Showing papers by "DECHEMA published in 2014"

Electroactive bacteria—molecular mechanisms and genetic tools

Abstract: In nature, different bacteria have evolved strategies to transfer electrons far beyond the cell surface. This electron transfer enables the use of these bacteria in bioelectrochemical systems (BES), such as microbial fuel cells (MFCs) and microbial electrosynthesis (MES). The main feature of electroactive bacteria (EAB) in these applications is the ability to transfer electrons from the microbial cell to an electrode or vice versa instead of the natural redox partner. In general, the application of electroactive organisms in BES offers the opportunity to develop efficient and sustainable processes for the production of energy as well as bulk and fine chemicals, respectively. This review describes and compares key microbiological features of different EAB. Furthermore, it focuses on achievements and future prospects of genetic manipulation for efficient strain development.

How Green is Biocatalysis? To Calculate is To Know

Abstract: Green chemistry aims to minimize the environmental hazards of chemical processes and their products. Ever since its introduction by Anastas, this principle has inspired researchers to critically rethink chemistry in view of its potential impact on the environment. Especially, the 12 Principles of Green Chemistry have been an inspiring guideline for this process. Biocatalysis is widely considered as one of the key technologies fulfilling the 12 principles and thereby being green chemistry per se. The reader will recognize stereotypical boilerplate statements such as “enzymes as renewable and biodegradable catalysts”, “working under environmentally benign conditions (temperature, pH, etc.)”, and “operating in water as an environmentally benign solvent” frequently found in the introductory passages to biocatalysis publications. Indeed, these are important parameters that can make biocatalysis environmentally more acceptable than “classical” chemical methods, provided the advantages are not (over)compensated by the disadvantages. Unfortunately, the latter are discussed to a much lesser extent. We also noted a certain tendency to pick a few of the 12 principles to underline the greenness of the method published, which certainly is in contrast to the envisioned use of the 12 principles as a cohesive system. We believe that the time is now to transition from just claiming environmental benefits of (bio)catalysis to quantifying the environmental impact. Indeed, the potential of biocatalysis as a tool to make chemical processes greener has been demonstrated by a limited number of studies. These studies mostly comprise the life-cycle assessment (LCA) of the processes. Unfortunately, LCAs are still rather complex and work intensive. Therefore, LCAs are appreciated by industry to evaluate existing processes (and to use the positive result as a selling argument), whereas research-oriented academic groups generally do not possess the expertise, resources, and interest to perform LCAs. As a result, sustainability issues are often addressed in the phase of manuscript preparation as described above. We believe that on the long term, careless, qualitative use of the term green chemistry will discredit the concept. Therefore, with this contribution we wish to promote the use of simple metrics to assess the environmental footprint of a given method in a semi-quantitative way. To calculate is to know (better). Sheldon proposed the E factor (environmental factor) to assess the greenness of a given reaction. The E factor denotes the amount of waste generated per product equivalent [Eq. (1)] .

De novo production of the monoterpenoid geranic acid by metabolically engineered Pseudomonas putida

Abstract: Production of monoterpenoids as valuable chemicals using recombinant microbes is a growing field of interest. Unfortunately, antimicrobial activity of most monoterpenoids hampers a wide application of microorganisms for their production. Strains of Pseudomonas putida, a fast growing and metabolically versatile bacterium, often show an outstanding high tolerance towards organic solvents and other toxic compounds. Therefore, Pseudomonas putida constitutes an attractive alternative host in comparison to conventionally used microorganisms. Here, metabolic engineering of solvent tolerant Pseudomonas putida as a novel microbial cell factory for de novo production of monoterpenoids is reported for the first time, exemplified by geranic acid production from glycerol as carbon source. The monoterpenoic acid is an attractive compound for application in the flavor, fragrance, cosmetics and agro industries. A comparison between Escherichia coli, Saccharomyces cerevisiae and Pseudomonas putida concerning the ability to grow in the presence of geranic acid revealed that the pseudomonad bears a superior resilience compared to the conventionally used microbes. Moreover, Pseudomonas putida DSM 12264 wildtype strain efficiently oxidized externally added geraniol to geranic acid with no further degradation. Omitting external dosage of geraniol but functionally expressing geraniol synthase (GES) from Ocimum basilicum, a first proof-of-concept for de novo biosynthesis of 1.35 mg/L geranic acid in P. putida DSM 12264 was achieved. Doubling the amount of glycerol resulted in twice the amount of product. Co-expression of the six genes of the mevalonate pathway from Myxococcus xanthus to establish flux from acetyl-CoA to the universal terpenoid precursor isopentenylpyrophosphate yielded 36 mg/L geranic acid in shake flask experiments. In the bioreactor, the recombinant strain produced 193 mg/L of geranic acid under fed-batch conditions within 48 h. Metabolic engineering turned Pseudomonas putida DSM 12264, a versatile monoterpenoid oxidation biocatalyst, into an efficient microbial cell factory for de novo geranic acid production. Improvements by metabolic and process engineering are expected to further increase the product concentration. To the best of the authors’ knowledge, this is the first example of a de novo production of a monoterpenoid with Pseudomonas putida and of a microbial monoterpenoic acid synthesis in general.

