Microalgae: a green source of renewable H(2)

This article summarizes recent advances in the field of algal hydrogen production. Two fundamental approaches are being developed. One involves the temporal separation of the usually incompatible reactions of O(2) and H(2) production in green algae, and the second involves the use of classical genetics to increase the O(2) tolerance of the reversible hydrogenase enzyme. The economic and environmental impact of a renewable source of H(2) are also discussed.

Coming to America: multiple origins of New World geckos

Geckos in the Western Hemisphere provide an excellent model to study faunal assembly at a continental scale. We generated a time-calibrated phylogeny, including exemplars of all New World gecko genera, to produce a biogeographical scenario for the New World geckos. Patterns of New World gecko origins are consistent with almost every biogeographical scenario utilized by a terrestrial vertebrate with different New World lineages showing evidence of vicariance, dispersal via temporary land bridge, overseas dispersal or anthropogenic introductions. We also recovered a strong relationship between clade age and species diversity, with older New World lineages having more species than more recently arrived lineages. Our data provide the first phylogenetic hypothesis for all New World geckos and highlight the intricate origins and ongoing organization of continental faunas. The phylogenetic and biogeographical hypotheses presented here provide an historical framework to further pursue research on the diversification and assembly of the New World herpetofauna.

Platinized Chloroplasts: A Novel Photocatalytic Material

Colloidal platinum was prepared and precipitated directly onto photosynthetic thylakoid membranes from aqueous solution and entrapped on fiberglass filter paper. This composition of matter was capable of sustained simultaneous photoevolution of hydrogen and oxygen when irradiated at any wavelength in the chlorophyll absorption spectrum. Experimental data support the interpretation that part of the platinum metal catalyst is precipitated adjacent to the photosystem I reduction site of photosynthesis and that electron transfer occurs across the interface between photosystem I and the catalyst. Photoactivity of the material was dependent on the nature of the ionic species from which the platinum was precipitated. All photoactive samples were prepared from the hexachloroplatinate(IV) ion, whereas samples prepared by precipitation of the tetraammineplatinum(II) ion showed no hydrogen evolution activity and only transient oxygen activity. This system is among the simplest known for photosynthetically splitting water into molecular hydrogen and oxygen.

Nanoscale photosynthesis: photocatalytic production of hydrogen by platinized photosystem I reaction centers

A study of the photocatalytic production of molecular hydrogen from platinized photosystem I (PSI) reaction centers is reported. At pH 7 and room temperature metallic platinum was photoprecipitated at the reducing end of PSI according to the reaction, [PtCl6]2- + 4e- + hv-->Pt decreases + 6Cl-, where it interacted with photogenerated PSI electrons and catalyzed the evolution of molecular hydrogen. The reaction mixture included purified spinach PSI reaction centers, sodium ascorbate and spinach plastocyanin. Experimental data on real-time catalytic platinum formation as measured by the onset and rates of hydrogen photoevolution as a function of time are presented. The key objective of the experiments was demonstration of functional nanoscale surface metalization at the reducing end of isolated PSI by substituting negatively charged [PtCl6]2- for negatively charged ferredoxin, the naturally occurring water-soluble electron carrier in photosynthesis. The data are interpreted in terms of electrostatic interactions between [PtCl6]2- and the positively charged surface of psaD, the ferredoxin docking site situated at the stromal interface of the photosynthetic membrane and which is presumably retained in our PSI preparation. A discussion of the rates of hydrogen evolution in terms of the structural components of the various PSI preparations as well as of those of the intact thylakoid membranes is presented.

Cranberry juice constituents affect influenza virus adhesion and infectivity

Cranberry juice contains high molecular weight materials (NDM) that inhibit bacterial adhesion to host cells as well as the co-aggregation of many oral bacteria. Because of its broad-spectrum activity, we investigated NDM's potential for inhibiting influenza virus adhesion to cells, and subsequent infectivity. Hemagglutination (HA) of red blood cells (RBC) caused by representatives of both influenza virus A subtypes (H1N1)and H3N2) and the B type was inhibited by NDM at concentrations of 125 microg/ml or lower, which is at least 20-fold lower than that usually found in cranberry juice. A dose-response effect of NDM on HA was demonstrated. The infectivity of the A and B types was significantly reduced by preincubation with NDM (250 microg/ml), as reflected by the lack of cytopathic effect on Madine-Darby canine kidney (MDCK) cells and the lack of HA activity in the media of infected cells. The effect of NDM was also tested after A or B type viruses were allowed to adsorb to and penetrate the cells. Various levels of reduction in virus tissue culture infective dose TCID50 were observed. The effect was most pronounced when NDM was added several times to the infected MDCK cells. Our cumulative findings indicate that the inhibitory effect of NDM on influenza virus adhesion and infectivity may have a therapeutic potential.

