Coherent light scattering from a telecom C-band quantum dot

Quantum networks have the potential to transform secure communication via quantum key distribution and enable novel concepts in distributed quantum computing and sensing. Coherent quantum light generation at telecom wavelengths is fundamental for fibre-based network implementations, but Fourier-limited emission and subnatural linewidth photons have so far only been reported from systems operating in the visible to near-infrared wavelength range. Here, we use InAs/InP quantum dots to demonstrate photons with coherence times much longer than the Fourier limit at telecom wavelength via elastic scattering of excitation laser photons. Further, we show that even the inelastically scattered photons have coherence times within the error bars of the Fourier limit. Finally, we make direct use of the minimal attenuation in fibre for these photons by measuring two-photon interference after 25 km of fibre, demonstrating finite interference visibility for photons emitted about 100,000 excitation cycles apart.

A quantum light-emitting diode for the standard telecom window around 1,550 nm

Single photons and entangled photon pairs are a key resource of many quantum secure communication and quantum computation protocols, and non-Poissonian sources emitting in the low-loss wavelength region around 1,550 nm are essential for the development of fibre-based quantum network infrastructure. However, reaching this wavelength window has been challenging for semiconductor-based quantum light sources. Here we show that quantum dot devices based on indium phosphide are capable of electrically injected single photon emission in this wavelength region. Using the biexciton cascade mechanism, they also produce entangled photons with a fidelity of 87 ± 4%, sufficient for the application of one-way error correction protocols. The material system further allows for entangled photon generation up to an operating temperature of 93 K. Our quantum photon source can be directly integrated with existing long distance quantum communication and cryptography systems, and provides a promising material platform for developing future quantum network hardware.

Quantum teleportation of laser-generated photons with an entangled-light-emitting diode

Quantum teleportation can transfer information between physical systems, which is essential for engineering quantum networks. Of the many technologies being investigated to host quantum bits, photons have obvious advantages as 'pure' quantum information carriers, but their bandwidth and energy is determined by the quantum system that generates them. Here we show that photons from fundamentally different sources can be used in the optical quantum teleportation protocol. The sources we describe have bandwidth differing by a factor over 100, but we still observe teleportation with average fidelity of 0.77, beating the quantum limit by 10 standard deviations. Furthermore, the dissimilar nature of our sources exposes physics hidden in previous experiments, which we also predict numerically. These phenomena include converting qubits from Poissonian to Fock statistics, quantum interference, beats and teleportation for spectrally non-degenerate photons, and acquisition of evolving character following teleportation of a qubit.

Indistinguishable entangled photons generated by a light-emitting diode

A linear optical quantum computer relies on interference between photonic qubits for logic, and entanglement for near-deterministic operation. Here we measure the interference and entanglement properties of photons emitted by a quantum dot embedded within a light-emitting diode. We show that pairs of simultaneously generated photons are entangled, and indistinguishable from subsequently generated photons. We measure entanglement fidelity of 0.87 and two-photon-interference visibility of 0.60 ± 0.05. The visibility, limited by detector jitter, could be improved by optical cavity designs.

Exciton-spin memory with a semiconductor quantum dot molecule

We report on a single photon and spin storage device based on a semiconductor quantum dot molecule. Optically excited single electron-hole pairs are trapped within the molecule, and their recombination rate is electrically controlled over 3 orders of magnitude. Single photons are stored up to 1 μs and read out on a subnanosecond time scale. By using resonant excitation, the circular polarization of individual photons is transferred into the spin state of electron-hole pairs with a fidelity above 80%, which does not degrade for storage times up to the 12.5 ns repetition period of the experiment.