Nanoscale zero-valent iron flakes for groundwater treatment

Abstract: Even today the remediation of organic contaminant source zones poses significant technical and economic challenges. Nanoscale zero-valent iron (NZVI) injections have proved to be a promising approach especially for source zone treatment. We present the development and the characterization of a new kind of NZVI with several advantages on the basis of laboratory experiments, model simulations and a field test. The developed NZVI particles are manufactured by milling, consist of 85 % Fe(0) and exhibit a flake-like shape with a thickness of <100 nm. The mass normalized perchloroethylene (PCE) dechlorination rate constant was 4.1 × 10−3 L/g h compared to 4.0 × 10−4 L/g h for a commercially available reference product. A transport distance of at least 190 cm in quartz sand with a grain size of 0.2–0.8 mm and Fe(0) concentrations between 6 and 160 g/kg (sand) were achieved without significant indications of clogging. The particles showed only a low acute toxicity and had no longterm inhibitory effects on dechlorinating microorganisms. During a field test 280 kg of the iron flakes was injected to a depth of 10–12 m into quaternary sand layers with hydraulic conductivities ranging between 10−4 and 10−5 m/s. Fe(0) concentrations of 1 g/kg (sand) or more [up to 100 g/kg (sand)] were achieved in 80 % of the targeted area. The iron flakes have so far remained reactive for more than 1 year and caused a PCE concentration decrease from 20.000–30.000 to 100–200 µg/L. Integration of particle transport processes into the OpenGeoSys model code proved suitable for site-specific 3D prediction and optimization of iron flake injections.

Thioesterases for ethylmalonyl–CoA pathway derived dicarboxylic acid production in Methylobacterium extorquens AM1

Abstract: The ethylmalonyl–coenzyme A pathway (EMCP) is a recently discovered pathway present in diverse α-proteobacteria such as the well studied methylotroph Methylobacterium extorquens AM1. Its glyoxylate regeneration function is obligatory during growth on C1 carbon sources like methanol. The EMCP contains special CoA esters, of which dicarboxylic acid derivatives are of high interest as building blocks for chemical industry. The possible production of dicarboxylic acids out of the alternative, non-food competing C-source methanol could lead to sustainable and economic processes. In this work we present a testing of functional thioesterases being active towards the EMCP CoA esters including in vitro enzymatic assays and in vivo acid production. Five thioesterases including TesB from Escherichia coli and M. extorquens, YciA from E. coli, Bch from Bacillus subtilis and Acot4 from Mus musculus showed activity towards EMCP CoA esters in vitro at which YciA was most active. Expressing yciA in M. extorquens AM1 led to release of 70 mg/l mesaconic and 60 mg/l methylsuccinic acid into culture supernatant during exponential growth phase. Our data demonstrates the biotechnological applicability of the thioesterase YciA and the possibility of EMCP dicarboxylic acid production from methanol using M. extorquens AM1.

Improving 2-phenylethanol and 6-pentyl-α-pyrone production with fungi by microparticle-enhanced cultivation (MPEC).

Abstract: Trichoderma atroviride IMI 206040 synthesizes the coconut lactone 6-pentyl-α-pyrone (6-PAP) de novo and Aspergillus niger DSM 821 produces the rose-like flavour compound 2-phenylethanol (2-PE) from the precursor l-phenylalanine. Here, microparticles of different chemical composition and nominal particle diameter in the range 5–250 µm were added to shake-flask cultures of both fungi to investigate the particles' effect on product formation. Maximum 2-PE concentration increased by a factor of 1.3 to 1430 mg/l with the addition of 2% w/v talc (40 µm diameter). Maximum 6-PAP concentration increased by a factor of 2 to 40 mg/l with the addition of 2% w/v iron (II, III) oxide. The influence of ions leaching out of the particles was investigated by cultivating the fungi in leached particle medium. For the first time, the positive effect of the microparticle-enhanced cultivation (MPEC) technique on the microbial production of volatile metabolites, here flavour compounds from submerged fungal cultures, is demonstrated. The effect is strain- and particle-specific. Copyright © 2014 John Wiley & Sons, Ltd.

