Characterization of an antifungal glycolipid secreted by the yeast Sympodiomycopsis paphiopedili

An antifungal glycolipid was purified from the culture liquid of the ustilaginomycetous yeast Sympodiomycopsis paphiopedili by column and thin-layer chromatography. According to nuclear magnetic resonance and mass-spectroscopy experiments it was a cellobioside containing 2,15,16-trihydroxypalmitic acid as an aglycon. The minimal effective concentrations leading to ATP leakage and growth inhibition were 45 and 160 microg ml(-1) for Cryptococcus terreus and Candida albicans, respectively.     

An in silico investigation into the causes of telomere length heterogeneity and its implications for the Hayflick limit

In telomerase-negative cell populations the mean telomere length (TL) decreases with increasing population doubling number (PD). A critically small TL is believed to stop cell proliferation at a cell-, age- and species-specific PD thus defining the Hayflick limit. However, positively skewed TL distributions are broad compared to differences between initial and final mean TL and strongly overlap at middle and late PD, which is inconsistent with a limiting role of TL. We used computer-assisted modelling to define what set of premises may account for the above. Our model incorporates the following concepts. DNA end replication problem: telomeres loose 1 shortening unit (SU) upon each cell division. Free radical-caused TL decrease: telomeres experience random events resulting in the loss of a random SU number within a remaining TL. Stochasticity of gene expression and cell differentiation: cells experience random events inducing mitoses or committing cells to proliferation arrest, the latter option requiring a specified number of mitoses to be passed. Cells whose TL reaches 1SU cannot divide. The proliferation kinetics of such virtual cells conforms to the transition probability model of cell cycle. When no committing events occur and at realistic SU estimates of the initial TL, maximal PD values far exceed the Hayflick limit observed in normal cells and are consistent with the crisis stage entered by transformed cells that have surpassed the Hayflick limit. At intermediate PD, symmetrical TL distributions are yielded. Upon introduction of committing events making the ratio of the rates of proliferating and committing events (P/C) range from 1.10 to 1.25, TL distributions at intermediate PD become positively skewed, and virtual cell clones show bimodal size distributions. At P/C as high as 1.25 the majority of virtual cells at maximal PD contain telomeres with TL>1SU. A 10% increase in P/C within the 1.10-1.25 range produces a two-fold increase in the maximal PD, which can reach values of up to 25 observed in rodent and some human cells. Increasing the number of committed mitoses from 0 to 10 can increases PD to about 50 observed in human fibroblasts. Introduction of the random TL breakage makes the shapes of TL distributions quite dissimilar from those observed in real cells. CONCLUSIONS: Telomere length decrease is a correlate of cell proliferation that cannot alone account for the Hayflick limit, which primarily depends on parameters of cell population kinetics. Free radical damage influences the Hayflick limit not through TL but rather by affecting the ratio of the rates of events that commit cells to mitoses or to proliferation arrest.     

Mycocinogeny in smut yeast-like fungi of the genus <Emphasis Type="Italic">Pseudozyma</Emphasis>

The fungistatic agent secreted by Pseudozyma prolifica VKM Y-2835 shows activity against some representatives of the Ustilaginales under acidic conditions. This mycocin, with a molecular mass of no less than 15 kDa, is thermolabile and sensitive to proteolytic cleavage.     

Laboratory modeling of nonstationary processes in space cyclotron masers: First results and prospects

Results are presented from laboratory modeling of the dynamics of space cyclotron masers. A selfoscillatory mode of cyclotron instability in the nonequilibrium plasma of an ECR discharge in a magnetic mirror trap is found. The plasma comprises two electron populations: the background population with a density of N _e ～ 10¹³–10¹⁴ cm^?3 and temperature of T _e ≈ 300 eV and the energetic population with a density of N _e ～ 10¹⁰ cm^?3 and temperature of T _e ≈ 10 keV. Quasi-periodic pulsed precipitation of energetic electrons from the trap, accompanied by microwave bursts at frequencies below the electron gyrofrequency in the center of the trap, is detected. The study of the microwave plasma emission and the energetic electrons precipitated from the trap shows that the precipitation is related to the excitation of whistler-mode waves propagating nearly parallel to the trap axis. The observed instability has much in common with phenomena in space magnetic traps, such as radiation belts of magnetized planets and solar coronal loops. The experimental results demonstrate the opportunity of laboratory modeling of space cyclotron masers. The main tasks and possibilities of such modeling are discussed.     

