Prokaryotic microbial ecology as an ecosurveillance tool for eukaryotic pathogen colonisation: Meiothermus and Naegleria fowleri

Naegleria fowleri has been detected in drinking water distribution systems (DWDS) in Australia, Pakistan and the United States and is the causative agent of the highly fatal disease primary amoebic meningoencephalitis. Previous small scale field studies have shown that Meiothermus may be a potential biomarker for N. fowleri. However, correlations between predictive biomarkers in small sample sizes often breakdown when applied to larger more representative datasets. This study represents one of the largest and most rigorous temporal investigations of Naegleria fowleri colonisation in an operational DWDS in the world and measured the association of Meiothermus and N. fowleri over a significantly larger space and time in the DWDS. A total of 232 samples were collected from five sites over three-years (2016-2018), which contained 29 positive N. fowleri samples. Two specific operational taxonomic units assigned to M. chliarophilus and M. hypogaeus, were significantly associated with N. fowleri presence. Furthermore, inoculation experiments demonstrated that Meiothermus was required to support N. fowleri growth in field-collected biofilms. This validates Meiothermus as prospective biological tool to aid in the identification and surveillance of N. fowleri colonisable sites.

Surface plasmon excitation on a grating assisted by a cholesteric liquid crystal layer

While surface plasmon excitation assisted by nematic liquid crystal layers has been comprehensively studied in different aspects, application of cholesteric structures for surface plasmon excitation remains an unexplored area. Moreover, structures including cholesteric layers and metal grating for surface plasmon excitation have never been considered, to the best of our knowledge. We studied theoretically and experimentally such structures focusing on different regimes of propagation of normal modes in the cholesteric liquid crystal layer. The application of such structures for sensing is accordingly discussed.

Electrospray ion beam deposition: soft-landing and fragmentation of functional molecules at solid surfaces

The ion beam deposition (IBD) of rhodamine dye molecules on solid surfaces in high vacuum is explored in order to characterize the possibility of fabricating molecular coatings or nanostructures from nonvolatile molecules. Molecular ion beams with a well-defined composition are deposited on silicon oxide surfaces with a controlled kinetic energy. Photoluminescence spectroscopy and time-of-flight secondary ion mass spectrometry (TOF-SIMS) are employed in order to characterize the sample with respect to coverage, homogeneity, and the fraction of intact landed ions (soft-landing ratio). We find that homogeneous rhodamine films of defined composition can be produced at energies of 2-100 eV. The coverage is found to be proportional to the ion dose. Soft-landing is observed for energies up to 35 eV.

Magic alkali-fullerene compound clusters of extreme thermal stability

The thermal stability of free pure C60-, as well as C60-alkali, and -alkaline-earth metal compound clusters is investigated. We find that small (C60)m-clusters (m<or=6) decay at comparatively low temperatures below 400 K, as a consequence of weak intermolecular van der Waals interaction. Adding barium or potassium to the clusters dramatically increases the decay temperatures for "magic" configurations of (C60)mBa(2m-1) and (C60)mK(2m), which reach values as high as 1780 K. Contrary to common belief, the superstable compound clusters are not characterized by filled geometrical or electronic shells. Density functional calculations show that the delicate interplay of ionic (K, Ba) and covalent (Ba) interaction between C60 and the metal atoms, on the one hand, and entropic contributions to the Gibbs free energy, on the other hand, determine the unusual stability.

