A note on single-channel autocorrelation functions

It is shown for time-reversible ion channel gating mechanisms that the sojourn time autocorrelation functions are necessarily nonnegative, decreasing, and convex. It is also shown, again for time-reversible mechanisms, that the lagged moments of all orders are determined by the first three moments. The application of these results to the statistical analysis of single-channel kinetics is briefly discussed.     

Comparative effects of trichothecene mycotoxins on bovine platelet function: Acetyl T-2 toxin,a more potent inhibitor than T-2 toxin

The effects of the trichothecene mycotoxins (acetyl T-2 toxin, T-2 toxin, HT-2 toxin, palmityl T-2 toxin, diacetoxyscirpenol (DAS), deoxynivalenol (DON), and T-2 tetraol) on bovine platelet function were examined in homologous plasma stimulated with platelet activating factor (PAF). The mycotoxins inhibited platelet function with the following order of potency: acetyl T-2 toxin > palmityl T-2 toxin = DAS > HT-2 toxin = T-2 toxin. While T-2 tetraol was completely ineffective as an inhibitor, DON exhibited minimal inhibitory activity at concentrations above 10×10^?4M. The stability of the platelet aggregates formed was significantly reduced in all mycotoxin treated platelets compared to that of the untreated PAF controls. It is suggested that the increased sensitivity of PAF stimulated bovine platelets to the more lipophilic mycotoxins may be related to their more efficient partitioning into the platelet membrane compared to the more hydrophilic compounds.     

Seed dispersal spectra: a comparison of temperate plant communities

Abstract. We compare the dispersal spectra of diaspores from varied plant communities in Australia, New Zealand, and North America, assigning dispersal mode to each diaspore type on the basis of apparent morphological adaptations. Species with ballistic and external dispersal modes were uncommon in most communities we surveyed. Ant dispersal was also rather uncommon, except in some Australian sclerophyll vegetation types. The frequency of vertebrate dispersal ranged up to 60% of the flora, the highest frequencies occurring in New Zealand forests. Wind dispersal ranged as high as 70% of the flora, with the highest values in Alaska, but usually comprised 10–30% of the flora. Many species in most communities had diaspores with no special morphological device for dispersal. Physiognomically similar vegetation types indifferentbiogeographic regions usually had somewhat dissimilar dispersal spectra. The frequency of dispersal by vertebrates often increased and the frequency of species with no special dispersal device decreased along gradients of increasing vertical diversity of vegetation structure. Elevation and moisture gradients also exhibited shifts in dispersal spectra. Within Australia, vertebrate- and wind-dispersal increased in frequency along a soil-fertility gradient, and dispersal by ants and by no special device decreased. Habitat breadths (across plant communities) and microhabitat breadths (within communities) for species of each major dispersal type did not show consistent differences, in general. Ant-dispersed species often had lower cover-values than other species in several Australian vegetation types. We discuss the ecological bases of these differences in dispersal spectra in terms of the availability of dispersal agents, seed size, and other ecological constraints. Seed size is suggested to be one ecological factor that is probably of general relevance to the evolution of dispersal syndromes.     

Inactivation of murine leukemia virus by compounds that react with the zinc finger in the viral nucleocapsid protein.

All retroviral nucleocapsid (NC) proteins, except those of spumaretroviruses, contain one or two copies of the conserved sequence motif C-X2-C-X4-H-X4-C. The conserved cysteine and histidine residues coordinate a zinc ion in each such motif. Rice et al. (W. G. Rice, J. G. Supko, L. Malspeis, R. W. Buckheit, Jr., D. Clanton, M. Bu, L. Graham, C. A. Schaeffer, J. A. Turpin, J. Domagala, R. Gogliotti, J. P. Bader, S. M. Halliday, L. Coren, R. C. Sowder II, L. 0. Arthur, and L. E. Henderson, Science 270:1194-1197, 1995) have described a series of compounds which inactivate human immunodeficiency virus type 1 (HIV-1) particles and oxidize the cysteine thiolates in the NC zinc finger. We have characterized the effects of three such compounds on Moloney murine leukemia virus (MuLV). We find that, as with HIV-1, the compounds inactivate cell-free MuLV particles and induce disulfide cross-linking of NC in these particles. The killed MuLV particles were found to be incapable of synthesizing full-length viral DNA upon infection of a new host cell. When MuLV particles are synthesized in the presence of one of these compounds, the normal maturational cleavage of the Gag polyprotein does not occur. The compounds have no effect on the infectivity of human foamy virus, a spumaretrovirus lacking zinc fingers in its NC protein. The resistance of foamy virus supports the hypothesis that the zinc fingers are the targets for inactivation of MuLV and HIV- I by the compounds. The absolute conservation of the zinc finger motif among oncoretroviruses and lentiviruses and the lethality of all known mutations altering the zinc-binding residues suggest that only the normal, wild-type structure can efficiently perform all of its functions. This possibility would make the zinc finger an ideal target for antiretroviral agents.     