Spatially resolved measurements of laser filamentation in long scale length underdense plasmas with and without beam smoothing

The onset of filamentation, following the interaction of a relatively long (τ(L)≃1  ns) and intense (I(L)≃5×10(14)  W/cm(2)) laser pulse with a neopentane filled gas bag target, has been experimentally studied via the proton radiography technique, in conditions of direct relevance to the indirect drive inertial confinement fusion scheme. The density gradients associated with filamentation onset have been spatially resolved yielding direct and unambiguous evidence of filament formation and quantitative information about the filamentation mechanism in agreement with previous theoretical modelings. Experimental data confirm that, once spatially smoothed laser beams are used, filamentation is not a relevant phenomenon during the heating laser beams propagation through typical hohlraum gas fills.

Bell-inequality violation with a triggered photon-pair source

Here we demonstrate, for the first time, violation of Bell's inequality using a triggered quantum dot photon-pair source without post-selection. Furthermore, the fidelity to the expected Bell state is increased above 90% using temporal gating to reject photons emitted at times when collection of uncorrelated light is more probable. A direct measurement of a CHSH Bell inequality is made showing a clear violation, highlighting that a quantum dot entangled photon source is suitable for communication exploiting nonlocal quantum correlations.

Coherence of an entangled exciton-photon state

We study the effect of the exciton fine-structure splitting on the polarization entanglement of photon pairs produced by the biexciton cascade in a quantum dot. Entanglement persists despite separations between the intermediate energy levels of up to 4 microeV. Measurements show that entanglement of the photon pair is robust to the dephasing of the intermediate exciton state responsible for the first-order coherence time of either single photon. We present a theoretical framework incorporating the effects of spin scattering, background light, and dephasing. We distinguish between the first-order coherence time, and a parameter which we measure for the first time and define as the cross-coherence time.

Biphoton interference with a quantum dot entangled light source

We demonstrate optical interferometry beyond the limits imposed by the photon wavelength using 'triggered' entangled photon pairs from a semiconductor quantum dot. Interference fringes of the entangled biphoton state reveals a periodicity half of that obtained with the single photon, and much less than that of the pump laser. High fringe visibility indicates that biphoton interference is less sensitive to decoherence than interference of two sequential single photons. The results suggest that quantum interferometry may be possible using a semiconductor LED-like device.

A semiconductor source of triggered entangled photon pairs

Entangled photon pairs are an important resource in quantum optics, and are essential for quantum information applications such as quantum key distribution and controlled quantum logic operations. The radiative decay of biexcitons-that is, states consisting of two bound electron-hole pairs-in a quantum dot has been proposed as a source of triggered polarization-entangled photon pairs. To date, however, experiments have indicated that a splitting of the intermediate exciton energy yields only classically correlated emission. Here we demonstrate triggered photon pair emission from single quantum dots suggestive of polarization entanglement. We achieve this by tuning the splitting to zero, through either application of an in-plane magnetic field or careful control of growth conditions. Entangled photon pairs generated 'on demand' have significant fundamental advantages over other schemes, which can suffer from multiple pair emission, or require post-selection techniques or the use of photon-number discriminating detectors. Furthermore, control over the pair generation time is essential for scaling many quantum information schemes beyond a few gates. Our results suggest that a triggered entangled photon pair source could be implemented by a simple semiconductor light-emitting diode.

Evidence for high-efficiency laser-heated hohlraum performance at 527 nm

A series of experiments conducted on the HELEN laser system [M. J. Norman, Appl. Opt.4120023497], into thermal x-ray generation from hohlraum targets using 527 nm (2omega) wavelength laser light, has shown that it is possible to exceed radiation temperatures previously thought limited by high levels of superthermal or hot electron production or stimulated backscatter. This Letter questions whether the assumptions traditionally applied to hohlraum design with respect to hot plasma filling and the use of 2omega light are too conservative.

