The role of bacterial growth autoregulators (alkyl hydroxybenzenes) in the response of staphylococci to stresses

The investigation of the response of a batch culture of Staphylococcus aureus to exogenous alkyl-substituted hydroxybenzenes (AHBs), chemical analogues of anabiosis autoinducers, showed that C1-AHB at concentrations from 5 microM to 1.5 mM did not influence the culture growth, whereas the more hydrophobic C6-AHB inhibited it at concentrations of 0.5 mM and higher. Either of the AHBs drastically enhanced the phenotypic dissociation of staphylococcal cultures, which manifested itself in an increase in the fraction of cells producing small nonhemolyzing colonies of G type when plated on solid media with erythrocytes. In a submerged staphylococcal culture, the relative number of cells producing G-type colonies varied from 10 to 90%, depending on the concentration of the AHB added. The growth of S. aureus in the presence of AHBs also enhanced cell tolerance to heat shock (heating at 45 or 60 degrees C for 10 min). The role of AHBs, which are structural modifiers of membranes and possess chaperone activity, in the mechanisms responsible for cell tolerance and phenotypic dissociation of microbial populations is discussed.     

The role of microbial dormancy autoinducers in metabolism blockade

Alkyl-substituted hydroxybenzenes (AHBs), which are autoinducers of microbial dormancy (d ₁ factors), were found to stabilize the structure of protein macromolecules and modify the catalytic activity of enzymes. In vitro experiments showed that C₆-AHB at concentrations from 10⁻⁴ to 10⁻² M, at which it occurs in the medium as a true solution and a micellar colloid, respectively, nonspecifically inhibited the activity of chymotrypsin, RNase, invertase, and glucose oxidase. C⁶-AHB-induced conformational alterations in protein macromolecules were due to the formation of complexes, as evidenced by differences in the fluorescence spectra of individual RNase and C₆-AHB and their mixtures and in the surface tension isotherms of C₆-AHB and trypsin solutions. Data on the involvement of dormancy autoinducers in the posttranslational modification of enzymes and their inhibition will provide further insight into the mechanisms of development and maintenance of dormant microbial forms.     

Partitioning of 2,6-Bis(1H-Benzimidazol-2-yl)pyridine fluorophore into a phospholipid bilayer: complementary use of fluorescence quenching studies and molecular dynamics simulations

Successful use of fluorescence sensing in elucidating the biophysical properties of lipid membranes requires knowledge of the distribution and location of an emitting molecule in the bilayer. We report here that 2,6-bis(1H-benzimidazol-2-yl)pyridine (BBP), which is almost non-fluorescent in aqueous solutions, reveals a strong emission enhancement in a hydrophobic environment of a phospholipid bilayer, making it interesting for fluorescence probing of water content in a lipid membrane. Comparing the fluorescence behavior of BBP in a wide variety of solvents with those in phospholipid vesicles, we suggest that the hydrogen bonding interactions between a BBP fluorophore and water molecules play a crucial role in the observed “light switch effect”. Therefore, the loss of water-induced fluorescence quenching inside a membrane are thought to be due to deep penetration of BBP into the hydrophobic, water-free region of a bilayer. Characterized by strong quenching by transition metal ions in solution, BBP also demonstrated significant shielding from the action of the quencher in the presence of phospholipid vesicles. We used the increase in fluorescence intensity, measured upon titration of probe molecules with lipid vesicles, to estimate the partition constant and the Gibbs free energy (ΔG) of transfer of BBP from aqueous buffer into a membrane. Partitioning BBP revealed strongly favorable ΔG, which depends only slightly on the lipid composition of a bilayer, varying in a range from − 6.5 to − 7.0 kcal/mol. To elucidate the binding interactions of the probe with a membrane on the molecular level, a distribution and favorable location of BBP in a POPC bilayer were modeled via atomistic molecular dynamics (MD) simulations using two different approaches: (i) free, diffusion-driven partitioning of the probe molecules into a bilayer and (ii) constrained umbrella sampling of a penetration profile of the dye molecule across a bilayer. Both of these MD approaches agreed with regard to the preferred location of a BBP fluorophore within the interfacial region of a bilayer, located between the hydrocarbon acyl tails and the initial portion of the lipid headgroups. MD simulations also revealed restricted permeability of water molecules into this region of a POPC bilayer, determining the strong fluorescence enhancement observed experimentally for the membrane-partitioned form of BBP.     

