Quantitative linear dichroism imaging of molecular processes in living cells made simple by open software tools.

Fluorescence-detected linear dichroism microscopy allows observing various molecular processes in living cells, as well as obtaining quantitative information on orientation of fluorescent molecules associated with cellular features. Such information can provide insights into protein structure, aid in development of genetically encoded probes, and allow determinations of lipid membrane properties. However, quantitating and interpreting linear dichroism in biological systems has been laborious and unreliable. Here we present a set of open source ImageJ-based software tools that allow fast and easy linear dichroism visualization and quantitation, as well as extraction of quantitative information on molecular orientations, even in living systems. The tools were tested on model synthetic lipid vesicles and applied to a variety of biological systems, including observations of conformational changes during G-protein signaling in living cells, using fluorescent proteins. Our results show that our tools and model systems are applicable to a wide range of molecules and polarization-resolved microscopy techniques, and represent a significant step towards making polarization microscopy a mainstream tool of biological imaging.

Upgraded silicon nanowires by metal-assisted etching of metallurgical silicon: a new route to nanostructured solar-grade silicon.

Through metal-assisted chemical etching (MaCE), superior purification of dirty Si is observed, from 99.74 to 99.9884% for metallurgical Si and from 99.999772 to 99.999899% for upgraded metallurgical Si. In addition, large area of silicon nanowires (SiNW) are fabricated. The purification effect induces a ∼35% increase in photocurrent for SiNW based photoelectrochemical cell.

Atypical transcriptional regulation and role of a new toxin-antitoxin-like module and its effect on the lipid composition of Bradyrhizobium japonicum.

A toxin-antitoxin (TA)-like system (designated as bat/bto genes) was identified in Bradyrhizobium japonicum, based on sequence homology and similarities in organization and size to known TA systems. Deletion of the bat/bto module resulted in pleiotropic alterations in cell morphology and metabolism. The generation time of the mutant was considerably decreased in rich media. Atomic force microscopy revealed the modified shape (shorter and wider) and softness of mutant cells. The synthesis of phosphatidylcholine was completely blocked in the mutant bacteria, and vaccenic acid, the predominant fatty acid of membranes of the wild-type cell, was replaced by palmitic acid in the mutant membranes. The mutant bacteria synthesized incomplete lipopolysaccharide molecules. Remarkable changes in the membrane lipid composition may explain the observed morphological alterations and growth properties of the mutant bacteria. The overlapping promoter region of bat/bto and glpD (coding for the aerobic sn-glycerol-3-phosphate dehydrogenase) genes suggests a complex regulation and the involvement of bat/bto in the control of main metabolic pathways and an important role in the maintenance of a normal physiological state of B. japonicum. These data reveal new aspects of the role of TA systems in bacteria.

Nondestructive mechanical release of ordered polymer microfiber arrays from porous templates.

The fabrication of one-dimensional (1D) nanostructures and microstructures inside the pores of porous templates is intensively investigated. The release of these structures is commonly accomplished by etching and destroying the templates. The 1D nanostructures and microstructures tend to condense because of the occurrence of capillary forces during drying of the specimens. It is shown that highly ordered arrays of polymer microfibers can be easily detached from silanized porous templates by mechanical lift-off. This procedure leaves the templates intact, thus allowing their recycling, and does not involve the use of solutions or solvents, thus circumventing condensation. Therefore, mechanical lift-off may enable the up-scaling of template-based approaches to the fabrication of highly ordered assemblies of 1D nanostructures and microstructures.

The ntrPR operon of Sinorhizobium meliloti is organized and functions as a toxin-antitoxin module.

The chromosomal ntrPR operon of Sinorhizobium meliloti encodes a protein pair that forms a toxin-antitoxin (TA) module, the first characterized functional TA system in Rhizobiaceae. Similarly to other bacterial TA systems, the toxin gene ntrR is preceded by and partially overlaps with the antitoxin gene ntrP. Based on protein homologies, the ntrPR operon belongs to the vapBC family of TA systems. The operon is negatively autoregulated by the NtrPNtrR complex. Promoter binding by NtrP is weak; stable complex formation also requires the presence of NtrR. The N-terminal part of NtrP is responsible for the interaction with promoter DNA, whereas the C-terminal part is required for protein-protein interactions. In the promoter region, a direct repeat sequence was identified as the binding site of the NtrPNtrR complex. NtrR expression resulted in the inhibition of cell growth and colony formation; this effect was counteracted by the presence of the antitoxin NtrP. These results and our earlier observations demonstrating a less effective downregulation of a wide range of symbiotic and metabolic functions in the ntrR mutant under microoxic conditions and an increased symbiotic efficiency with the host plant alfalfa suggest that the ntrPR module contributes to adjusting metabolic levels under symbiosis and other stressful conditions.