248 research outputs found
Carsten Holtmann and Dirk Neumann Market and Firm – Two Sides of a Coin 1
No full textElectronic markets are not just evolving they are designed. As such providing electronic trading venues is an entrepreneurial activity. The institutional approach followed here introduces a market operator as an economic player. As the entrepreneur charges fees for his service of operating an electronic market, the transaction cost savings incurred by information technology are essentially fully shifted to the market participants. As such the momentum predicted by the Electronic Market Hypothesis is limited in practice. The paper addresses this gap by deriving a conceptual framework, which reconciles the classical view on electronic markets with the entrepreneurial view.
Elektrochemisches Monitoring mikrobieller Aktivität : Grundlagen und Anwendung in der Abwasserreinigung
No full textvon Dirk Holtman
Intensivierung von enzymkatalysierten Reaktionen
No full textProcess intensification aims at enabling bridging the gap between fundamental research such as identification of new catalysts and reactions and their implementation in industrial environments. Especially the field of biocatalysis has seen some tremendous improvements and the development of new tools and approaches to bridge this gap. In this contribution we highlight some recent developments as selected case studies.BT/Biocatalysi
The Oxygen Dilemma: A Severe Challenge for the Application of Monooxygenases?
No full textMonooxygenases are promising catalysts because they in principle enable the organic chemist to perform highly selective oxyfunctionalisation reactions that are otherwise difficult to achieve. For this, monooxygenases require reducing equivalents, to allow reductive activation of molecular oxygen at the enzymes' active sites. However, these reducing equivalents are often delivered to O2 either directly or via a reduced intermediate (uncoupling), yielding hazardous reactive oxygen species and wasting valuable reducing equivalents. The oxygen dilemma arises from monooxygenases' dependency on O2 and the undesired uncoupling reaction. With this contribution we hope to generate a general awareness of the oxygen dilemma and to discuss its nature and some promising solutions.BT/Biocatalysi
Light-driven bioprocesses
No full textEnzyme catalysis and photocatalysis are two research areas that have become of major interest in organic synthesis. This is mainly because both represent attractive strategies for making chemical synthesis more efficient and sustainable. Because enzyme catalysis offers several inherent advantages, such as high substrate specificity, regio-, and stereoselectivity, and activity under environmentally benign reaction conditions, biocatalysts are increasingly being adopted by the pharmaceutical and chemical industries. In addition, photocatalysis has proven to be a powerful approach for accessing unique reactivities upon light irradiation and performing reactions with an extended substrate range under milder conditions compared to light-independent alternatives. It is therefore not surprising that bio-and photocatalytic approaches are now often combined to exploit the exquisite selectivity of enzymes and the unique chemical transformations accessible to photocatalysis. In this chapter, we provide an overview of the wide variety of lightdriven bioprocesses, ranging from photochemical delivery of reducing equivalents to redox enzymes, photochemical cofactor regeneration, to direct photoactivation of enzymes. We also highlight the possibility of catalyzing non-natural reactions via photoinduced enzyme promiscuity and the combination of photo-and biocatalytic reactions used to create new synthetic methodologies.</p
Effects of particle addition to Streptomyces cultivations to optimize the production of actinorhodin and streptavidin
No full textHoltmann D, Vernen F, Müller J, et al. Effects of particle addition to Streptomyces cultivations to optimize the production of actinorhodin and streptavidin. Sustainable Chemistry and Pharmacy. 2016;5:67-71
Mehr machen mit weniger: Intensivierung von Ganzzell-Bioprozessen
No full textIn chemical process engineering, process intensification (PI) has proven itself as a method that resulted very often in processes with an at least doubled process performance. In recent years, the PI techniques have found more and more applications in biotechnology. Exemplary continuous processes, single-use reactors, electrobiotechnology and hybrid techniques are discussed here.BT/Biocatalysi
Investigation of vitamin B12 biosynthesis by known and newly identified bacterial strains
No full textVitamin B12 (cobalamin) is an essential nutrient playing an important role in many crucial processes in the human body. Due to such essential requirement, the demand for vitamin B12 and thereby interest in alternative efficient vitamin B12 sources is growing.
The importance of vitamin B12 became clear in the 1920s after two American physicians, Minot and Murphy, demonstrated the role of their so-called “extrinsic factor” in the treatment of pernicious anemia. After years of further research, the complete chemical synthesis of cobalamin was achieved by Woodward and Eschenmoser in 1972. However, due to the very complex chemical structure of vitamin B12, the described synthesis procedure included about 70 steps, which makes it economically disadvantageous. For this reason, microbial synthesis is used as the exclusive strategy for industrial vitamin B12 production nowadays.
Although there are several vitamin B12 - producing bacterial species known, there are differences in the type of the compound synthesized by different strains. For example, Propionibacterium freudenreichii (formerly P. shermanii) is well known for its ability to synthesize the active form of vitamin B12, while production of a vitamin B12 analogue called pseudovitamin B12 was shown for Lactobacillus species. The two forms differ in their chemical structure, which makes pseudovitamin B12 inactive as a cofactor for human enzymes. Hence, if the goal is to produce vitamin B12 for human nutrition purposes, it is important to determine the type of the cobalamin synthesized by the microorganisms.
Various methods of vitamin B12 analysis have been described, which differ in their sensitivity and ability to discriminate between the vitamin B12 forms. The classical microbiological assay (MBA) is known to respond not only to vitamin B12 but also to its analogues, while HPLC - based methods possess the required specificity.
In this work, a sensitive and reliable LC-MS/MS method for the identification and quantification of vitamin B12 was developed which not only allows vitamin B12 quantification, but also enables clear discrimination between its active and inactive form. The developed method was successfully applied for the quantitative comparison of the well - known vitamin B12 - producing species and for the analysis of the active vitamin B12 production in the newly selected candidate strains. Different strategies for the identification of new producing bacterial strains were proposed in this work which resulted in the description of bacteria with the ability to selectively produce high levels of active vitamin B12 under aerobic conditions. Among the identified strains, Terrabacter sp. DSM 102553 and Hyphomicrobium sp. DSM 3646 proved to be the most promising cobalamin-producing strains. Cobalamin synthesis with the identified bacteria in different media was investigated, which resulted in identification of low-cost media enabling accumulation of high vitamin B12 yields. The relatively high vitamin B12 concentrations achieved with the strains in simple cultivation experiments performed in low-cost media open new opportunities for a cost-effective biotechnological vitamin B12 production.Bundeslände
Reactors for microbial electrobiotechnology
No full textFrom the first electromicrobial experiment to a sophisticated microbial electrochemical process - it all takes place in a reactor. Whereas the reactor design and materials used strongly influence the obtained results, there are no common platforms for MES reactors. This is a critical convention gap, as cross-comparison and benchmarking among MES as well as MES vs. conventional biotechnological processes is needed. Only knowledge driven engineering of MES reactors will pave the way to application and commercialization. In this chapter we first assess the requirements on reactors to be used for bioelectrochemical systems as well as potential losses caused by the reactor design. Subsequently, we compile the main types and designs of reactors used for MES so far, starting from simple H-cells to stirred tank reactors. We conclude with a discussion on the weaknesses and strengths of the existing types of reactors for bioelectrochemical systems that are scored on design criteria and draw conclusions for the future engineering of MES reactors. [GRAPHICS]
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