Alcohol production through volatile fatty acids reduction with hydrogen as electron donor by mixed cultures

In this research we demonstrated a new method to produce alcohols. It was experimentally feasible to produce ethanol, propanol and butanol from solely volatile fatty acids (VFAs) with hydrogen as electron donor. In batch tests, VFAs such as acetic, propionic and butyric acids were reduced by mixed microbial cultures with a headspace of 1.5 bar of hydrogen. Observed alcohol concentrations were 3.69 ± 0.25 mM of ethanol, 8.08 ± 0.85 mM of propanol and 3.66 ± 0.05 mM of n-butanol. The conversion efficiency based on the electron balance was 55.1 ± 5.6% with acetate as substrate, 50.3 ± 4.7% with propionate and 46.7 ± 2.2% with n-butyrate. Methane was the most predominant by-product in each batch experiment, 33.6 ± 9.6% of VFA and hydrogen was converted to methane with acetate as substrate; which was 27.1 ± 7.1% with propionate and 36.6 ± 2.2% with n-butyrate. This VFAs reducing renewable fuel production process does not require carbohydrates like fermentable sugars, but uses biomass with high water content or low sugar content that is unsuitable as feedstock for current fermentation processes. This so-called low-grade biomass is abundantly present in many agricultural areas and is economically very attractive feedstock for the production of biofuels.     

Hydrogen production with a microbial biocathode

This paper, for the first time, describes the development of a microbial biocathode for hydrogen production that is based on a naturally selected mixed culture of electrochemically active micro-organisms. This is achieved through a three-phase biocathode startup procedure that effectively turned an acetate- and hydrogen-oxidizing bioanode into a hydrogen-producing biocathode by reversing the polarity of the electrode. The microbial biocathode that was obtained in this way had a current density of about -1.2 A/Nm2 at a potential of -0.7 V. This was 3.6 times higher than that of a control electrode (-0.3 A/m2). Furthermore, the microbial biocathode produced about 0.63 m3 H2/m3 cathode liquid volume/day at a cathodic hydrogen efficiency of 49% during hydrogen yield tests, whereas the control electrode produced 0.08 m3 H2/m3 cathode liquid volume/day at a cathodic hydrogen efficiency of 25%. The effluent of the biocathode chamber could be used to inoculate another electrochemical cell that subsequently also developed an identical hydrogen-producing biocathode (-1.1 A/m2 at a potential of -0.7 V). Scanning electron micrographs of both microbial biocathodes showed a well-developed biofilm on the electrode surface.     

Function of the fully conserved residues Asp99, Tyr52 and Tyr73 in phospholipase A2

In the active centre of pancreatic phospholipase A₂ His48 isat hydrogen-bonding distance to Asp99. This Asp-His couple isassumed to act together with a water molecule as a catalytictriad. Asp99 is also linked via an extended hydrogen bondingsystem to the side chains of Tyr52 and Tyr73. To probe the functionof the fully conserved Asp99, Tyr52 and Tyr73 residues in phospholipaseA₂, the Asp99 residue was replaced by Asn, and each of the twotyrosines was separately replaced by either a Phe or a Gln.The catalytic and binding properties of the Phe52 and Phe73mutants did not change significantly relative to the wild-typeenzyme. This rules out the possibility that either one of thetwo Tyr residues in the wild-type enzyme can function as anacyl acceptor or proton donor in catalysis. The Gln73 mutantcould not be obtained in any significant amounts probably dueto incorrect folding. The Gln52 mutant was isolated in low yield.This mutant showed a large decrease in catalytic activity whileits substrate binding was nearly unchanged. The results suggesta structural role rather than a catalytic function of Tyr52and Tyr73. Substitution of asparagine for aspartate hardly affectsthe binding constants for both monomeric and micellar substrateanalogues. Kinetic characterization revealed that the Asn99mutant has retained no less than 65% of its enzymatic activityon the monomeric substrate rac 1,2-dihexanoyldithio-propyl-3-phosphocholine,probably due to the fact that during hydrolysis of monomericsubstrate by phospholipase A₂ proton transfer is not the rate-limitingstep. The Asp to Asn substitution decreases the catalytic rateon micellar 1,2-dioctanoyl-sn-glycero-3-phosphocholine 25-fold.To explain this remaining activity we suggest that in the mutantthe Asn99 orients His48 in the same way as Asp99 orients His48in native phospholipase A₂ and that the lowered activity iscaused by a reduced stabilization of the transition state.     