Host factors associated with the detection of Aeromonas salmonicida and Yersinia ruckeri in Ontario, Canada government fish hatcheries

This paper presents an epidemiological investigation of Ontario Ministry of Natural Resources Fish Health Laboratory data from 1981 to 1997, to determine whether fish species and age were associated with lot-level detection of Aeromonas salmonicida and Yersinia ruckeri in hatchery fish. In stepwise logistic regression, the species brook trout and back-cross (lake trout crossed with the hybrid "splake") were more likely to test A. salmonicida-positive compared to all other species reared in the hatcheries. Similarly, the species brook trout was significantly more likely to test Y. ruckeri-positive compared to all other species. For both pathogens, the 1-5-month age group was associated significantly with detection. These findings suggest that purposive sampling of higher-risk fish lots could increase the likelihood of detecting both study pathogens.

Continuous wave observation of massive polariton redistribution by stimulated scattering in semiconductor microcavities

A massive redistribution of the polariton occupancy to two specific wave vectors, zero and approximately 3.9x10(4) cm(-1), is observed under conditions of continuous wave excitation of a semiconductor microcavity. The "condensation" of the polaritons to the two specific states arises from stimulated scattering at final state occupancies of order unity. The stimulation phenomena, arising due to the bosonic character of the polariton quasiparticles, occur for conditions of resonant excitation of the lower polariton branch. High energy nonresonant excitation, as in most previous work, instead leads to conventional lasing in the vertical cavity structure.

Angle-resonant stimulated polariton amplifier

We experimentally demonstrate resonant coupling between photons and excitons in microcavities which can efficiently generate enormous single-pass optical gains approaching 100. This new parametric phenomenon appears as a sharp angular resonance of the incoming pump beam, at which the moving excitonic polaritons undergo very large changes in momentum. Ultrafast stimulated scattering is clearly identified from the exponential dependence on pump intensity. This device utilizes boson amplification induced by stimulated energy relaxation.

Effects of hen egg yolk immunoglobulin in passive protection of rainbow trout against Yersinia ruckeri

Anti-Yersinia ruckeri egg yolk immunoglobulin (IgY) was transferred to egg yolk after immunization of White Leghorn hens with formalin-killed whole cells of serovar 1 (RS1154) and serovar 2 (RS1153)Y. ruckeri and its lipopolysaccharide (LPS). The IgY was specific for its homologous LPS in western immunoblot, whereas some protein bands were commonly recognized, even by IgY from eggs of unimmunized hens. Purified LPS from both Y. ruckeri serovar types 1 and 2 had a very poor immunogenicity. The IgY activity was stable when processed into pellet form by a microbial transglutaminase treatment and showed a considerable resistance against acid pepsin for at least 2 h. Feeding specific anti-serovar 1 Y. ruckeri IgY to fish either before or after immersion infection produced marginal reductions in mortalities and in intestine infection. The same IgY did passively protect rainbow trout against infection when administered by intraperitoneal injection 4 h before an immersion challenge.

Production of the 57 kDa major surface antigen by a non-agglutinating strain of the fish pathogen Renibacterium salmoninarum

The major surface antigen of Renibacterium salmoninarum, p57, is associated with cell autoagglutination and implicated as a virulence factor in fish infections. An autoagglutinating strain, JD24, caused 92% mortality when 2 x 10(7) cells were injected intraperitoneally into rainbow trout Oncorhynchus mykiss, while a non-agglutinating strain, MT 239, produced only 7% mortality after 100 d. The p57 antigen was present in the supernates of broth cultures of both strains when examined by western immunoblotting, and the gene for p57 was detected in both strains by PCR. Electron microscopy of cryopreserved thin sections showed an amorphous layer associated with the cell surface of JD24 which was not seen with MT 239. While p57 from JD24 could reassociate with cells of both strains, p57 from MT 239 failed to restore haemagglutination activity to either strain. Biotinylation of bacterial surfaces demonstrated the presence of a carbohydrate component of p57 from JD24 which was absent from the p57 produced by MT 239. The higher virulence of JD24 may depend not only on the production of p57, but also its direct association with the bacterial cell surface.

