V. V. Sorokin

A New Type of Magnet-sensitive Inclusions in Cells of Photosynthetic Purple Bacteria

Summary The magnet-sensitive inclusions of a new type were discovered in cells of Rhodopseudomonas and Ectothiorhodospira species. The inclusions formed thread of beads along the main axis of cells and provided a movement of the biomass to the next pole of an applied static magnet. The electron microscopy of ultrathin sections showed a heterogeneous structure of the inclusions. The magnet-sensitive inclusions were the spherical particles containing an electron-transparent core surrounded with electron-dense matrix. The matrix was separated from cytoplasm with a homogeneous envelope of low electron density. X-ray microanalysis demonstrated that the matrix was enriched with iron.

Comparative Study of the Elemental Composition of Vegetative and Resting Microbial Cells

X-ray microanalysis showed that vegetative cells, viable resting forms, and nonviable forms (micromummies) of the bacteria Bacillus cereus and Micrococcus luteus and the yeast Saccharomyces cerevisiae differ in the content of elements S, P, Ca, and K and Ca/K and P/S ratios. Viable resting forms (cystlike refractive cells and bacillar endospores) had more calcium and less phosphorus and potassium than vegetative cells, the difference being higher for bacilli than for micrococci and yeasts. The distinctive feature of all viable resting microbial forms was their low P/S ratios and high Ca/K ratios. The differences revealed in the cellular content and ratios of elements probably reflect changes in ionic homeostasis accompanying the transition of vegetative microbial cells to the dormant state. Relevant potassium parameters indicate that the membranes of viable resting forms retain their barrier function. At the same time, the nonviable micromummies, even those morphologically intact, of B. cereus and S. cerevisiae exhibited an anomalously low content of potassium, while those of M. luteus had an anomalously high content of this element. This suggests that the cellular membranes of micromummies lose their barrier function, which results in a free diffusion of potassium ions across the membranes. The possibility of using the elemental composition parameters for the quick analysis of the physiological state of microorganisms in natural environments is discussed.

[Detection of microorganisms in the environment and the preliminary appraisal of their physiological state by X-ray microanalysis].

The paper deals with the X-ray microanalysis of the elemental composition of bacteriomorphic particles in 170 000-year-old Antarctic permafrost sediments and in indoor dust. A comparative analysis of the phosphorus, sulfur, calcium, and potassium contents and the Ca/K and P/S ratios in these particles and in reference microbial cells occurring in different physiological states showed that the absence of P and/or S peaks in the X-ray spectrum of an object may indicate that it is abiotic. Resting microbial forms can be revealed on the basis of the following characteristic features: an increased content of Ca, a high Ca/K ratio, and a low P/S ratio. Model experiments with nonviable bacterial and yeast micromummies with alterations in the structural and barrier functions of the cytoplasmic membrane showed that micromummies can be recognized by a superhigh content of a marker element (e.g., P, K, or Si), accumulated due to facilitated diffusion along a deliberately created concentration gradient. Such an analysis of the permafrost sediment and dust made it possible to suggest the presence of mummified cells in these objects. The possibility of using X-ray microanalysis for the detection of microbial cells in natural habitats in order to enhance the efficiency of ecological monitoring of the environment is discussed.

Biosorption of Rare Earth Elements

Abstract By using X-ray microanalysis, the mechanism of sorption of rare earth elements (REE) and their localization in cells of Candida utilis were found to depend on the metal ion speciation in solution, the permeability of the cytoplasmic membrane (CPM), and elemental composition of cells. Sorption capacity of the yeast cells increased with the increase in the pH of solution, which is connected with the extent of metal hydrolysis. Cells with native permeability of CPM did not sorb either scandium at pH values below 4.5 or lanthanum and samarium at pH values below 5.0. Such cells accumulate rare earth elements on surface structures. Only the cells with impaired CPM could sorb REE from the acid solutions. In this case, REE were accumulated inside the cells due to the interaction with phosphorus-containing compounds; the amount of sorbed REE depended on the content of phosphorus in the yeast cells. The yeast cells were shown to have extremely high affinity to scandium which thus can be selectively sorbed ...

Synthesis of magneto-sensitive iron-containing nanoparticles by yeasts

Abstract Industrial production of magneto-sensitive nanoparticles, which can be used in the production of target drug delivery carriers, is a subject of interest for biotechnology and microbiology. Synthesis of these nanoparticles by microorganisms has been described only for bacterial species. At the same time, it is well known that yeasts can form various metal-containing nanoparticles used, for instance, in semiconductors, etc. This paper describes the first results of the biosynthesis of magneto-sensitive nanoparticles by yeasts. The organisms we used—Saccharomyces cerevisiae and Cryptococcus humicola—represented two different genera. Magneto-sensitive nanoparticles were synthesized at room temperature in bench-scale experiments. The study included transmission electron microscopy of the yeast cells and their energy dispersive spectrum analyses and revealed the presence of iron-containing nanoparticles. Both yeast cultures synthesized nanoparticles at high concentrations of dissolved iron. Electron microscopy showed that nanoparticles were associated mainly with the yeast cell wall. Formation of magneto-sensitive nanoparticles was studied under conditions of applied magnetic fields; a possible stimulating role of magnetic field is suggested. On the whole, the paper reports a novel approach to green biosynthesis of magneto-sensitive nanoparticles.

[Accumulation of inorganic polyphosphates in Saccharomyces cerevisiae under nitrogen deprivation: Stimulation by magnesium ions and peculiarities of localization].