Partial Methylation at Am100 in 18S rRNA of Baker's Yeast Reveals Ribosome Heterogeneity on the Level of Eukaryotic rRNA Modification

Abstract: Ribosome heterogeneity is of increasing biological significance and several examples have been described for multicellular and single cells organisms In here we show for the first time a variation in ribose methylation within the 18S rRNA of Saccharomyces cerevisiae Using RNA-cleaving DNAzymes, we could specifically demonstrate that a significant amount of S cerevisiae ribosomes are not methylated at 2′-O-ribose of A100 residue in the 18S rRNA Furthermore, using LC-UV-MS/MS of a respective 18S rRNA fragment, we could not only corroborate the partial methylation at A100, but could also quantify the methylated versus non-methylated A100 residue Here, we exhibit that only 68% of A100 in the 18S rRNA of Scerevisiae are methylated at 2′-O ribose sugar Polysomes also contain a similar heterogeneity for methylated Am100, which shows that 40S ribosome subunits with and without Am100 participate in translation Introduction of a multicopy plasmid containing the corresponding methylation guide snoRNA gene SNR51 led to an increased A100 methylation, suggesting the cellular snR51 level to limit the extent of this modification Partial rRNA modification demonstrates a new level of ribosome heterogeneity in eukaryotic cells that might have substantial impact on regulation and fine-tuning of the translation process

Electrochemical regeneration of oxidised nicotinamide cofactors in a scalable reactor

Abstract: An efficient and scalable NAD(P)+ regeneration system to promote alcohol dehydrogenase-catalysed oxidation reactions is reported. Indirect electrochemical oxidation of NADH was established with 2,2′-azino-bis-(3 ethyl-benzo-thiazoline-6-sulfonic acid) (ABTS), being the most efficient mediator amongst the candidates screened. ABTS exhibited very high catalytic performance of 1200 catalytic turnovers per hour. In a three-dimensional electrochemical cell with a high working electrode surface area of 24 m2 and optimised concentrations of substrate, enzyme, cofactor and mediator, TTNs of 1860 for the mediator and of 93 for the cofactor were measured. Besides, a maximum STY of 1.4 g l−1 h−1 was determined. Here we show the highest TTN ever reported for a mediated NAD+ regeneration in an electro-enzymatic process. The use of the three-dimensional electrochemical reactor led to an 8-fold improvement of the STY compared to a published system, based on a two-dimensional cell.

Realization of Al/Mg-Hybrid-Joints by Ultrasound Supported Friction Stir Welding - Mechanical Properties, Microstructure and Corrosion Behavior

Abstract: Fusion welding of dissimilar metals is in the most cases difficult or even impossible as a result of different melting points and the development of undesirable brittle intermetallic phases. This often leads to joint strengths considerable below the tensile strength of the base materials. By using Friction Stir Welding (FSW) it is possible to reduce the development of the intermetallic phases of Al/Mg-joints significantly but not to avoid them completely. Hence a hybrid welding system at the WKK of the University of Kaiserslautern was developed called “Ultrasound Supported Friction Stir Welding (US-FSW)” with the aim to shatter the brittle interlayer lines and to scatter fragments in the welding area during the FSW process. Pre-investigations have shown that for Al/Mg-US-FSW-joints the strength can be increased up to 30% in comparison to conventional FSW. Moreover for the reliable detection of nonconformities in the weld during a post-process inspection by suitable non-destructive testing (NDT) methods is necessary. Also there is a strong need for better process monitoring and control by in-process NDT methods. Furthermore the corrosion behavior of the basic materials and hybrid-joints was investigated by electrochemical methods indicating an increased corrosion of the Mg alloy in the area of the Al/Mg-butt weld.