The natural decomposition of adipocere

Adipocere is a waxy substance which sometimes forms from the adipose tissue of dead bodies, especially when they are under water. A disinterment in southern Ontario lead to the recovery of extensive adipocere from an interment which occurred in AD 1869. Subsequent laboratory research was designed to explore the conditions under which adipocere will disappear, the goal being to identify strategies for estimating a range of time since death in cases where adipocere is present. Varieties of aerobic or facultatively anaerobic microorganisms from the surface of the adipocere were separated and identified. In culture, the gram positive bacteria were able to degrade the adipocere. We propose that the persistence of adipocere is related to the exclusion of gram positive bacteria from the burial environment. The role of bacteria in adipocere formation and degradation must be understood before we can use the presence of adipocere to extrapolate information about the post-death interval.

Immunization with bacterial antigens: yersiniosis

Yersinia ruckeri causes salmonid fish diseases called yersiniosis or enteric redmouth disease (ERM). Isolates include several serological varieties and disease outbreaks are frequently associated with stress or poor environmental factors. As a result, it is difficult to define clearly the significant virulence factors and pathogenic mechanisms of the bacterium, which introduces uncertainties about the appropriate formulation of bacterins for immunization. An enteric redmouth bacterin was the first commercially-produced fish vaccine, and the formalin-killed whole-cell product continues to be highly effective whether administered by immersion, spray, injection, or oral routes. Serovar 1, "Hagerman" strains are the basis for most commercial bacterins, and serovar 2 is not included, despite epizootics in chinook salmon and brook trout. Vaccination studies report different degrees of cross-protection between serogroups of Y. ruckeri, but the basis for the cross-protection is not clear. Lipopolysaccharide (LPS) of serovar 1 Y. ruckeri elicits negligible or weak antibody responses in fish and low cell-proliferation memory responses compared with serovar 2 strains. These observations raise fundamental questions about the kinds of immune responses that are involved in the highly effective vaccine-protection provided by commercial vaccines.

Binary phase zone-plate arrays for laser-beam spatial-intensity distribution conversion

We report on the theory and development of a diffractive element composed of a binary phase zone-plate array. This component conditions the intensity distribution in the focal plane of a conventional refractive lens to generate efficiently (82%) a flattop intensity envelope on target. Analysis of the design indicates that manufacturing tolerances are not critical. Experimental performances on target from x-ray emission and shock-breakout measurements are also presented.

Binary-phase zone plate arrays for the generation of uniform focal profiles

The generation of uniform focal intensity profiles is important for a number of applications, including laser-plasma interaction experiments. We report on a focusing system that uses a novel binary-phase optic capable of producing efficient two-dimensional uniform top-hat intensity optical and x-ray profiles.

Nutrient Requirements of Renibacterium salmoninarum on Agar and in Broth Media

In well-aerated broth cultures, good growth of Renibacterium salmoninarum was obtained in a serum-free medium consisting of 1% peptone, 1% yeast extract, and 0.1% l -cysteine (PYC broth). In contrast, serum or charcoal is required for growth on agar medium. Charcoal treatment of broth media, either before bacterial inoculation or during growth, increased the growth of R. salmoninarum , whereas the surfactants Tween 20 and Tween 80 inhibited growth. l -Cysteine was essential for optimal growth. Other organic sulfur compounds, such as d -cysteine, l -methionine, homocysteine, homocysteine thiolactone, and reduced glutathione, supported only lower levels of growth, while cystine and dithiothreitol did not allow growth.