Antifungal cellobiose lipid secreted by the epiphytic yeast <Emphasis Type="Italic">Pseudozyma graminicola</Emphasis>

The yeast Pseudozyma graminicola isolated from plants inhibited growth of almost all ascomycetes and basidiomycetes tested (over 270 species of ca. 100 genera) including pathogenic species. This yeast secreted a fungicidal agent, which was identified as a glycolipid composed of cellobiose residue with two O-substituents (acetyl and 3-hydroxycaproic acid) and 2,15,16-trihydroxypalmitic acid. The release of ATP from the glycolipid-treated cells indicated that this glycolipid impaired the permeability of the cytoplasmic membrane. Basidiomycetes were more sensitive to the cellobiose lipid than ascomycetes.     

Myo-inositol assimilating new species of Rhodotorula Harrison

A new species of anamorphic basidiomycetous yeasts, Rhodotorula pinalis, was isolated from needle litter of Pinus sylvestris L. collected in Moscow oblast (Russia). The cultures are nonpigmented; nitrate- and myo-inositol-positive, forming no ballistoconidia.     

Two-dimensional modeling of a transverse collisionless shock wave

Transverse collisionless shock waves in a plasma in which the initial β value is equal to zero for electrons and is small but nonzero for ions are studied in the two-dimensional approximation with allowance for anomalous resistivity. A hybrid model is applied such that the ions are treated in the kinetic approximation and the electrons are described in the hydrodynamic approximation. A collisionless shock wave is generated using a piston with a small two-dimensional perturbation. The ion distribution downstream of the shock front and the effect of electron and ion heating are analyzed. It is shown that, for Alfvén-Mach numbers M _A>2, ion heating is attributed primarily to the ions that have experienced a reflection from the shock front and whose velocities downstream of the front are very high. This conclusion agrees with the results of one-dimensional calculations. Solving the problem as formulated shows that two-dimensional effects are insignificant in the range of low Alfvén-Mach numbers (M _A≤5): the direction of the magnetic field is always close to its initial direction, the ions acquire low velocities along the magnetic field, and the quantitative parameters of the plasma downstream of the shock front are close to those obtained from the one-dimensional model. In the range of higher Alfvén-Mach numbers, two-dimensional effects are more pronounced and the ion distribution function is less anisotropic.     

Characteristics of transposition of Tn7-like elements determining resistance to trimethoprim and streptomycin

The transposing elements Tn7, Tn1824, controlling the resistance to trimethoprim and Tn1925, Tn1826, carrying the streptothricin resistance genes were classified as a new transposon family on the basis of their physical structure. The comparative genetic analysis of the frequency, specificity and insertion orientation in different replicons, obtained in independent research systems in this study, demonstrated the identity of transposition characteristics of the transposons. The latter makes it possible to classify them as an independent transposon family. The peculiar feature of the Tn7-like elements family is their RecA-dependent transposition into the chromosome of Escherichia coli stimulated by bacteriophage Plkc transduction of the transposons.     

Selenium tolerance of yeasts

Selenium tolerance of yeasts widely varies: the growth of some yeasts can be inhibited by a selenium concentration as low as 10(-4) M, whereas others can grow in the presence of 10(-1) M selenium. Homogeneous yeast taxa are characterized by a certain level of selenium tolerance, and heterogeneous taxa show a variable level of tolerance to selenium. In general, ascomycetous yeasts are more tolerant to selenium than basidiomycetous yeasts. Among the ascomycetous yeasts, the genera Dekkera and Schizosaccharomyces exhibited the lowest and the species Candida maltosa, Hanseniaspora valbyensis, Kluyveromyces marxianus, and Yarrowia lipolytica the highest tolerance to selenium. Among the basidiomycetous yeasts, the genera Bullera, Cryptococcus, and Holtermannia showed the lowest and the species Cryptococcus curvatus, Cr. humicola, and Trichosporon spp. the highest tolerance to selenium. The selenium tolerance of yeasts depends on the composition of the growth medium, in particular, on the presence of sulfate, sulfur-containing amino acids, and glutamine in the medium.