Olga I. Kiselyova

Comparative studies of bacteria with an atomic force microscopy operating in different modes.

Escherichia coli bacterial cells of two strains JM109 and K12 J62 were imaged with atomic force microscopy (AFM) in different environmental conditions. The AFM results show that the two strains have considerable difference in the surface morphology. At the same time after rehydration both strains show the loss of the topographic features and increase in lateral and vertical dimensions. Results obtained in different AFM modes (contact, tapping, MAC) were compared. Imaging in culture medium was applied for direct observation of the surface degradation effect of lysozyme. The treatment of the cells with the enzyme in the culture medium lead to the loss of surface rigidity and eventually to dramatic changes of the bacteria shape.

Microbial Surfaces Investigated Using Atomic Force Microscopy

This paper is dedicated to atomic force microscopy (AFM) as a progressive tool for imaging bacterial surfaces and probing their properties. The description of the technique is complemented by the explanation of the methodapos;s artifacts typical, in particular, for the imaging of bacterial cells. Sample preparation techniques are summarized in a separate section. Special attention is paid to the differences in imaging of Gram‐positive and Gram‐negative bacteria. Probing of mechanical properties, including elastic modulus, fragility, and adhesion of the cell walls is emphasized. The advantages of AFM in the studies of real‐time cellular dynamical processes are illustrated by the experiment with the germination of spores.

Regulation of RNA Translation in Potato Virus X RNA-Coat Protein Complexes: The Key Role of the N-Terminal Segment of the Protein

The efficiency of in vitro translation of the potato virus X (PVX) RNA was studied for viral ribonucleoprotein complexes (vRNP) assembled from the genomic RNA and the viral coat protein (CP). In vRNP particles the 5′-proximal RNA segments were encapsidated into the CP, which formed helical headlike structures differing in length. Translation of the PVX RNA was completely suppressed upon incubation with PVX CP and was activated within vRNPs assembled in vitro with two CP forms, differing in the modification of the N-terminal peptide containing the main phosphorylation site(s) for Thr/Ser protein kinases. It was shown that CP phosphorylation activates RNA translation within vRNPs and that the removal of the N-terminal peptide of CP suppresses activation, but CP still acts as a translational suppressor. This fact made it possible to suppose that the replacement of Ser/Thr by amino acid residues that are not subject to phosphorylation in the N-terminal peptide of CP of the mutant PVX (PVX-ST) completely inhibits RNA translation within vRNP. However, experiments disproved this assumption: PVX-ST RNA was efficiently translated within native virions, RNA of the wild-type (wt) PVX was efficiently translated in heterogeneous vRNP (wtRNA + PVX-ST CP), and the opposite result (repression of translation) was obtained for another heterogeneous vRNP (PVX-ST RNA + wtCP). Therefore, the N-terminal CP peptide located on the surface of the PVX virion or vRNP particles plays a key role in the activation of viral RNA translation.

Scanning Probe Microscopy Of Biomacromolecules: Nucleic Acids, Proteins And Their Complexes

After successful imaging of DNA biomacromolecules using scanning probe microscopy (SPM) (Bustamante et al., 1992) much progress was achieved in the visualization of their different morphological features in air and liquid environments: cruciforms, R-loops, etc. SPM gives an opportunity for real-time studies of conformational changes of DNA molecules induced by chemical reagents - formation of torroidal and rod-like structures. Recently, SPM has greatly assisted in the measurements of electrical conductivity of individual DNA molecules (Kasumov et al., 2001). SPM opens new possibilities in the study of single macromolecule micromechanics: rigidity, strength of chemical bond and adhesion.

Chitosan coatings with enhanced biostability in vivo

In this article, we study the stability of chitosan coatings applied on glutaraldehyde-stabilized bovine pericardium when exposed to biodegradation in vivo in the course of model subcutaneous tests on rats. The coatings were deposited from carbonic acid solutions, that is, H2 O saturated with CO2 at high pressure. Histological sections of treated pericardium samples demonstrated that the structure of pericardial connective tissues was not significantly altered by the coating application method. It was revealed that the dynamics of biodegradation depended on the total mass of chitosan applied as well as on the DDA of chitosan used. As long as the amount of chitosan did not exceed a certain threshold limit, no detectable degradation occurred within the time of the tests (12 weeks for the rat model). For higher chitosan amounts, we detected a ∼20% reduction of the mass after the in vivo exposition. The presumed mechanism of such behavior is discussed.