Antibody specificities of polyclonal rabbit and rainbow trout antisera against Vibrio ordalii and serotype 0:2 strains of Vibrio anguillarum

Polyclonal rabbit antisera raised against Vibrio ordalii and serotype 02 strains of Vibrio anguillarum showed extensive cross-reactivity with lipopolysaccharide from these bacterial pathogens of fish when tested in western immunoblot analysis. Results with absorbed polyclonal antisera indicated that lipopolysaccharide molecules from these strains had both common and strain-specific antigenic determinants, which allowed the antisera to be used to differentiate between V. ordalii and serotype 02 strains of V. anguillarum. Unlike rabbits, the immune response in rainbow trout to serotype 02 common antigenic epitopes was dependent on the source of the immunizing lipopolysaccharide antigens. Serum from fish immunized with V. ordalii antigens reacted more extensively with serotype 02 common antigens. In contrast, fish anti-V. anguillarum 02 serum did not interact with O antigens from the V. ordalii strains. Lipopolysaccharide from V. anguillarum serotype 02 and 02a strains showed identical antibody binding properties when interacted with rabbit or fish antiserum to either V. anguillarum 02 or V. ordalii. Lipopolysaccharide from V. anguillarum 02b strains did not interact with the tested rabbit or fish polyclonal sera. The results from this study suggest that fish and rabbits recognise different antigenic determinants in lipopolysaccharide from V. ordalii and serotype 02 V. anguillarum strains; that V. ordalli and serotype 02 strains of V. anguillarum should be regarded as distinct serotype 02 subgroups based on the strain-specific antigenic determinants; and finally that the serological classification of V. anguillarum serotype 02b strains should be reexamined.

Characterization of the Renibacterium salmoninarum haemagglutinin

Water-extracted proteins from nine geographically diverse strains of Renibacterium salmoninarum, all of which agglutinated rabbit erythrocytes and rainbow trout spermatozoa, were compared by SDS-PAGE. Extracts from eight strains, including the type strain, ATCC 33209, were similar, containing a major protein of 57 kDa and a minor protein of 58 kDa. The SDS-PAGE protein profile of the Char strain did not contain the 58 kDa protein. A non-agglutinating strain, MT-239, which was also non-hydrophobic, did not produce any water-extractable protein. Immunoblot reactions with rabbit antiserum prepared against whole cells of the type strain demonstrated that the water-extracted haemagglutinins from the various strains were antigenically related. When purified by polyacrylamide gel zone electrophoresis, the haemagglutinin from R. salmoninarum ATCC 33209 formed a doublet band with molecular masses of 57 and 58 kDa, similar to the previously described F antigen. The water-extracted haemagglutinin agglutinated salmonid spermatozoa, was degraded by protease K and trypsin, and was shown to self-assemble onto the cell surface.

Restriction endonuclease fingerprinting analysis of Canadian isolates of Aeromonas salmonicida

Restriction endonuclease fingerprinting (REF) analysis was used to examine total cellular DNA prepared from 56 independent field isolates of the fish pathogen, Aeromonas salmonicida. DNA was digested singly with the restriction enzymes EcoRI and HindIII, and the resulting fragments separated by polyacrylamide gel electrophoresis and visualized by silver staining. The REF patterns of typical isolates of A. salmonicida subsp. salmonicida were distinct from those of A. hydrophila, A. salmonicida subsp. achromogenes, A. salmonicida subsp. masoucida, and atypical isolates of A. salmonicida subsp. salmonicida. Differences between strains of typical A. salmonicida subsp. salmonicida could also be distinguished. Canadian isolates examined could be assigned to 1 of 12 different groups (REF groups), with the majority of the isolates belonging to REF groups 1 and 5. REF group 1 strains were isolated from British Columbia and New Brunswick while REF group 5 isolates were found in Ontario. None of the European strains examined had REF patterns identical to those of Canadian isolates. Based on REF analysis, there was little genetic heterogeneity detected among 23 isolates from two short-term studies of naturally occurring infections. Several different REF groups were seen among A. salmonicida collected over a 10-year period from coho salmon from the Credit River. Consistent with earlier biochemical and hybridization studies, the REF data suggest that A. salmonicida is a clonal pathogen. REF analysis can, however, permit the identification of subgroups, which may be useful in epidemiological studies.