Mating stimulant of the pine weevilHylobius abietis (L.)

Factors eliciting copulatory behavior in mature maleHylobius abietis were studied in the laboratory. Dead female weevils were sexually attractive, while dead mature males and pentane-extracted female weevils were not. The sexual attractiveness of dead females declined with time after death. Pentane extracts of whole female weevils or of the anterior or posterior parts of their bodies elicited a copulatory response when applied to decoys. In contrast, extracts of hindgut or frass were inactive. Juvenile males were sexually attractive for about four weeks, after which their attractiveness gradually declined. The results indicate that the mating stimulant is present on the body surface of female and juvenile male weevils, and it can be extracted with pentane.     

Development of a countergradient parking system for gradient liquid chromatography with online biochemical detection of serine protease inhibitors

A gradient HPLC approach in combination with a countergradient system for online biochemical detection (BCD) to screen for inhibitors of serine proteases is described. For gradient separations, this novel countergradient system was developed to produce a biocompatible constant solvent composition in the BCD. The countergradient system is based on retaining complete gradients in an additional preparative HPLC column, followed by subsequent and reversible elution to the separation column effluent. Major advantages compared with existing countergradient systems are that no additional LC pumps are needed and enhanced stability. The developed countergradient system was systematically characterized applying different gradient programs. Inhibitors eluting in a postcolumn continuous flow analysis interfere with the enzymatic release of fluorescent 7-amino-4-methylcoumarin (AMC) from an AMC-labeled peptide. The inhibitory activity of eluting substances is sensitively detected as the degree of reduced fluorescence intensity. This biochemical detection system (BCD) for proteases was validated with three known inhibitors of the benzamidine type. Their IC 50 values were in good accordance with the results of conventional plate reader assays. Finally, a small library of protease inhibitors was successfully screened with the combination of the BCD and the countergradient system.     

Highly Stable Red‐Emitting Sr2Si5N8:Eu2+ Phosphor with a Hydrophobic Surface

One of the biggest problems in white light‐emitting diodes (WLEDs) is the moisture‐induced degradation of phosphors. This paper proposes a simple and feasible surface modification method to solve it, whereby a hydrophobic surface layer is developed on the surface of the phosphors. The particular case of orange‐red‐emitting Sr₂Si₅N₈:Eu²⁺ (SSN) phosphor was investigated. The mechanism to develop the hydrophobic layer involves hydrolysis and polymerization of tetraethylorthosilicate (TEOS) and polydimethylsiloxane (PDMS). The experimental results showed that the surface layer of SSN phosphor was successfully modified to a hydrophobic nanolayer (8 nm) of amorphous silicon dioxide that contains CH₃ groups in the surface. This hydrophobic surface layer gives the modified phosphor superior stability in high‐pressure water steam conditions at 150°C.     

Reinforcement learning for robot soccer

Batch reinforcement learning methods provide a powerful framework for learning efficiently and effectively in autonomous robots. The paper reviews some recent work of the authors aiming at the successful application of reinforcement learning in a challenging and complex domain. It discusses several variants of the general batch learning framework, particularly tailored to the use of multilayer perceptrons to approximate value functions over continuous state spaces. The batch learning framework is successfully used to learn crucial skills in our soccer-playing robots participating in the RoboCup competitions. This is demonstrated on three different case studies.

Ultra compact multitip scanning tunneling microscope with a diameter of 50 mm

We present a multitip scanning tunneling microscope (STM) where four independent STM units are integrated on a diameter of 50 mm. The coarse positioning of the tips is done under the control of an optical microscope or scanning electron microscopy in vacuum. The heart of this STM is a new type of piezoelectric coarse approach called KoalaDrive. The compactness of the KoalaDrive allows building a four-tip STM as small as a single-tip STM with a drift of less than 0.2 nm/min at room temperature and lowest resonance frequencies of 2.5 kHz (xy) and 5.5 kHz (z). We present as examples of the performance of the multitip STM four point measurements of silicide nanowires and graphene.