Enantioselective enzymatic synthesis of the α-hydroxy ketone (R)-acetoin from meso-2,3-butanediol

Abstract: Acetoin (3-hydroxy-2-butanone) is an important flavour compound and is applied in cosmetics, pharmacy and chemical synthesis. In contrast to chemical syntheses or fermentations an enzymatic route facilitates enantioselective acetoin production. The discovery of a (S)-selective alcohol dehydrogenase enables a novel production process of (R)-acetoin from meso-2,3-butanediol. It was shown that the regeneration of oxidised nicotinamide adenine dinucleotide is a key point in preparative application of dehydrogenases for the oxidative route. An electrochemical regeneration system was successful combined with the ADH catalysed reaction. Up to 48 mM (R)-acetoin was produced in the reaction system while productivities up to 2 mM h−1 were reached. The possibility to apply an electrochemical system in a semi-preparative synthesis will stimulate further research of electroenzymatic processes with oxidoreductases.

P-LinK: A method for generating multicomponent cytochrome P450 fusions with variable linker length.

Abstract: Fusion protein construction is a widely employed biochemical technique, especially when it comes to multi-component enzymes such as cytochrome P450s. Here we describe a novel method for generating ...

Mediated electron transfer with monooxygenases—Insight in interactions between reduced mediators and the co-substrate oxygen

Abstract: One of the most important obstacles to overcome in biocatalysis with monooxygenases is the enzyme's dependency on the costly redox cofactor NAD(P)H. Electrochemical regeneration systems, in which an electrode serves as electron donor, provide an alternative route to enzymatic redox reactions. Mediators are often used to accelerate electron transfer between electrode and enzyme. We investigated the mediated bioelectrochemical conversion of p-xylene to 2,5-dimethylphenol (2,5-DMP) by a P450 BM3 variant and were able to produce 2,5-DMP electrochemically. Due to the fact that mediator reduction is limited by the electrode surface a scale-up was performed. However, increasing the electrode surface area to reactor volume ratio led to a drastic increase in cathodic oxygen reduction, causing a drop in product formation. It was shown that reduced cobalt sepulchrate reacts with the co-substrate oxygen. Furthermore, the reportedly oxygen stable mediator [Cp*Rh(I)(bpy)H]+ was compared to cobalt sepulchrate. While its turnover frequency is of comparable magnitude to cobalt sepulchrate when transferring the electrons between electrode and enzyme, using NADP+ as intermediary between the mediator and the enzyme significantly increased the mediator's turnover frequency. The rhodium mediator [Cp*Rh(I)(bpy)H]+ does not appear to be significantly more oxygen stable.

On ultra-high temperature oxidation of Cr–Cr3Si alloys: Effect of germanium†

Abstract: The oxidation behavior of Cr–Cr3(Si1−XGeX) alloys with the composition range Cr85GeXSi1−X (0 < X < 15) was studied at 1350 °C. Thermogravimetric measurements showed improved oxidation kinetics by alloying up to 2 at% of Ge, but a significant weight loss was observed when higher Ge was added. Phase analysis and composition of the spalled oxide scales and subscale alloy substrates revealed that eskolaite (Cr2O3) forms the protective scale, while SiO2 (cristobalite) is locally formed below the chromia scale. Addition of up to 2 at% altered the morphology of locally formed silica and subsequently affected the spallation of chromia scale. The morphological observations of the different chromia scales are discussed for all alloys oxidized at 1350 °C.

Light-Accelerated Biocatalytic Oxidation Reactions

Abstract: The influence of (visible) light on the performance of laccase mediator systems (LMS) was investigated. As a model reaction, LMS-mediated nicotinamide adenine dinucleotide (NAD+) regeneration to promote alcohol dehydrogenase catalyzed oxidation reactions was examined.

Environmental impacts of nanomaterials: providing comprehensive information on exposure, transport and ecotoxicity - the project DaNa2.0

Abstract: Background Assessing the impact of new technologies or newly developed substances on our environment is a challenge, even more so if the applied test methods - both toxicological and analytical - are often found to be inadequate and need amendments or even new developments as it is in the case of nanotechnology. This is illustrated by numerous publications in the field of nano-ecotoxicology which although they have been investigating the impact of a number of nanomaterials on several organisms almost never allow for explicit statements on potential hazards of these nanomaterials. This fact not only hampers the knowledge communication to all non-scientists (e.g. consumers) but it also complicates the transfer of the obtained results for other scientists.

Design model for diffusion coatings formed via pack cementation

Abstract: Coatings improve the high temperature corrosion resistance of materials by enriching the subsurface zone with elements that form protective oxide scales, which increase the material lifetime. Interesting coatings are aluminum (Al) diffusion coatings formed in a pack cementation process e.g., on austenitic steels. The coating procedure may lead to the risk of crack formation within the coating because of the detrimental combination of high brittleness of the Al-rich intermetallic phases that form, the coating thickness, and the mismatch of the coefficients of thermal expansion (CTE) between the material and the coating. By means of a new coating design, Al diffusion coatings consisting of less brittle intermetallic phases with a CTE closer to that of the substrate can be applied with a controlled coating thickness. For this purpose, the required coating manufacturing parameters such as process temperature, process time, and powder composition are predicted by the presented coating design model.