Tn5-induced protease-deficient strains of Aeromonas hydrophila with reduced virulence for fish

Protease-deficient strains of Aeromonas hydrophila TF7 were induced by transposon Tn5 mutagenesis, with Escherichia coli 1830(pJB4JI) as the Tn5 donor. The parent strain has the cell surface characteristics associated with virulence for fish, and as it produces a single metalloprotease, mutants could be distinguished by direct plating on brain-heart infusion skim milk agar. Mutants Pd-7 and Pd-10 still produced metalloprotease, but at reduced levels and only after prolonged incubation. The activities of other exoenzymes and hemolysin were unaffected, and the mutants autoagglutinated in broth, indicating that the cell surface characteristics of A. hydrophila TF7 had been retained. Unlike the parent strain, the mutants did not produce lesions or mortalities in rainbow trout (Salmo gairneri) when 5 X 10(6) CFU were injected intramuscularly. The bacterial cells were completely cleared from the site of the injection and the organs within 7 days. For 60-g rainbow trout held at 10 degrees C, the 50% lethal dose of Pd-10 was greater than 10(7) CFU, compared with 8.1 X 10(5) CFU for the parent strain. The mutants were significantly more susceptible than the parent strain to the bactericidal effect of fresh normal trout serum in vitro. Mutants Pd-7 and Pd-10 grew as well as the parent on M9 salts-glucose medium but more slowly on heat-inactivated fish serum. Thus, protease appears to be able to contribute to the establishment of A. hydrophila infection in fish both by overcoming initial host defenses and by providing nutrients for cell proliferation.

Experimental induction of the carrier state in yearling brook trout: a model challenge protocol for IPNV immunization

Brook trout fry (Salvelinus fontinalis) were not protected from infectious pancreatic necrosis virus (IPNV) challenge by immersion vaccination with inactivated, purified virus at concentrations of 10(7) to 10(9) pfu/ml. Mortalities in vaccinated groups were higher than for the unvaccinated control group and appeared to be dose-dependent. A challenge protocol for adult brook trout was developed for future vaccine trials. A single intraperitoneal injection of virulent, purified virus was sufficient to make long-lasting carriers of 16 month-old trout. Fish underwent a transient viremia, identified by virus isolation from plasma and leucocytes. Feces were the most reliable samples for identification of IPNV carriers by non-sacrificial testing. Many fish in the remaining infected group were still carriers 12 and 27 weeks post-infection.

Charcoal agar, a new growth medium for the fish disease bacterium Renibacterium salmoninarum

Charcoal is an effective replacement for serum in media for the isolation and culture of Renibacterium salmoninarum, the causative agent of bacterial kidney disease in salmonid fish. The medium, KDM-C, contains 10 g of peptone, 0.5 g of yeast extract, 1 g of L-cysteine hydrochloride, 1 g of activated charcoal, and 15 g of agar per liter and is adjusted to pH 6.8 with NaOH before autoclaving. Eight strains of R. salmoninarum grew from dilute inocula as well on KDM-C as on a standard serum-containing medium (KDM-2). The medium was effective for both primary isolations from fish and repeated transfers and has potential value for antigen preparation and physiological studies.

Antimicrobial susceptibility patterns and R plasmid-mediated resistance of the fish pathogen Yersinia ruckeri

Fifty strains of Yersinia ruckeri, the causative agent of enteric redmouth disease of salmonid fish, were tested for susceptibility to 23 antimicrobial agents by using an agar dilution procedure. The MICs were generally uniform for all serological varieties. Two of the 50 strains carried a 36-megadalton plasmid which determined resistance to tetracyclines and sulfonamides and was transferable to both Escherichia coli and Y. ruckeri recipients. The serovars did differ in their response to polymyxin B. Strains of serovars II, III, and V were highly resistant (MICs of 128 to 512 micrograms/ml), whereas most serovar I strains were susceptible to less than or equal to 2.0 micrograms/ml. Of 33 serovar I strains, 6 were highly resistant to polymyxin B, which is a characteristic that may divide serovar I (Hagerman) strains into two distinct subgroups.

