Prediction of the three-dimensional structure of aflatoxin of Aspergillus flavus by homology modelling

Aflatoxins are polyketide-derived secondary metabolites produced by Aspergillus spp. The toxic effects of aflatoxins have adverse consequences for human health and agricultural economics. The aflR gene, a regulatory gene for aflatoxin biosynthesis, encodes a protein containing a zinc-finger DNA-binding motif. AFLR-Protein three-dimensional model was generated using Robetta server. The modeled AFLR-Protein was further optimization and validation using Rampage. In the simulations, we monitored the backbone atoms and the C-α-helix of the modeled protein. The low RMSD and the simulation time indicate that, as expected, the 3D structural model of AFLR-protein represents a stable folding conformation. This study paves the way for generating computer molecular models for proteins whose crystal structures are not available and which would aid in detailed molecular mechanism of inhibition of aflatoxin.     

Serotonin reuptake blocker fluoxetine suppresses hippocampal theta oscillation in rabbits during EEG

In earlier studies it has been shown that stimulation of the median raphe nucleus (MR) in awake rabbits decreases the expression and frequency of oscillatory theta activity in the septohippocampal system, and the functional blockade of this nucleus evokes the regular and high-frequency theta rhythm. The present work was aimed at elucidation of serotoninergic influence of MR (which also contains cells of other chemical nature) to the septohippocampal system of theta activity. Serotonin reuptake blocker fluoxetine that increases brain serotonin level was applied. Hippocampal electroencephalogram was recorded in awake rabbits. Bilateral intracerebroventricular infusion of fluoxetine hydrochloride (Sigma, St. Louis; 15 micrograms in 5 microliters saline) in all cases reduced the rhythmic theta activity. In 15 of 18 (83.3%) of experiments the decrease in hippocampal theta oscillations was more than 50% of the control level. The theta band of the spectral density histogram decreased in the mean by 56 +/- 5.8% of the control level (from 10 to 93% in different experiments, p < 0.001). The mean latency of these changes was 3.5 +/- 0.11 minutes (2.9-4.1 min), the effect duration was 64 +/- 3.2 min (45.3-90 min). The mean frequency of the theta waves did not change as compared to the baseline and was equal to 5.25 +/- 0.5 Hz (4.5-6.5 Hz). The fluoxetine-induced reduction of the theta rhythm expression in hippocampus is the evidence of its inhibitory control by serotoninergic brain system. It is suggested that the increase of the frequency of hippocampal theta rhythm after the functional blockade of MR observed in our earlier experiments was the result of a release of the septohippocampal system from the influence of nonserotoninergic neurons (via glutamatergic reticular formation) and/or temporary cessation of the MR interaction with noradrenergic, dopaminergic and glutamate/aspartate systems.     

Sensory responses of neurons in the medial septal area to modulation of the theta-activity by alpha2-adrenergic receptor agonist clonidine

It was shown by us earlier that bilateral intracerebroventricular injection of alpha2-adrenoreceptor agonist clonidine produced a dose-dependent effect on theta oscillations in the septohippocampal system of awake rabbits. A relatively low dose of clonidine (0.5 microgram) attenuated and a high dose (5 micrograms) significantly enhanced the rhythmic activity. It was suggested that the effect of the low dose of clonidine is mediated by presynaptic alpha2-adrenoreceptors were as postsynaptic alpha2-adrenoreceptors. In this article sensory neuronal responses in the medial septal area (MS) were analyzed against the background of the theta activity modulation by different clonidine doses. Different effects of the low and high doses of the agonist were revealed. The low dose of clonidine (0.5 microgram in 5 microliters into each lateral ventricle) which produced a decrease in the theta activity resulted in attenuation of excitation and enhancement of inhibition, i.e., the number of activating effects significantly decreased and inhibitory responses were more frequent and distinct. The high dose of clonidine (5 micrograms in 5 microliters) which produced a sharp increase in the theta activity led to a significant decrease in the reactions of the MS cells to sensory stimuli (from 76.8% in the control to 45% under clonidine) independently on the initial reaction character. Persisted excitatory and inhibitory responses became less distinct than the initial ones except single excitatory reactions. The results suggest that alpha2-adrenoreceptors are involved in the control of the sensory reactivity of MS neurons. A sharp decrease in neuronal reactivity during stable rhythmical oscillations developing under the influence of high dose of clonidine confirm the role of the theta rhythm in the septohippocampal system as an active filter in information selection and registration.     