Introduction: The Need for Risk-Informed River Basin Management

Abstract: As the pressures from both anthropogenic and natural causes on environmental systems increase, it is no longer effective or efficient to deal with one issue at a time, since solving a singular problem often causes damaging impacts on other environmental compartments or in other places. We must consider the consequences of our actions on all parts of the environment in an integrated way and configure these actions to cope with an uncertain future. These challenges demand a different approach in order to achieve actual improvement of the ecological quality of our river basins and thus sustain the goods and services they provide for the well-being of society. Risk-informed management is this new approach. It involves the integrated application of three key principles: be well informed, manage adaptively and take a participatory approach. This chapter introduces this risk-informed management approach as it was developed in the European Commission funded project RISKBASE and provides an introduction to rest of this book where the key principles are explained and underpinned in detail.

The influence of copper in ash deposits on the corrosion of boiler tube alloys for waste‐to‐energy plants

Abstract: Previous laboratory studies reported in the literature and field experience have revealed the accelerating effect of the heavy metals lead and zinc on the corrosion behaviour of materials used in waste incineration plants. The major problem is that heavy metal containing chloride and sulphate salts usually have relatively low melting points, often below the metal temperature of the boiler surfaces. While the negative influence of lead and zinc is well-known, copper is another heavy metal that can occur in high amounts of up to 2000 mg/kg in refuse-derived fuel, which is the fuel produced by shredding and dehydrating solid municipal waste that is burned in modern waste-to-energy plants. The impact of copper additions on the corrosion behaviour of one iron-based austenitic alloy 1.4952 and three nickel-based alloys 2.4856 (alloy 625), 2.4633 (alloy 602 CA), 2.4605 (alloy 59), which are often used in waste incineration plants was investigated. The results of these studies clearly show the strong corrosive effect of copper content in salt mixtures on the corrosion of steels and nickel-based alloys.

Methanol Utilisation Technologies

Abstract: Oil and gas are raw materials—the availability of which is prognosticated to run short in the near future. The peak oil discussion is an example generally perceived as proof of this development to come.

Herstellung von Grundchemikalien auf Basis nachwachsender Rohstoffe als Alternative zur Petrochemie

Abstract: Die derzeitige Entwicklung in den USA, gepragt durch billiges Schiefergas, hat starke Auswirkungen auf die Produktion von Basischemikalien. Der Beitrag geht der Frage nach, ob sich vor diesem Hintergrund der Anteil nachwachsender Rohstoffe fur die Chemikalienproduktion steigern lasst oder ob sich die Zahl biobasierter Produkte und Verfahren eher verringern wird. Antworten liefert fur einige ausgewahlte Grundchemikalien der Vergleich von bestehenden Produktionsverfahren auf petrochemischer Basis mit Alternativen auf Basis nachwachsender oder anderer fossiler Rohstoffe (bspw. Methan und niedere Alkane).

Cr-Ge-Si Alloys for High-Temperature Structural Applications: Microstructural Evolution

Abstract: The microstructural evolution of Cr-Si1−x-Gex (0 < x < 15 at. pct) alloys was studied (in annealed state). The quasi-isothermal section of the ternary diagram was assessed by quantitative EPMA analysis. Morphology, phase formation, chemical distribution, and indentation hardness of the alloys were investigated as a function of Ge/Si ratio. The microstructure of all studied alloys consisted of Crss solid solution and A15 Cr3X intermetallic phases. Substitution of Si by Ge strongly altered the microstructure by transforming the morphology from a lamellar eutectic Cr-Cr3Si system toward a peritectic one with dispersed Crss phase in A15 matrix. EPMA chemical distribution maps and X-ray diffraction results prove the mutual solubility of Si and Ge in A15 phase by forming Cr3(Si,Ge) as a complex A15 structure with Cr3(Si1−xGex) composition. Precipitates of the intermetallic phase within the Crss phase was observed in Ge-alloyed samples. Indentation hardness results showed that upon Si-Ge substitution the hardness of both phases was reduced. However, Si substitution by Ge had a stronger influence on the hardness of the solid solution phase than on the intermetallic phase.