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Eleven bacteria capable of utilizing cyanophycin (cyanophycin granule polypeptide (CGP)) as a carbon source for growth were isolated. One isolate was taxonomically affiliated as Pseudomonas anguilliseptica strain BI, and the extracellular cyanophycinase (CphE) was studied because utilization of cyanophycin as a carbon source and extracellular cyanophycinases were hitherto not described. CphE was detected in supernatants of CGP cultures and purified from a corresponding culture of strain BI employing chromatography on the anion exchange matrix Q-Sepharose and on an arginine-agarose affinity matrix. The mature form of the inducible enzyme consisted of one type of subunit with M(r) = 43,000 and exhibited high specificity for CGP, whereas proteins and synthetic polyaspartic acid were not hydrolyzed or were only marginally hydrolyzed. Degradation products of the enzyme reaction were identified as aspartic acid-arginine dipeptides (beta-Asp-Arg) by high performance liquid chromatography and electrospray ionization mass spectrometry. The corresponding gene (cphE, 1254 base pairs) was identified in subclones of a cosmid gene library of strain BI by heterologous active expression in Escherichia coli, and its nucleotide sequence was determined. The enzyme exhibited only 27-28% amino acid sequence identity to intracellular cyanophycinases occurring in cyanobacteria. Analysis of the amino acid sequence of cphE revealed a putative catalytic triad consisting of the motif GXSXG plus a histidine and most probably a glutamate residue. In addition, the strong inhibition of the enzyme by Pefabloc((R)) and phenylmethylsulfonyl fluoride indicated that the catalytic mechanism of CphE is related to that of serine type proteases. Quantitative analysis on the release of beta-Asp-Arg dipeptides from C-terminal labeled CGP gave evidence for an exo-degradation mechanism.

In recent years the interest in materials with specific adjustable properties has increased due to higher requirements on the material performance. Here a smart composite material is to be developed, whose stiffness can be varied subjected to a magnetic field. To realise this aim a magnetorheological fluid (MRF) embedded in a polymeric matrix material is considered. To model the material behaviour of the composite a homogenisation method will be applied. Amongst others this requires the knowledge of the multiaxial material behaviour of each constituent. The modelling of the material behaviour of MRF under shear deformation, which is the aim of this work, represents the first step in this process. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

In this contribution a modelling approach using numerical homogenisation techniques is applied to predict the effective nonlinear material behaviour of composites from simulations of a representative volume element (RVE). Numerical models of the heterogeneous material structure in the RVE are generated using the eXtended Finite Element Method (XFEM) which allows for a regular mesh. Suitable constitutive relations account for the material behaviour of the constituents. The influence of the nonlinear matrix material behaviour on the composite is studied in a physically nonlinear FE simulation of the local material behaviour in the RVE ­ effective stress-strain curves are computed and compared to experimental observations. The approach is currently augmented by a damage model for the fibre bundle. (© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Extended abstract of a paper presented at Microscopy and Microanalysis 2010 in Portland, Oregon, USA, August 1 – August 5, 2010.

Extended abstract of a paper presented at Microscopy and Microanalysis 2010 in Portland, Oregon, USA, August 1 – August 5, 2010.

For a consistent lightweight design the consideration of the nonlinear macroscopic material behaviour of composites, which is amongst others driven by damage and strain-rate effects on the mesoscale, is required. Therefore, a modelling approach using numerical homogenization techniques is applied to predict the effective nonlinear material behaviour of the composite based on the finite element simulation of a representative volume element (RVE). In this RVE suitable constitutive relations account for the material behaviour of each constituents. While the reinforcing glass fibres are assumed to remain linear elastic, a viscoplastic constitutive law is applied to represent the strain-rate dependent, inelastic deformation of the matrix material. In order to analyse the influence of the nonlinear matrix material behaviour on the global mechanical response of the composite, effective stress-strain-curves are computed for different load cases and compared to experimental observations. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

For a consequent lightweight design the consideration of the nonlinear macroscopic material behaviour of composites, which is amongst others driven by damage and strain–rate effects on the mesoscale, is required. Therefore, the modelling approach using numerical homogenization techniques based on the simulation of representative volume elements which are modelled by the extended finite element method (X–FEM) is currently extended to nonlinear material behaviour. While the glass fibres are assumed to remain linear elastic, a viscoplastic constitutive law accounts for strain–rate dependence and inelastic deformation of the matrix material. This paper describes the process of finding suitable constitutive relations for the polymeric matrix material Polypropylene in the small–strain regime. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Extended abstract of a paper presented at Microscopy and Microanalysis 2008 in Albuquerque, New Mexico, USA, August 3 – August 7, 2008

The alignment of β-sheets within spider dragline silk fibers is an important factor in their tensile strength and extensibility. We are using linear dichroism of the C 1s → π*amide transition measured using scanning transmission X-ray microscopy (STXM) to generate quantitative maps of the orientation parameters with 30 nm spatial resolution. Here we have extended these measurements from dry samples to samples with partial or full hydration. A device for monitoring and controlling the humidity of a sample in the STXM is described and used to measure the effect of saturated humidity on a section of N. clavipes dragline spider silk. The microstructure and distributions of molecular orientation change considerably with hydration in ways consistent with the supercontraction observed in free standing dragline spider silk. The STXM results are compared to infrared and Raman microscopy results.

Three dimensional (3-d) chemical mapping using angle scan tomography in a soft X-ray scanning transmission X-ray microscope (STXM) has been applied to quantitative chemical mapping in three dimensions of calcium carbonate biomineralization by planktonic freshwater cyanobacteria of the strain Synechococcus leopoliensis PCC 7942. Aspects of making and mounting grid sections, acquiring multi-energy, multi-angle sequences, and data analysis are discussed.

International audience; We haveinvestigatedthenanotextureandcrystallographicorientationofaragoniteinacoralskeleton using synchrotron-basedscanningtransmissionX-raymicroscopy(STXM)andtransmissionelectron microscopy(TEM).Polarization-dependentSTXMimagingat40-nmspatialresolutionwasusedto obtain anorientationmapofthe c-axis ofaragoniteonafocusedionbeammilledultrathinsectionofa Porites coral. Thisimagingshowedthatoneofthebasicunitsofcoralskeletons,referredtoasthecenter of calcification(COC),consistsofaclusterof100-nmaragoniteglobulescrystallographicallyaligned over severalmicrometerswithafan-likedistributionandwiththepropertiesofsinglecrystalsatthe mesoscale.Theremainderoftheskeletonconsistsofaragonitesingle-crystalfibersincrystallographic continuitywiththenanoglobulescomprisingtheCOC.Ourobservationprovidesinformationonthe nm-scaleprocessesthatledtobiomineralformationinthissample.Importantly,thepresentstudy illustrateshowthemethodologydescribedhere,whichcombinesHRTEMandpolarization-dependent synchrotron-basedSTXMimaging,offersaninterestingnewapproachforinvestigatingbiomineralizing systems atthenm-scale.