Insights into the molecular basis of thermal stability from the structure determination of Pyrococcus furiosus gluatamate dehydrogenase

Abstract: The structure determination of the glutamate dehydrogenase from the hyperthermophile Pyrococcus furiosus has been completed at 2.2 Å resolution. The structure has been compared with the glutamate dehydrogenases from the mesophiles Clostridium symbiosum, Escherichia coli and Neurospora crassa . This comparison has revealed that the hyperthermophilic enzyme contains a striking series of networks of ion-pairs which are formed by regions of the protein which contain a high density of charged residues. Such regions are not found in the mesophilic enzymes and the number and extent of ion-pair formation is much more limited. The ion-pair networks are clustered at both inter domain and inter subunit interfaces and may well represent a major stabilising feature associated with the adaptation of enzymes to extreme temperatures.     

Confirmational identification of Escherichia coli, a comparison of genotypic and phenotypic assays for glutamate decarboxylase and beta-D-glucuronidase.

Genotypic and phenotypic assays for glutamate decarboxylase (GAD) and beta-D-glucuronidase (GUD) were compared for their abilities to detect various strains of Escherichia coli and to discriminate among other bacterial species. Test strains included nonpathogenic E. coli, three major groups of diarrheagenic E. coli, three other non-coli Escherichia species, and various other gram-negative and -positive bacteria found in water. The genotypic assays were performed with hybridization probes generated by PCR amplification of 670- and 623-bp segments of the gadA/B (GAD) and uidA (GUD) genes, respectively. The GAD enzymes catalyze the alpha-decarboxylation of L-glutamic acid to yield gamma-aminobutyric acid and carbon dioxide, which are detected in the phenotypic assay by a pH-sensitive indicator dye. The phenotypic assay for GUD involves the transformation of 4-methylumbelliferyl-beta-D-glucuronide to the fluorogenic compound 4-methylumbelliferone. The GAD phenotypic assay detected the majority of the E. coli strains tested, whereas a number of these strains, including all representatives of the O157:H7 serotype and several nonpathogenic E. coli strains, gave negative results in the GUD assay. Both phenotypic assays detected some but not all strains from each of the four Shigella species. A strain of Citrobacter freundii was also detected by the GUD assay but not by the GAD assay. All E. coli and Shigella strains were detected with both the gadA/B and uidA probes. A few Escherichia fergusonii strains gave weak hybridization signals in response to both probes at 65 degrees C but not at 68 degrees C. None of the other bacterial species tested were detected by either probe. These results were consistent with previous reports which have indicated that the GAD phenotypic assay detects a wider range of E. coli strains than does the GUD assay and is also somewhat more specific for this species. The genotypic assays for the two enzymes were found to be equivalent in both of these respects and superior to both of the phenotypic assays in terms of the range of E. coli strains and isolates detected.     

Biofilm ecology: On-line methods bring new insights into mic and microbial biofouling

Microbial biofilms were formed on coupons with defined coatings in once-through laminar flow fields of controlled bulk-phase composition and shear. Dilute media were utilized to select for biofilm growth. The formation, succession, and stability of the biofilms were monitored with non-destructive on-line methods (fluorescence, bioluminescence, attenuated total reflectance Fourier transform infrared spectrometry [ATR-FTIR] and electrochemical impedance spectroscopy) and by high resolution destructive analysts (viable and direct counts and phospholipid fatty acid signature methods) at the termination of the experiments. Biofilms of reproducible composition can be formed and the order of inoculation of multi-component biofilms affects their composition at harvest. The corrosion rates of mild steel depended on the biofilm composition but not the attached biomass. Examination of biofilms with the scanning vibrating electrode in a microscope field showed effects of heterogeneity in biofilm structure which promoted localized anodic activity. Pseudomonas stains were engineered to contain the lux gene cassette as a "reporter"; and the formation of the exopolymer alginate was shown not to promote attachment of the strain or secondary colonization by Vibrio. Examination of mutants forming different alginate structures showed differential attachment and biofilm structure. Studies of mutants of lipopolysaccharide structure showed differential attachment to substrata. Specific antifouling and fouling-release coatings showed a wide range of attachment and release properties as well as sublethal toxicity.     

Effects of external stimuli on environmental bacterial strains harboring analgD-lux bioluminescent reporter plasmid for the study of corrosive biofilms

An alginic acid biosynthesis bioluminescent reporter plasmid, pUTK50, was transconjugated into environmental strains ofPseudomonas putida, Pseudomonas fluorescens, andStenotrophomonas maltophilia. Bioluminescent transconjugates were selected from each strain for investigation of environmental stress factors that promote alginic acid exopolymer biosynthesis in developing biofilms. Environmental stimuli associated with increased levels of alginate synthesis, in a previously developed organism,P. aeruginosa FRD1, were applied to the environmental strains. Increased salt concentrations and higher ratios of nitrate vs ammonium ions as the limiting nitrogen source induced bioluminescence in FRD1 and the environmental strains. However, for environmental strains ofP. putida, P. fluorescens andS. maltophilia, polysaccharides were detected with low uronic acids content and different structural components. When tested within a biofilm,S. maltophilia O46 demonstrated exceptional adhesive and corrosive properties while alginic acid synthesis was not high. In most of the environmental strains, periods of increased bioluminescence were induced by external stimuli, but exopolysaccharides other than alginic acid were expressed. It is hypothesized that the environmental strains have homologous but nonidentical promoter sequences which are responsive to certain environmental stimuli and may control genes necessary for the production of alternative exopolysaccharides.