A novel liposomal influenza vaccine (INFLUSOME-VAC) containing hemagglutinin-neuraminidase and IL-2 or GM-CSF induces protective anti-neuraminidase antibodies cross-reacting with a wide spectrum of influenza A viral strains

A liposomal influenza vaccine (INFLUSOME-VAC) was developed with the objective of overcoming the major drawbacks of the currently used influenza vaccines: their relatively low efficacy in certain high-risk groups (the elderly, infants, the immunosuppressed) and the need for annual immunization. INFLUSOME-VAC consists of liposomes containing the viral surface proteins hemagglutinin (HA) and neuraminidase (NA) derived from various influenza strains and IL-2 or GM-CSF, as an adjuvant. Vaccination of mice showed that, whereas conventional vaccines induced a low- and short-term response against HA and very low or no anti-NA response, INFLUSOME-VAC produced high titers of both anti-HA and anti-NA antibodies (Abs) in young and old mice that persisted for at least 6 months. Moreover, the anti-NA Abs efficiently cross-reacted with several N2 viral subtypes spanning 20 years, and such vaccines afforded partial protection against heterosubtypic viral infection.

The Photosynthetic Unit of Hydrogen Evolution

A study of the absolute photoproduction of hydrogen by autotrophically grown Chlorella vulgaris with single-turnover flashes of light indicates that (i) while the Emerson and Arnold photosynthetic unit has the value chlorophyll: oxygen approximately 1700 : 1, the hydrogen analog of this unit has the value chlorophyll: hydrogen approximately 1400 : 1, and (ii) whereas the yield of oxygen from dark-adapted algal cells is zero on the first flash and then undergoes damped oscillations of period 4 about the steady-state value, the corresponding yield of hydrogen is fixed at the steady-state value from the first flash onward. These observations suggest that in the molecular mechanism of photosynthetic hydrogen evolution (i) the light reaction is at least 60 percent as efficient as the corresponding oxygen evolution reaction as measured by the ability to utilize absorbed visible quanta, and (ii) there are no sequential, photoproduced, metastable intermediates as there are in the case of oxygen evolution. Therefore, a minimum of two reducing equivalents from two different photosystems must have access to a common pool in producing molecular hydrogen if these photosystems each produce one electron per single-turnover flash.

Stand-off tissue-based biosensors for the detection of chemical warfare agents using photosynthetic fluorescence induction

Tissue biosensors made from immobilized whole-cell photosynthetic microorganisms have been developed for the detection of airborne chemical warfare agents and simulants. The sensor read-out is based on well-known principles of fluorescence induction by living photosynthetic tissue. Like the cyanobacteria and algae from which they were constructed, the sensors are robust and mobile. The fluorescence signal from the sensors was stable after 40 days, storage and they can be launched or dropped into suspected danger zones. Commercially available hand-held fluorometric detector systems were used to measure Photosystem II (PSII) photochemical efficiency of green algae and cyanobacteria entrapped on filter paper disks. Toxic agents flowing in the gas stream through the sensors can alter the characteristic fluorescence induction curves with resultant changes in photochemical yields. Tabun (GA), sarin (GB), mustard agent, tributylamine (TBA) (a sarin stabilizer), and dibutyl sulfide (DBS) (a mustard agent analog) were tested. Upper threshold limits of detectability for GA, TBA, and DBS are reported. With additional research and development, these biosensors may find application in stand-off detection of chemical and perhaps biological warfare agents under real-world conditions.

Description of a new octoploid frog species (Anura: Pipidae: Xenopus) from the Democratic Republic of the Congo, with a discussion of the biogeography of African clawed frogs in the Albertine Rift

We describe a new octoploid species of African clawed frog (Xenopus) from the Lendu Plateau in the northern Albertine Rift of eastern Democratic Republic of the Congo. This species is the sister taxon of Xenopus vestitus (another octoploid), but is distinguished by a unique morphology, vocalization and molecular divergence in mitochondrial and autosomal DNA. Using a comprehensive genetic sample, we provide new information on the species ranges and intra-specific diversity of African clawed frogs from the Albertine Rift, including the details of a small range extension for the critically endangered Xenopus itombwensis and previously uncharacterized variation in Xenopus laevis. We also detail a new method for generating cytogenetic preparations in the field that can be stored at room temperature for up to 3 weeks. While extending our understanding of the extant diversity in the Albertine Rift, this new species highlights components of species diversity in ancestral African clawed frogs that are not represented by known extant descendants.

Energetic efficiency of hydrogen photoevolution by algal water splitting

Absolute thermodynamic efficiencies of conversion of light energy into chemical-free energy of molecular hydrogen by intact microalgae have been measured with an original physical measuring technique using a tin-oxide semiconducting gas sensor. Thin films of microalgae comprising of 5 to 20 cellular monolayers have been entrapped on filter paper, thereby constraining them in a well-defined circular geometry. Based on absolute light absorption of visible polychromatic illumination in the low-intensity region of the light saturation curve, conversion efficiencies of 6 to 24% have been obtained. These values are the highest ever measured for hydrogen evolution by green algae.