Fluorometric determination of 2'-beta-fluoro-2',3'-dideoxyadenosine 5'-triphosphate, the active metabolite of a new anti-human immunodeficiency virus drug, in human lymphocytes

A sensitive precolumn derivatization method has been developed to measure the 5'-triphosphate of 2'-beta-fluoro-2',3'-dideoxyadenosine (F-ddA, lodenosine), a new anti-HIV drug, in human lymphocytes by HPLC using fluorescence detection. Reaction of chloroacetaldehyde with F-ddA triphosphate in extracts from human lymphocytes produces a highly fluorescent etheno adduct. This derivative is then separated and quantitated by reverse-phase paired-ion chromatography. Degradation of natural nucleic acid ribosides, such as ATP, using periodate oxidation simplifies the chromatogram and minimizes interference with detection of the target analyte. This method, modeled using cultured MOLT-4 T-lymphocytes, achieves a linear detector response for peak area measurements over the range 2.5 to 22.5 pmol (50-450 nM using 50 microl sample). Analyte recovery is greater than 90%, and the method achieves a limit of detection and limit of quantitation of 1.4 and 2.5 pmol per HPLC injection (50 microl sample containing cellular extract from 2.5 x 10(6) cells), respectively. Application of this method to measure F-ddATP in peripheral blood mononuclear cells from HIV-infected patients treated with F-ddA at 3.2 mg/kg twice daily for 22 days shows F-ddATP levels which range from 1.5 to 3.5 pmol/10(6) cells.

Cyclopentenyl uracil: an effective inhibitor of uridine salvage in vivo

Cyclopentenyl uracil, a non-cytotoxic inhibitor of uridine kinase, was found to effectively block the salvage of circulating uridine by host and tumor tissues in the intact mouse. Dose-response characteristics of the inhibition were determined. Large doses (1 g/kg) of cyclopentenyl uracil were required, and the effect of a single dose fell rapidly over a 24-hr period. A sustained inhibition of uridine salvage of > 64-79% could be maintained by multiple doses of 1 g/kg given on an every 8-hr schedule. Mice given cyclopentenyl uracil (1 g/kg) every 8 hr for 5 days continued to gain weight and showed no signs of toxicity; however, the combination of cyclopentenyl uracil with a non-toxic dose of N-(phosphonacetyl)-L-aspartic acid (PALA; 200 mg/kg daily for 5 days) was lethal to mice, indicating that circulating uridine modifies the toxicity of agents that act on enzymes of the de novo pyrimidine pathway. Although the duration of action and potency of cyclopentenyl uracil are not ideal, this is the first demonstration of an effective inhibition of uridine salvage in the intact mouse with a non-cytotoxic agent. This makes possible the evaluation of concurrent inhibition of de novo and salvage routes to pyrimidine nucleotides as an approach to chemotherapy.

Uptake and metabolism of myo-inositol by L1210 leukaemia cells

The initial rate of uptake of [3H]myo-inositol by L1210 murine leukaemia cells is directly proportional to the extracellular concentration and unaffected by several analogues of myo-inositol even at millimolar concentrations. Scyllitol, a geometric isomer of myo-inositol, partially inhibited the uptake of myo-inositol (40% at 0.1 mM). A portion of the uptake of myo-inositol was not inhibited even at 5 mM-scyllitol. At steady-state the intracellular concentration of [3H]myo-inositol is directly proportional to the extracellular concentration. Addition of myo-inositol to medium does not enhance the growth of L1210 cells; these cells can maintain an extracellular concentration of 20 microM-myo-inositol even when grown in myo-inositol-free medium. Synthesis of myo-inositol from glucose by L1210 cells was demonstrated by use of [13C]glucose and m.s. L1210 cells maintain myo-inositol pools by a combination of synthesis de novo and uptake of exogenous myo-inositol by either passive diffusion or a low affinity carrier.

