Inheritance of low-level resistance to penicillin, tetracycline, and chloramphenicol in Neisseria gonorrhoeae.

The genetics of low-level resistance to penicillin and other antibiotics in a clinical isolate and a multistep laboratory mutant of Neisseria gonorrhoea was studied by transformation. Mutations at three loci affected sensitivity to penicillin. Mutation at penA resulted in an eightfold increase in resistance to penicillin without affecting response to other antimicrobial agents. Mutation at ery resulted in a two- to fourfold increase in resistance to penicillin and similar increases in resistance to many other antibiotics, dyes, and detergents. Mutation at penB resulted in a fourfold increase in resistance to penicillin and tetracycline, the phenotypic expression of which was dependent on the presence of mutation at ery. The cumulative effect of mutations at penA, ery, and penB was an approximate 128-fold increase in penicillin resistance, to a minimum inhibitory concentration of 1.0 mug/ml. Low-level resistance to tetracycline or chloramphenicol was due to similar additive effects between mutations at the nonspecific ery and penB loci and a locus specific for resistance to each drug (tet and chl, respectively). No evidence was found for penicillinases or other drug-inactivating enzymes.     

High-frequency conjugal transfer of a gonococcal penicillinase plasmid.

Gonococci containing a 24 X 10(6)-dalton conjugal plasmid were able to mobilize for transfer a smaller, non-self-transmissible penicillinase (Pcr) plasmid with high frequency under appropriate conditions. In some strains, over 10% of donor colony-forming units transferred the Pcr plasmid in a mating of less than 2 h, which suggests that the conjugal system was naturally derepressed. Colony-opacity variants containing different quantities of an approximately 28,000-dalton outer membrane protein were altered in their ability to act as conjugal donors and recipients. Maximal transfer of the Pcr plasmid was observed between transparent donors and recipients, lacking appreciable amounts of the 28,000-dalton protein. Under conditions of high-frequency Pcr plasmid mobilization, no conjugal mobilization of chromosomal markers could be discerned.     

Amino Acid Transport in Suspension-cultured Plant Cells: II. CHARACTERIZATION OF l-LEUCINE UPTAKE

l-Leucine (l-Leu) transport into suspension cultured Nicotiana tabacum L. cv. Wisconsin 38 cells has been investigated. Cells were batch-cultured and routinely assayed 3.5 to 4 days after subculturing. Uptake rates were measured over the concentration range of 10 micromolar to 150 millimolar. Kinetic analysis of the uptake rates indicated that uptake was multiphasic with three saturable phases and one unsaturable phase. The three saturable phases which occur in the concentration ranges of 10 to 40 micromolar, 50 to 100 micromolar, and 0.2 to 5.0 millimolar exhibited the following characteristics; (a) phases were energy-dependent as shown by 84 to 94% inhibition of uptake rates by metabolic inhibitors; (b) phases exhibited broad pH optima between 3.0 and 5.5; (c) phases showed stereospecificity for l-Leu; (d) over a 12-hour incubation period, phases concentrated l-Leu 43, 90, and 10 times when the initial l-Leu concentration was 20 micromolar, 100 micromolar, and 1.0 millimolar, respectively; (e) phases had K(m) values of 17.6 micromolar, 60.1 micromolar, and 1.38 millimolar, respectively; and (f) in the temperature range of 17 to 27 C phases had Q(10) values of 2.1, 1.4, and 1.4, respectively. l-Leu uptake in the three saturable phases was inhibited by a 20-fold higher concentration of 18 other amino acids; phenylalanine, alanine, and methionine were the most effective inhibitors, whereas aspartic acid, asparagine, histidine, and arginine were the least effective. The nonsaturable phase which was responsible for increases in the uptake rate above 5.0 mm appeared to be primarily diffusional since it was minimally influenced by metabolic inhibitors and had a Q(10) of 1.3.     

Origin of the Vaccinia Virus Hemagglutinin

The relationship between the vaccinia virus hemagglutinin and hemadsorption was examined. Hemagglutinin synthesis was temporally related to the appearance of the hemadsorption reaction. Only chicken erythrocytes, which reacted with hemagglutinin, hemadsorbed to infected cells, and both of these reactions were inhibited by Ca(2+). The distribution of the vaccinia hemagglutinin and 5'-adenosine monophosphatase, a plasma membrane marker enzyme, in sucrose gradients was similar. Plasma membrane ghosts derived from infected cells hemadsorbed erythrocytes and yielded hemagglutinin upon sonic disruption. These data suggest that the majority of vaccinia hemagglutinin is derived from the plasma-membrane of the infected cell.     

Influence of electromagnetic fields on the efflux of calcium ions from brain tissue in vitro: a three-model analysis consistent with the frequency response up to 510 Hz

The frequency dependence of electromagnetic field-induced calcium-ion efflux from chicken brain tissues has been examined at 15-Hz intervals over the range 1-510 Hz. The electric field component was 15 Vrms/m and the magnetic component varied between 59 and 69 nTrms. No patterns of response as a function of frequency could be readily discerned when the differences in mean efflux values between exposed and sham samples were compared. However, the calculated P-value, a function that combines at each frequency the difference between the means of the exposed and sham groups with the variance of each group, does provide a basis for hypothesizing the existence of three frequency-dependent patterns in the data. One pattern includes all the highly significant (P less than .01) responses which occur between 15 and 315 Hz, at 30-Hz intervals; two independent trials at 165 Hz, giving nonsignificant responses (P greater than .5), break this pattern into two groups of five frequencies each, which is contrary to the expected result for a simple Lorentz-force interaction. However, another pattern of significant results at 60, 90, and 180 Hz, but not at 300 Hz, is consistent with a Lorentz-force model. A third pattern, composed of only one significant response at 405 Hz, is very close to the resonance predicted on a linear extrapolation from high-frequency data for 13carbon atoms. This hypothetical ordering of the frequency-response profile provides the basis for future experimental designs to test each possible interaction model and for their connection to the calcium-ion efflux endpoint.     

High levels of recombination induced by homologous P elements in Drosophila melanogaster

Summary P element transposons in Drosophila melanogaster are capable of mobilizing incomplete P elements elsewhere in the genome, and of inducing recombination. This recombination is usually only of the order of 1% or less. We show that two P elements, located at exactly homologous sites, induce levels of recombination of 20% or higher. The recombination appears to be exact, as determined by the lack of phenotypic effects in recombinant products and the lack of size changes detectable by Southern hybridization. Female recombination is increased, but to a lesser extent than male recombination. Somatic recombination levels are also elevated. Alternative explanations for the high recombination levels are given in terms of the consequences of repair of an excision site and in terms of recombination as part of the replicative transposition process.     

Localisation of the amathamide alkaloids in surface bacteria of Amathia wilsoni Kirkpatrick, 1888 (Bryozoa: Ctenostomata)

The marine bryozoan Amathia wilsoni contains several brominated secondary metabolites, the alkaloid amathamides A–F. Energy dispersive X-ray analysis coupled with scanning electron microscopy was used to localise bromine in sections of Amathia wilsoni. Bromine concentrations higher than background levels were only found on the surface of the bryozoan and not within any of the different internal cell types. The correlation between bromine levels and a rod-shaped bacterium, ubiquitous to the tip region, points to the bacterium being closely associated with the range of amathamides found in Amathia wilsoni.