Isolation and characterization of nitrogen-fixing bacteria of the genus <Emphasis Type="Italic">Azospirillum</Emphasis> from the soil of a <Emphasis Type="Italic">Sphagnum</Emphasis> peat bog

he presence of nitrogen-fixing bacteria of the genus Azospirillum in the soils of acidic raised Sphagnum bogs is revealed for the first time. Three Azospirillum strains, B2, B21, and B22, were isolated as a component of methane-oxidizing enrichment cultures, whereas attempts to isolate them directly from peat samples have failed. The results of comparative analysis of the nucleotide sequences of 16S rRNA genes, DNA-DNA hybridization, and the analysis of the sequences of the functional genes encoding nitrogenase and ribulose-1, 5-bisphosphate carboxylase reveal that all the newly obtained strains can be classified as Azospirillum lipoferum. Yet, unlike A. lipoferum, the isolates do not require biotin and utilize sucrose, inositol, and glycerol for growth. The cell morphology of strain B2 differs from that of the type strain and strains B21 and B22. The results obtained indicate the variability of morphological, physiological, and biochemical properties in closely related Azospirillum strains and suggest the existence of metabolic relationships between methanotrophic bacteria and the representatives of the genus Azospirillum under peat bog conditions.     

Glands in the olfactory epithelium of marine fish

Specific features of the morphohistochemical and ultrastructural organization of the secretory system of olfactory organs in marine fish from the Pacific region were studied. Multicellular alveolar and tubular glands were revealed in the olfactory epithelium of Pleurogrammus azonus, Myoxocephalus yaok, Enophrys diceraus, Alcichthys elongatus, Gymnocanthus pistilliger, Hemilepidotus gilberti, Hemitripterus villosus, Podothecus veternus, Liparis dubius, Clupea pallasi, as well as in salmonids (Oncorhynchus nerka, O. keta, O. gorbuscha, O. masou, O. kisutch, O. tschawytscha) and in tetraodontids (Takifugu rubripes). The morphofunctional characteristic of the described glands is close to the Bowman’s glands of land animals. The structure, localization, and density of location of olfactory glands are determined by specific features of the ecology of the species. These structures are most numerous in bottom and near-bottom representatives of marine ichthyofauna.     

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%.     

Sucrose utilization determinants of transposon Tn2555

The Sac- -derivatives of the plasmid pBRS5.2 containing the sucrose utilization transposon Tn2555 were obtained by using the insertional mutagenesis. The sac mutations were mapped within the transposons DNA fragment of about 3kb. The existence of two linkage groups of the sac mutations was shown by complementation analysis. Among the gene products of Tn2555 the polypeptides of about 58, 36, 27, 14 and 12 kd were found. The data on relation of the sac genes of Tn2555 and the ones of the known plasmid pUR400 of Salmonella typhimurium are discussed.     

A three-barrier model for describing the energy profile of the calcium channel in the molluscan neuron membrane

From measurements of shifts of current-voltage characteristics for the calcium current of the neuron membrane ofHelix pomatia the density (c) and binding constants of the bivalent cations (k_M) were calculated for charged groups on its outer surface =0.23 e^–/nm², K_Ca=70 liters/mole, K_Sr=40 liters/mole, and K_Ba=20 liters/mole. These values were used to determine the concentration of carrier ions in the extracellular solution near the membrane and the true position of the current-voltage characteristic curves of calcium channels relative to the voltage axis. The three-carrier model was used to calculate the energy profile of the calcium channel. Values of dissociation constants with an external binding site were 10 and 91 mM for calcium and barium ions, respectively. The pK titration value of this site was 5.8. It is concluded that the strength of the inward ionic current through the channel is determined primarily by the energy of interaction between the carrier ion and the external binding site, which evidently contains one carboxyl group. This current is inhibited when the intracellular calcium ion concentration reaches a level at which the degree of occupancy of the internal binding site is significantly less than unity, a state of affairs which may arise as a result of the indirect effect of these ions through the cyclic nucleotide metabolic system.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 13, No. 3, pp. 322–331, May–June, 1981.