Substrate properties of analogs of myo-inositol

The hydrolysis of the minor cell membrane lipid phosphatidylinositol-4,5-bisphosphate mediates the action of many growth factors and hormones. As an approach to the development of specific inhibitors of this process, we have synthesized a series of analogs of myo-inositol and have evaluated their ability to serve as substrates for phosphatidylinositol synthetase. Modification at the 2-, 3-, or 4-positions produced compounds unable to serve as substrates, but several 5-modified analogs retained activity as substrates of phosphatidylinositol synthetase. The product formed from 5-deoxy-5-fluoro-myo-[3H]inositol by phatidylinositol synthetase was hydrolyzed by phospholipase D and gave 5-deoxy-5-fluoro-myo-inositol as the radiolabeled product. Two analogs, 5-deoxy-myo-inositol and 5-deoxy-5-fluoro-myo-inositol, were shown to permeate L1210 leukemia cells and be incorporated into cellular phospholipid. Analysis of the radiolabeled lipids formed on incubation of L1210 cells with 5-deoxy-5-fluoro-myo-[3H]inositol indicated that the fradulent lipid formed was further phosphorylated to the monophosphate but not to the diphosphate form.

D-myo-inositol (1,4)-bisphosphate 1-phosphate. Partial purification from rat liver and characterization

A specific 1-phosphatase acting on myo-inositol (1,4)-biphosphate with a high affinity (Km = 0.9 microM) has been purified 49-fold from soluble proteins of rat liver by anion exchange chromatography followed by gel filtration. This enzyme has a molecular weight of 58,000 as estimated by gel filtration, a pH optimum of 7.5, and requires Mg++ for activity. The only product formed from myo-inositol (1,4)-bisphosphate is the 4-monophosphate. Of 7 other inositol phosphates examined only myo-inositol (1,3,4)-triphosphate was a substrate.

The effect of 3-deazauridine and dipyridamole on uridine utilization by mice

The inhibition of uridine utilization by 3-deazauridine, an inhibitor of uridine kinase, and by dipyridamole, an inhibitor of the facilitated transport of nucleosides was examined. 3-Deazauridine (500 mg/kg) markedly inhibited (greater than 70%) the formation of uracil nucleotides from uridine in liver, kidney, and L1210 tumor cells. The degree of inhibition is greatly reduced by 6 hr after administration of the drug. Dipyridamole (100 mg/kg) did not significantly reduce salvage of uridine by liver or kidney and produced only small, transient reductions in salvage by L1210 tumors. Dipyridamole pretreatment did not alter the rate of clearance of uridine from the plasma.

Inhibition of uridine kinase and the salvage of uridine by modified pyrimidine nucleosides

Uridine kinase can play a crucial role in the provision of pyrimidine nucleotides for cellular nucleic acid synthesis, particularly when de novo synthesis is inhibited by chemotherapeutic agents. Therefore, uridine kinase is an attractive target for drug development. We examined a series of 29 analogs of uridine, most with modifications at the 5'-position, as inhibitors of uridine kinase in vitro and of uridine salvage by intact L1210 cells. Substitution at the 5'-position resulted in decreased efficacy as inhibitors of uridine kinase, particularly if the substituent was large. None of the analogs with 5'-position modifications effectively inhibited salvage of uridine by intact L1210 cells. Four carbocyclic pyrimidine nucleoside analogs (one series) were all effective competitive inhibitors of uridine kinase and of uridine salvage by intact L1210 cells. Cyclopentenyl uracil 19 shows promise for further development as it inhibits uridine salvage at nontoxic concentrations.

Salvage of circulating pyrimidine nucleosides by tissues of the mouse

The metabolism of pyrimidine nucleosides present in the plasma of the mouse has been examined. Uridine and cytidine are rapidly cleared from the circulation with t1/2 of less than 5 min. Uracil, deoxycytidine, deoxyuridine, and thymidine are cleared more slowly with t1/2 of 9 to 13 min. Various tissues differed markedly in the extent of nucleotide formation from circulating nucleosides. Cytidine and uridine are predominantly converted to nucleotides (greater than 50%) rather than catabolized, whereas uracil is almost entirely degraded. Thymidine, deoxyuridine, and deoxycytidine are intermediate in the extent of their conversion to nucleotides: 8.9 to 21% of these nucleosides are salvaged in the mouse. Both anabolic and catabolic routes are important in the metabolism of pyrimidine nucleosides in vivo.