Role of lipid membrane-nucleic acid interactions, DNA-membrane contacts and metal (II) cations in origination of initial cells and in evolution of prokaryotes to eukaryotes.

The problems of the origin of primary cells and eukaryotic cells are discussed in terms of possible role of interactions between nucleic acids with lipid membrane according to corresponding original hypothesis. We propose that there are two main hypotheses of the origin of primary cells: (a). RNA appeared before proteins and DNA [Nature 213 (1967) 119]; (b). it is needed for the appearance of a primary cell, the volume closed by the lipid membrane. There was no information about the ways on how RNA appeared inside that volume for saving the reaction products around. Our hypothesis suggests that one of the starting points in the origination of primary cells was the interaction of nucleic acid and lipid membrane bubbles in the presence of metal (II) ions (which existed in high concentrations in prebiotic conditions), and this resulted in the enclosing of the pro-RNAs inside the lipid membrane. This hypothesis is formulated by us on the basis of experimental biochemical and biophysical studies of the DNA/RNA-phospholipid vesicles interactions in the presence of metal ions (II) fulfilled in the Institute of Biomedical Chemistry, RAMS, Moscow and Institute of Biophysics, RAS, Pushchino. Our belief is that DNA-membrane contacts (DNA-MCs) played an important role in the prokaryotes-to-eukaryotes transition. The model of the confluence of four prokaryotic cells may explain the prokaryotes-to-eukaryotes transition by the way of eukaryotic nuclear pore formation from prokaryotic Bayer' contacts. The main requirement for the following fusion of prokaryotic cells must be their mutual orientation. After possible association, the division of the formed cell is begun. The great advantage of the model of four prokaryotic cells is the profit in the metabolism and the possibility of the intensive growth of intercellular membrane structures.

[Characteristics of Pseudomonas aurantiaca DNA supramolecular complexes at various developmental stages].

Differences in viscoelasticity (eta) and molecular mass (M) values, as well as in the fatty acid profile of lipids in DNA supramolecular complexes (SC) isolated from Pseudomonas aurantiaca cultures at the exponential and stationary growth phases were established for the first time. Typical characteristics of DNA SC from actively growing cells were the following: eta = 315 +/- 15 dl/g, M(DNA) = 39 x 10(6) Da, C16:0 > C18:0 > C18:1 present as basic fatty acids (FA) in a pool of loosely DNA-bound lipids; the tightly DNA-bound lipid fraction consisted of only two acids C18:0 > C16:0. Significantly higher values of viscoelasticity eta = 779 +/- 8 dl/g and M(DNA) = 198 x 10(6) Da were observed for DNA SC of the stationary phase cells; one more FA, C14:0, was detected in the loosely bound lipid fraction, while lipids tightly bound to DNA contained mainly C16:0 > C18:1 > > C18:0 > C14:0 FA. The content of saturated FA in the DNA-bound lipids in the stationary phase cells was twice as high as in the exponential phase cells. The fraction of tightly bound lipids from the stationary phase cells contained nine times more unsaturated fatty acids than the fraction from proliferating cells. These differences in FA composition of DNA-bound lipids demonstrate the importance of lipids for the structural organization and functioning of genomic DNA during bacterial culture development.

[Effect of alkylhydroxybenzenes, microbial anabiosis inducers, on the structural organization of Pseudomonas aurantiaca DNA and on phenotypic dissociation induction].

We revealed a relationship between alkylhydroxybenzene (AHB)-induced changes in the structural organization of supramolecular complexes (SC) of the DNA of Pseudomonas auraniaca and the phenotypic dissociation of this bacterium. The addition of 0.1-0.3 mM hexylresorcinol (C6-AHB), a chemical analogue of microbial anabiosis autoinducers, caused the formation of cystlike refractile cells (CRC) in these gram-negative, nonsporulating bacteria. Inoculating pseudomonad CRC on solid nutrient media resulted in phenotypic dissociation of the microbial population that yielded several variants with different colony structure and morphology. This manifested itself in the conversion of the original S-colony-forming phenotype into the R form and in the formation of less pigmented colonies. These transitions were possibly linked to AHB-induced structural changes in the DNA. In vitro studies revealed that AHB could interact with DNA SC, resulting in their structural modification that manifested itself in changes in their elastoviscosity. DNA supramolecular complexes isolated from proliferating, stationary-phase, and anabiotic P. aurantiaca cells differed in their elastoviscosity and capacity to interact with AHB homologues with different hydrophobicity, such as hexylresorcinol and methylresorcinol (C1-AHB). The DNA SC from actively proliferating cells were characterized by smaller elastoviscosity compared with those from stationary-phase and anabiotic cells, due to the difference in the DNA superspiralization degree and the physiological age of the bacteria involved. C6-AHB produced a pronounced relaxing effect on the DNA SC from exponential-phase P. aurantiaca cells. The less hydrophobic C1-AHB produced a similar effect on the DNA SC from stationary-phase cells. The curve of the dose-effect dependence of C6-AHB had a breaking point within the submillimolar (10(-4) M) concentration range. These concentrations induce the formation of cystlike anabiotic pseudomonad cells that are characterized by an unstable genotype and dissociate into distinct variants upon inoculation on solid media.