian networks, ordinary and partial differential equations, stochastic equations, Boolean networks and their generalizations, qualitative differential equations, and rule-based formalisms. In addition, the report discusses how these formalisms have been used in the modeling and simulation of regulatory systems.

OptKnock: A Bilevel Programming Framework for Identifying Gene Knockout Strategies for Microbial Strain Optimization

Abstract: The advent of genome-scale models of metabo- lism has laid the foundation for the development of computational procedures for suggesting genetic manipu- lations that lead to overproduction. In this work, the computational OptKnock framework is introduced for suggesting gene deletion strategies leading to the over- production of chemicals or biochemicals in E. coli. This is accomplished by ensuring that a drain towards growth resources (i.e., carbon, redox potential, and energy) must be accompanied, due to stoichiometry, by the production of a desired product. Computational results for gene de- letions for succinate, lactate, and 1,3-propanediol (PDO) production are in good agreement with mutant strains published in the literature. While some of the suggested deletion strategies are straightforward and involve elimi- nating competing reaction pathways, many others suggest complex and nonintuitive mechanisms of compensating for the removed functionalities. Finally, the OptKnock procedure, by coupling biomass formation with chemical production, hints at a growth selection/adaptation sys- tem for indirectly evolving overproducing mutants. B 2003 Wiley Periodicals. Biotechnol Bioeng 85: 000-000, 2003.