Horizontal Transfer of Virulence Factors by Pathogenic Enterobacteria to Marine Saprotrophic Bacteria during Co-Cultivation in Biofilm.

Environmental problems associated with marine pollution and climate warming create favorable conditions for the penetration and survival of pathogenic bacteria in marine ecosystems. These microorganisms have interspecific competitive interactions with marine bacteria. Co-culture, as an important research strategy that mimics the natural environment of bacteria, can activate silent genes or clusters through interspecies interactions. The authors used modern biotechnology of co-cultivation to dynamically study intercellular interactions between different taxa of bacteria-pathogenic enterobacteria Yersinia pseudotuberculosis and Listeria monocytogenes and saprotrophic marine bacteria Bacillus sp. and Pseudomonas japonica isolated in summer from the coastal waters of the recreational areas of the Sea of Japan. The results of the experiments showed that during the formation of polycultural biofilms, horizontal transfer of genes encoding some pathogenicity factors from Y. pseudotuberculosis and L. monocytogenes to marine saprotrophic bacteria with different secretion systems is possible. It was previously thought that this was largely prevented by the type VI secretion system (T6SS) found in marine saprotrophic bacteria. The authors showed for the first time the ability of marine bacteria Bacillus sp. and P. japonica to biofilm formation with pathogenic enterobacteria Y. pseudotuberculosis and L. monocytogenes, saprophytic bacteria with type III secretion system (T3SS). For the first time, a marine saprotrophic strain of Bacillus sp. Revealed manifestations of hyaluronidase, proteolytic and hemolytic activity after cultivation in a polycultural biofilm with listeria. Saprotrophic marine bacteria that have acquired virulence factors from pathogenic enterobacteria, including antibiotic resistance genes, could potentially play a role in altering the biological properties of other members of the marine microbial community. In addition, given the possible interdomain nature of intercellular gene translocation, acquired virulence factors can be transferred to marine unicellular and multicellular eukaryotes. The results obtained contribute to the paradigm of the epidemiological significance and potential danger of anthropogenic pollution of marine ecosystems, which creates serious problems for public health and the development of marine culture as an important area of economic activity in coastal regions.

Glycyrrhizin-Assisted Transport of Praziquantel Anthelmintic Drug through the Lipid Membrane: An Experiment and MD Simulation.

Praziquantel (PZQ) is one of the most widespread anthelmintic drugs. However, the frequent insufficient application of PZQ after oral administration is associated with its low solubility, penetration rate, and bioavailability. In the present study, the permeation of PZQ through a 1,2-dioleoyl- sn-glycero-3-phosphocholine (DOPC) membrane was investigated to probe glycyrrhizin-assisted transport. Glycyrrhizin (or glycyrrhizic acid, GA), a natural saponin, shows the ability to enhance the therapeutic activity of various drugs when it is used as a drug delivery system. However, the molecular mechanism of this effect is still under debate. In the present study, the transport rate was measured experimentally by a parallel artificial membrane permeation assay (PAMPA) and molecular dynamics (MD) simulation with DOPC lipid bilayers. The formation of the noncovalent supramolecular complex of PZQ with disodium salt of GA (Na2GA) in an aqueous solution was proved by the NMR relaxation technique. PAMPA experiments show a strong increase in the amount of the penetrating praziquantel molecules in comparison with a saturated aqueous solution of pure drug used as a control. MD simulation of PZQ penetration through the bilayer demonstrates an increase in permeability into the membrane in the presence of a glycyrrhizin molecule. A decrease in the free energy barrier in the middle of the lipid bilayer was obtained, associated with the hydrogen bond between PZQ and GA. Also, GA reduces the local bilayer surface resistance to penetration of PZQ by rearranging the surface lipid headgroups. This study clarifies the mechanism of increasing the drug's bioavailability in the presence of glycyrrhizin.

Intermolecular Voids in Lipid Bilayers in the Presence of Glycyrrhizic Acid.

It is known that glycyrrhizic acid (GA) promotes the enhancement of the activity of several medicines. This is attributed to the fact that GA increases the membrane permeability of small drug molecules. There is an opinion that GA facilitates the formation of additional large voids in the membrane, which enhance the passive diffusion of molecules across the membrane. In this work, we investigate how GA influences the intermolecular voids using the molecular dynamics simulation. We calculate the interstitial spheres (empty spheres inscribed between molecules) in model DPPC and DOPC bilayers, both pure and with the addition of cholesterol. It was observed that the addition of GA does not lead to the formation of new large interstitial spheres; i.e., new large voids do not appear. The distribution of empty volume inside the bilayers is also studied. We calculated the profiles of the empty volume fraction both from the middle plane of the bilayer and from its outer surface (from the lipid-water interface). This analysis has shown that the addition of GA does not cause the increase of the empty volume in the bilayer; moreover, there is a slight decrease in the bilayers with cholesterol. Thus, we have not found a confirmation of the simplest hypothesis that individual GA molecules induce pores in the membrane.

Calculation of the volumetric characteristics of biomacromolecules in solution by the Voronoi-Delaunay technique.

Recently a simple formalism was proposed for a quantitative analysis of interatomic voids inside a solute molecule and in the surrounding solvent. It is based on the Voronoi-Delaunay tessellation of structures, obtained in molecular simulations: successive Voronoi shells are constructed, starting from the interface between the solute molecule and the solvent, and continuing to the outside (into the solvent) as well as into the interior of the molecule. Similarly, successive Delaunay shells, consisting of Delaunay simplexes, can also be constructed. This technique can be applied to interpret volumetric data, obtained, for example, in studies of proteins in aqueous solution. In particular, it allows replacing qualitatively and descriptively introduced properties by strictly defined quantities, such as the thermal volume, by the boundary voids. The extension and the temperature behavior of the boundary region, its structure and composition are discussed in detail, using the example of a molecular dynamics model of an aqueous solution of the human amyloid polypeptide, hIAPP. We show that the impact of the solute on the local density of the solvent is short ranged, limited to the first Delaunay and the first Voronoi shell around the solute. The extra void volume, created in the boundary region between solute and solvent, determines the magnitude and the temperature dependence of the apparent volume of the solute molecule.