Spore germination and mycelial growth of streptomycetes at different humidity levels

This study is the first to show the ability of streptomycetes to develop at a very low humidity level. All of the streptomycetes studied produced growth at low humidity (aw 0.86 and 0.67). This capacity was most markedly pronounced in Streptomyces odorifer, whose spores were capable of germinating, and mycelial germs increased in length, at the air humidity aw 0.50. The formation of lateral branches (mycelium branching) at this humidity was noted only in single S. odorifer germs and only after 72 h of incubation. Study of streptomycete growth on an agarized medium with different osmotic pressures, created by various glycerol concentrations in the medium, showed that, at aw 0.67, the spores of all the streptomycetes studied germinate, producing mycelial germs but not microcolonies. The ecological significance of mycelial prokaryotes in soil microbial communities that develop and function under conditions of extremely low humidity is discussed.     

Actinomycete growth in conditions of low moisture

Actinomycete communities demonstrated a replacement of the generic composition in time as a function of soil moisture. Representatives of the genera Streptomyces, Micromonospora, Actinomadura, Saccharopolyspora, and Microbispora were repeatedly isolated from soil under different moisture conditions (field capacity, maximum molecular capacity, and maximum adsorption capacity). Representatives of some rare genera (Thermomonospora and Kibdelosporangium) were isolated from soil with low moisture levels inhibiting growth of more hydrophilic actinomycetes and bacteria. Spores of some actinomycetes could grow at low relative air humidity (RH) (50 and 67%). The complete growth cycle of all actinomycetes starting from spore germination to sporulation was observed only at RH of 98%.     

Mapping the amino acid properties of constituent nucleoporins onto the yeast nuclear pore complex

Visualization of molecular structures aids in the understanding of structural and functional roles of biological macromolecules. Macromolecular transport between the cell nucleus and cytoplasm is facilitated by the nuclear pore complex (NPC). The ring structure of the NPC is large and contains several distinct proteins (nucleoporins) which function as a selective gate for the passage of certain molecules into and out of the nucleus. In this note we demonstrate the utility of a python code that allows direct mapping of the physiochemical properties of the constituent nucleoporins on the scaffold of the yeast NPC׳s cytoplasmic view. We expect this tool to be useful for researchers to visualize the NPC based on their physiochemical properties and how it alters when specific mutations are introduced in one or more of the nucleoporins. The code developed using Python is available freely from the authors.     

Dynamics of spore germination and mycelial growth of streptomycetes under low humidity conditions

At extremely low values of moisture pressure (?96.4 MPa; a_w 0.50), the spores of xerotolerant streptomycetes (Streptomyces odorifer and S. rubiginosohelvolus) germinated, their germ lengths increased, and lateral branching of the mycelium was observed after 5 days of incubation in a thin layer of agarized nutrient medium. At ?22.6 MPa (a_w 0.86), the mycelium begins to branch after a 2-day incubation; over a 5-day incubation at ?2.8 MPa (a_w 0.98), it goes through a reproduction cycle, which culminates in spore formation. The mathematical model approach enabled us to elucidate the behavioral patterns of Streptomyces spores in a thin layer of agarized nutrient medium at low humidity levels. The dynamics of spore germination is governed by the exponential law, which allows calculation of the average duration of the period a before spore germination, as well as the time needed for 50% of viable spores to germinate.     

The composition of the chitinolytic microbial complex and its effect on chitin decomposition at various humidity levels

The dynamics of assimilation of chitin by soil microorganisms (primarily prokaryotes) as a source of carbon and nitrogen has been determined by gas chromatography and fluorescence microscopy. The highest rates of chitin decomposition in chernozem were detected at humidity levels corresponding to the pressure of soil moisture (P) of ?1.4 atm. The rate of microbial consumption of chitin is three times higher than that of the carbon of soil organic matter. Fluorescence microscopy revealed that an increase in the pressure of soil moisture from P = ?10 atm to P = ?0.7 atm resulted in a considerable increase in the proportion of the specific surface of mycelial bacteria (actinomycetes).     

The treatment of isolated genera

Problems presented by genera, or small groups of genera, which have been given family rank are reviewed, and the genera are divided into a number of categories according to the closeness of their affinity to other genera or families. Satellite genera that stand in close relation to families should be united with them. Binary families, that have been divided into two (or more) related families, should be re–united. Families connected by linking genera, should, logically, be united but practical considerations usually prevent this. Clusters of diverse but more or less distantly related genera present unusual problems, being treated either as several, often monogeneric families or as a loosely structured family. Truly isolated genera must be given family and often ordinal rank.