The multiple faces of self-assembled lipidic systems

Lipids, the building blocks of cells, common to every living organisms, have the propensity to self-assemble into well-defined structures over short and long-range spatial scales. The driving forces have their roots mainly in the hydrophobic effect and electrostatic interactions. Membranes in lamellar phase are ubiquitous in cellular compartments and can phase-separate upon mixing lipids in different liquid-crystalline states. Hexagonal phases and especially cubic phases can be synthesized and observed in vivo as well. Membrane often closes up into a vesicle whose shape is determined by the interplay of curvature, area difference elasticity and line tension energies, and can adopt the form of a sphere, a tube, a prolate, a starfish and many more. Complexes made of lipids and polyelectrolytes or inorganic materials exhibit a rich diversity of structural morphologies due to additional interactions which become increasingly hard to track without the aid of suitable computer models. From the plasma membrane of archaebacteria to gene delivery, self-assembled lipidic systems have left their mark in cell biology and nanobiotechnology; however, the underlying physics is yet to be fully unraveled

From dispersed nanodiscs to thin films of layered organic material via reversible swelling

We show that nanodiscs stabilized with polymers order and pile up on a surface upon drying. The resulting surface films with an average thickness of one micron are made of collapsed cohesive layers with smectic long-range order. This occurs with and without plastifying stabilizing polymer and produces crevasses. The stacked discs undergo a two-to-three-dimensional crystallization while bottom layers close to the surface fuse and produce infinite bilayers. Small angle X-ray scattering experiments demonstrate that excess polymer is segregated from the crystalline stack. Water adsorption isotherms show that reversible swelling of the excess polymer does not destroy the compact stack of partially fused nanodiscs collapsed parallel to the surface. In the absence of chemical binding, the stacks of layered nanodiscs can be removed by simple washing with pure water. AFM, TEM and SEM experiments demonstrate that presence of crevasses is quenched by the presence of a plastifying polymer.© Elsevie

DNA- and RNA-based stable isotope probing of hydrocarbon degraders.

The microbial degradation of hydrocarbons in contaminated environments can be driven by distinct aerobic and anaerobic populations. While the physiology and biochemistry of selected degraders isolated in pure culture have been intensively studied in recent decades, research has now started to take the generated knowledge back to the field, in order to identify microbes truly responsible for degradation in situ. Partially, this has been facilitated by stable isotope probing (SIP) of nucleic acids. This chapter discusses the concepts and important methodological foundations of SIP and provides a detailed workflow for the application of DNA- and rRNA-based SIP to degraders of petroleum hydrocarbons in aerobic and anaerobic systems. SIP is capable of providing direct knowledge on intrinsic hydrocarbon degrader populations in diverse environmental and technical systems, which is an important step toward more integrated concepts in contaminated site monitoring and bioremediation