Nanoscale Electric Characteristics and Oriented Assembly of Halobacterium salinarum Membrane Revealed by Electric Force Microscopy

Abstract

Purple membranes (PM) of the bacteria Halobacterium salinarum are a unique natural membrane where bacteriorhodopsin (BR) can convert photon energy and pump protons. Elucidating the electronic properties of biomembranes is critical for revealing biological mechanisms and developing new devices. We report here the electric properties of PMs studied by using multi-functional electric force microscopy (EFM) at the nanoscale. The topography, surface potential, and dielectric capacity of PMs were imaged and quantitatively measured in parallel. Two orientations of PMs were identified by EFM because of its high resolution in differentiating electrical characteristics. The extracellular (EC) sides were more negative than the cytoplasmic (CP) side by 8 mV. The direction of potential difference may facilitate movement of protons across the membrane and thus play important roles in proton pumping. Unlike the side-dependent surface potentials observed in PM, the EFM capacitive response was independent of the side and was measured to be at a dC/dz value of ~5.25 nF/m. Furthermore, by modification of PM with de novo peptides based on peptide-protein interaction, directional oriented PM assembly on silicon substrate was obtained for technical devices. This work develops a new method for studying membrane nanoelectronics and exploring the bioelectric application at the nanoscale.

Halobacterium salinarum NRC-1 Sustains Voltage Production in a Dual-Chambered Closed Microbial Fuel Cell

“…Light energy captured by these purple membrane proteins are converted into structural changes that pump protons across the cytoplasm to the extracellular side. is proton pump creates an electrochemical gradient that helps drive cellular processes within H. salinarum [15][16][17]. Archaeal rhodopsin has been the most important biomolecule extracted from H. salinarum for commercial use in a variety of optometric-related technologies [18] and could be of use in bioanodes.…”