The yeast Saccharomyces cerevisiae was shown to have a high potential as a phosphate-accumulating organism under growth suppression by nitrogen limitation. The cells took up over 40% of phosphate from the medium containing 30 mM glucose and 5 mM potassium phosphate and over 80% of phosphate on addition of 5 mM magnesium sulfate. The major part of accumulated Pi was reserved as polyphosphates. The content of polyphosphates was ∼57 and ∼75% of the phosphate accumulated by the cells in the absence and presence of magnesium ions, respectively. The content of long-chain polyphosphates increased in the presence of magnesium ions, 5-fold for polymers with the average length of ∼45 phosphate residues, 3.7-fold for polymers with the average chain length of ∼75 residues, and more than 10-fold for polymers with the average chain length of ∼200 residues. On the contrary, the content of polyphosphates with the average chain length of ∼15 phosphate residues decreased threefold. According to the data of electron and confocal microscopy and X-ray microanalysis, the accumulated polyphosphates were localized in the cytoplasm and vacuoles. The cytoplasm of the cells accumulating polyphosphates in the presence of magnesium ions had numerous small phosphorus-containing inclusions; some of them were associated with large electron-transparent inclusions and the cytoplasmic membrane.

Characterization of technetium(vII) reduction by cell suspensions of thermophilic bacteria and archaea

Washed cell suspensions of the anaerobic hyperthermophilic archaea Thermococcus pacificus and Thermoproteus uzoniensis and the anaerobic thermophilic gram-positive bacteria Thermoterrabacterium ferrireducens and Tepidibacter thalassicus reduced technetium [99Tc(VII)], supplied as soluble pertechnetate with molecular hydrogen as an electron donor, forming highly insoluble Tc(IV)-containing grayish-black precipitate. Apart from molecular hydrogen, T. ferrireducens reduced Tc(VII) with lactate, glycerol, and yeast extract as electron donors, and T. thalassicus reduced it with peptone. Scanning electron microscopy and X-ray microanalysis of cell suspensions of T. ferrireducens showed the presence of Tc-containing particles attached to the surfaces of non-lysed cells. This is the first report on the reduction in Tc(VII) by thermophilic microorganisms of the domain Bacteria and by archaea of the phylum Euryarchaeota.

Functions of non-crystal magnetosomes in bacteria

Intracellular non-crystal magnetosomes are presented in prokaryotes of different taxonomic and physiological groups. Formation of the internal magnetosomes is provoked with some external agents. The situation permits to discuss functions of the magnetosomes as responses to surroundings. A few possible functions are discussed. Hypothesis on oriented motion of bacteria in geomagnetic field suits well data on the linear intracellular distribution of the magnetosomes in some species. An additional hypothesis is oriented attraction of iron-containing compounds to magnetic bacteria. Independently, magnetosomes have a function of the intracellular iron storage. In strong magnetic field, magnetosomes stimulated lysis of bacteria. Sometimes the bacterial lysis was accompanied with production of nanocells.

Pyroelectric effect in ultrathin layers of achiral mesogenic composites

The pyroelectric properties of the solid mixtures of achiral liquid crystalline polymers with their monomers were studied. The composites were fabricated in a thin film form (less than 1 μm) by spin-coating technique. The maximum value of the current responsivity being 0.67 μA/W has been obtained for optimum monomer/polymer ratio of 33%:67% by weight. The pyroelectric voltage was measured in the frequency range from 10 Hz up to 250 kHz. The figure of merit for the composite at room temperature is about 0.8 nC/cm2 K, which is more than twice higher than that of polyvinylidene fluoride with trifluroethylene 70%:30%.

[Surviving Forms in Antibiotic-Treated Pseudomonas aeruginosa].

Survival of bacterial populations treated with lethal doses of antibiotics is ensured by very small numbers of persister cells. Unlike antibiotic-resistant cells, antibiotic tolerance of persisters is not inheritable and reversible. The present work provides evidence supporting the hypothesis on transformation (maturation) of persisters of an opportunistic pathogen Pseudomonas aeruginosa, revealed by ciprofloxacin (CF) treatment (25–100 μg/mL), into dormant cystlike cells (CLC) and nonculturable cells (NC), as was described previously for a number of non-spore-forming bacteria. Subpopulations of type 1 and type 2 persisters, which survived antibiotic treatment and developed into dormant forms, were heterogeneous in their capacity to form colonies or microcolonies upon germination as resistance to heating at 70°C and in cell morphology. Type 1 persisters, which were formed after 1-month incubation of the stationary-phase cultures grown in the medium with decreased C and N concentrations, developed in several types of surviving cells, including those similar to CLC in cell morphology. In the course of 1-month incubation of type 2 persisters, which were formed in exponentially growing cultures, other types of surviving cells developed: immature CLC and L-forms. Unlike P. aeruginosa CLC formed in the control post-stationary phase cultures without antibiotic treatment, most of 1-month persisters, especially type 2 ones, were characterized by the loss of colony-forming capacity, probably due to transition into an nonculturable state with relatively high numbers of live intact cells (Live/Dead test). Another survival strategy of P. aeruginosa populations was ensured by a minor subpopulation of CF-tolerant and CF-resistant cells able to grow in the form of microcolonies or regular colonies of decreased size in the presence of the antibiotic. The described P. aeruginosa dormant forms may be responsible for persistent forms in bacteria carriers and latent infections and, together with antibiotic-resistant cells, are important as components of test systems to assay the efficiency of potential pharmaceuticals against resistant infections.