Transmission Electron Microscopy, High Resolution X-Ray Diffraction and Rutherford Backscattering Study of Strain Release in InGaAs/GaAs Buffer Layers

Strain release and dislocation distribution in InGaAs/GaAs double heterostructures, step-graded and linear-graded buffer layers have been studied. A higher misfit dislocation density at the inner interface between the InGaAs layer and the substrate was found in all the samples. This corresponded to a strain release of the inner ternary layers much larger than predicted by equilibrium theories. The residual parallel strain of the external layers as a function of their thickness was found to follow a curve approximately of slope -0.5, in agreement with previous investigations on single InGaAs layers. This result has been interpreted as evidence that the elastic energy per unit interface area remains constant during the epilayer growth. The presence of numerous single and multiple dislocation loops inside the substrate was attributed to the strain relaxation occurring through dislocation multiplication via Frank-Read sources activated during the growth. A comparison with InGaAs/GaAs step-graded and linear-graded heterostructures is also shown and briefly discussed. Finally, lattice plane tilts between epilayers and substrates have been found due to the imbalance in the linear density of misfit dislocations with opposite component of the Burgers vector, b⊥eff, perpendicular to the interface

The Microbiome of Brazilian Mangrove Sediments as Revealed by Metagenomics

Here we embark in a deep metagenomic survey that revealed the taxonomic and potential metabolic pathways aspects of mangrove sediment microbiology. The extraction of DNA from sediment samples and the direct application of pyrosequencing resulted in approximately 215 Mb of data from four distinct mangrove areas (BrMgv01 to 04) in Brazil. The taxonomic approaches applied revealed the dominance of Deltaproteobacteria and Gammaproteobacteria in the samples. Paired statistical analysis showed higher proportions of specific taxonomic groups in each dataset. The metabolic reconstruction indicated the possible occurrence of processes modulated by the prevailing conditions found in mangrove sediments. In terms of carbon cycling, the sequences indicated the prevalence of genes involved in the metabolism of methane, formaldehyde, and carbon dioxide. With respect to the nitrogen cycle, evidence for sequences associated with dissimilatory reduction of nitrate, nitrogen immobilization, and denitrification was detected. Sequences related to the production of adenylsulfate, sulfite, and H2S were relevant to the sulphur cycle. These data indicate that the microbial core involved in methane, nitrogen, and sulphur metabolism consists mainly of Burkholderiaceae, Planctomycetaceae, Rhodobacteraceae, and Desulfobacteraceae. Comparison of our data to datasets from soil and sea samples resulted in the allotment of the mangrove sediments between those samples. The results of this study add valuable data about the composition of microbial communities in mangroves and also shed light on possible transformations promoted by microbial organisms in mangrove sediments

Nestin-GFP Transgene Reveals Neural Precursor Cells in Adult Skeletal Muscle

Background: Therapy for neural lesions or degenerative diseases relies mainly on finding transplantable active precursor cells. Identifying them in peripheral tissues accessible for biopsy, outside the central nervous system, would circumvent the serious immunological and ethical concerns impeding cell therapy. Methodology/Principal Findings: In this study, we isolated neural progenitor cells in cultured adult skeletal muscle from transgenic mice in which nestin regulatory elements control GFP expression. These cells also expressed the early neural marker Tuj1 and light and heavy neurofilament but not S100b, indicating that they express typical neural but not Schwann cell markers. GFP+/Tuj1+ cells were also negative for the endothelial and pericyte markers CD31 and a-smooth muscle actin, respectively. We established their a) functional response to glutamate in patch-clamp recordings; b) interstitial mesenchymal origin; c) replicative capacity; and d) the environment necessary for their survival after fluorescenceactivated cell sorting. Conclusions/Significance: We propose that the decline in nestin-GFP expression in muscle progenitor cells and its persistence in neural precursor cells in muscle cultures provide an invaluable tool for isolating a population of predifferentiated neural cells with therapeutic potential

Understanding the Influence of Adsorption-Mediated Processes on Antibody Aggregation in Bioprocessing

Affinity chromatography is an indispensable method of protein purification used during the manufacture of many therapeutic antibodies. The protein A ligand is a popular choice for selective purification of immunoglobulin G (IgG) molecules. Aggregated product is often found in protein A elution pools; this is generally attributed to the effect of low pH (elution) on protein structure. However, there is evidence that other facets of the chromatography process influence aggregation phenomena. Physical and chemical transitions, such as concentration of protein on the adsorbent surface and change in buffer composition, may challenge the structural integrity of proteins, increasing their propensity for aggregation. The influence of elution from protein A on the aggregation rate of an IgG4 during a subsequent low pH hold was investigated. IgG4 was incubated in elution buffer after protein A chromatography and the monomer concentration in neutralised samples was quantified by size exclusion chromatography. Rate constants for monomer decay over time were determined by fitting exponential decay functions to the data. Similar low pH experiments were implemented in the absence of a chromatography step. The IgG4 demonstrated highly pH-dependent and apparently concentration-independent aggregation behaviour. The findings suggested that aggregation was governed predominantly by a pH-dependent unfolding/ re-folding equilibrium. Elution from protein A was found to increase aggregation rates by half an order of magnitude, while other aspects of the aggregation kinetics appeared un-affected. In order to advance understanding of how adsorption processes might impact antibody stability, neutron reflectivity was used to characterise the structure of adsorbed IgG on model surfaces. In the first model system IgG was adsorbed directly to silica and demonstrated a side-on orientation with high surface contact. A maximum dimension of 60Å in the surface normal direction and high density surface coverage were observed under acidic pH conditions. In the second model system protein A was attached to a silica surface to produce a configuration representative of a glass chromatography resin. Interfacial structure was probed during sequential stages from ligand attachment, through IgG binding and elution. Adsorbed IgG structures extended up to 230Å away from the surface and showed dependence on surface blocking strategies. The data was suggestive of two IgG molecules bound to protein A with a somewhat skewed orientation and close proximity to the silica surface. The findings provide insight into the orientation of adsorbed antibody structures under conditions encountered during chromatographic separations. The outcomes of this work provide a broad scope for future investigations. Based on preliminary work, using neutron measurement techniques to monitor aggregate formation inside glass chromatography resins is suggested as an interesting direction