Isolation of Yersinia ruckeri Bacteriophages

Eight bacteriophages effective against Yersinia ruckeri , the enteric redmouth disease bacterium, were isolated. Phage YerA41, a tailed icosahedral virus isolated from sewage enrichments, lysed 34 of 35 strains of Y. ruckeri serovar I, but was inactive against 15 strains belonging to three other serological groups. Six other phages lysed strains of serovars II, V, and I′, a subgroup of serovar I. YerL62, a phage obtained by mitomycin C induction, was specific for one of three serovar V strains. These bacteriophages, particularly YerA41, have potential value for fish disease diagnostic work.

Extracellular virulence factors of Aeromonas hydrophila in fish infections

Aeromonas hydrophila NRC 505 produced extracellular substances which were capable of causing pathological effects when injected into trout. Proteolytic activity and haemolytic activity of the extracellular products, and the effect on fish, were lost on heating. The extracellular substances from strain G35, a protease-deficient mutant, were significantly more toxic to both rainbow trout (Salmo gairdneri) and speckled trout (Salvelinus fontinalis) than the analogous preparation from the parental strain NRC 505. The response of speckled trout injected intraperitoneally with dilutions of the extracellular preparations implicates haemolytic activity as a significant lethality factor.

Amino acid uptake systems in Bacteroides ruminicola

Uptake of amino acids by Bacteroides ruminicola was observed in cells grown in a complete defined medium, containing ammonia as the nitrogen source. A high rate of uptake occurred only in fresh medium, as an inhibitory substance, possibly acetate, apparently accumulated during growth. All amino acids except proline were taken up and incorporated into cold trichloroacetic acid precipitable material. Different patterns of incorporation and different responses to 2,4-dinitrophenol and potassium ferricyanide indicated multiple uptake systems were involved. Kinetic inhibition patterns suggested six distinct systems were present for amino acid uptake, with specificities related to the chemical structures of the amino acids. Thus, the failure of free amino acids to act as sole nitrogen sources for growth of B. ruminicola is not due to the absence of transport systems for these compounds.

Possible regulation of nucleoside transport and RNA synthesis in Achlya

The transport systems for adenosine, guanosine, uridine, cytidine, and thymidine were analysed kinetically, physically, and for a possible system of regulation in the fungus Achlya. Transport of nucleosides was inhibited by metabolic energy uncouplers, 2,4-dinitrophenol, carbonylcyanide-p-chlorophenylhydrazone, citrate (which chelate cell wall membrane calcium ions), and N6-substituted adenines (cytokinins) which displace three highly polyphosphorylated dinucleosides (HS3, HS2, and HS1) from a phosphorylated proteoglycan (PPG) attached to the cell membrane. Neither citrate nor the substituted adenines (except the nucleoside forms) entered the cell within the short period of transport measurements. Transport of nucleic-acid bases, adenine, uracil, cytosine, and thymine was unaffected by these inhibitors of nucleoside transport. Nucleosides were probably transported without modification for they could be made to efflux unchanged after being concentrated inside the cell which was then poisoned with metabolic energy uncouplers. The optimum pH of transport for all nucleosides except guanosine was 6.5. Guanosine had two pH optima at 6.5 and 8.0. They (nucleosides) were transported optimally between 30 and 40 °C, except thymidine which used a much higher optimum-temperature transport system.Osmotically shocked Achlya cells do not transport nucleosides but they do transport nucleic-acid bases which are taken up by facilitated diffusion. Osmotic-shock treatment of cells released the membrane PPG with associated calcium ions and HS compounds. When the PPG and HS compounds were relaid on the membrane, nucleoside transport was resumed by the cells.These results suggest that nucleoside transport and the PPG–Ca(II)–HS complex may be linked and that concentrating the nucleosides in the cells is an energy-linked activity.