Molecular electronics of a single photosystem I reaction center: studies with scanning tunneling microscopy and spectroscopy

Thylakoids and photosystem I (PSI) reaction centers were imaged by scanning tunneling microscopy. The thylakoids were isolated from spinach chloroplasts, and PSI reaction centers were extracted from thylakoid membranes. Because thylakoids are relatively thick nonconductors, they were sputter-coated with Pd/Au before imaging. PSI photosynthetic centers and chemically platinized PSI were investigated without sputter-coating. They were mounted on flat gold substrates that had been treated with mercaptoacetic acid to help bind the proteins. With tunneling spectroscopy, the PSI centers displayed a semiconductor-like response with a band gap of 1.8 eV. Lightly platinized (platinized for 1 hr) centers displayed diode-like conduction that resulted in dramatic contrast changes between images taken with opposite bias voltages. The electronic properties of this system were stable under long-term storage.

Chemical platinization and its effect on excitation transfer dynamics and P700 photooxidation kinetics in isolated photosystem I

Isolated photosystem I (PSI) reaction center/core antenna complexes (PSI-40) were platinized by reduction of [PtCl6]2- at 20 degrees C and neutral pH. PSI particles were visualized directly on a gold surface by scanning tunneling microscopy (STM) before and after platinization. STM results showed that PSI particles were monomeric and roughly ellipsoidal with major and minor axes of 6 and 5 nm, respectively. Platinization deposited approximately 1000 platinum atoms on each PSI particle and made the average size significantly larger (9 x 7 nm). In addition to direct STM visualization, the presence of metallic platinum on the PSI complexes was detected by its effect of actinic shading and electrostatic shielding on P700 photooxidation and P700+ reduction. The reaction centers (P700) in both platinized and nonplatinized PSI-40 were photooxidized by light and reduced by ascorbate repeatedly, although at somewhat slower rates in platinized PSI because of the presence of platinum. The effect of platinization on excitation transfer and trapping dynamics was examined by measuring picosecond fluorescence decay kinetics in PSI-40. The fluorescence decay kinetics in both platinized and control samples can be described as a sum of three exponential components. The dominant (amplitude 0.98) and photochemically limited excitation lifetime remained the same (16 ps) before and after platinization. The excitation transfer and trapping in platinized PSI-40 was essentially as efficient as that in the control (without platinization) PSI. The platinization also did not affect the intermediate-lifetime (400-600 ps) and long-lifetime (> 2500 ps) components, which likely are related to intrinsic electron transport and to functionally uncoupled chlorophylls, respectively. The amplitudes of these two components were exceptionally small in both of the samples. These results provide direct evidence that although platinization dramatically alters the photocatalytic properties of PSI, it does not alter the intrinsic excitation dynamics and initial electron transfer reactions in PSI.

The role of carbon dioxide in light-activated hydrogen production by Chlamydomonas reinhardtii

Light-activated hydrogen and oxygen evolution as a function of CO2 concentration in helium were measured for the unicellular green alga Chlamydomonas reinhardtii. The concentrations were 58, 30, 0.8 and 0 ppm CO2. The objective of these experiments was to study the differential affinity of CO2/HCO 3 (-) for their respective Photosystem II and Calvin cycle binding sites vis-à-vis photoevolution of molecular oxygen and the competitive pathways of hydrogen photoevolution and CO2 photoassimilation. The maximum rate of hydrogen evolution occurred at 0.8 ppm CO2, whereas the maximum rate of oxygen evolution occurred at 58 ppm CO2. The key result of this work is that the rate of photosynthetic hydrogen evolution can be increased by, at least partially, satisfying the Photosystem II CO2/HCO 3 (-) binding site requirement without fully activating the Calvin-Benson CO2 reduction pathway. Data are presented which plot the rates of hydrogen and oxygen evolution as functions of atmospheric CO2 concentration in helium and light intensity. The stoichiometric ratio of hydrogen to oxygen changed from 0.1 at 58 ppm to approximately 2.5 at 0.8 ppm. A discussion of partitioning of photosynthetic reductant between the hydrogen/hydrogenase and Calvin-Benson cycle pathways is presented.

Local SIgA response following administration of a novel intranasal inactivated influenza virus vaccine in community residing elderly

Community-residing elderly were immunized twice intranasally three weeks apart with a new inactivated whole influenza vaccine. A control group was immunized intramuscularly with conventional influenza vaccine. Local antibody response was detected in about 50% of intranasally immunized subjects compared to about 20% of intramuscularly immunized subjects, to the three viral strains. Increasing the incidence of elevated IgA response may prevent influenza at its early stages thus reducing complications in the elderly.

Sexual differentiation in the spiny softshell turtle (Apalone spinifera), a species with genetic sex determination

It is hypothesized on the basis of sex determination theory that species exhibiting genetic sex determination (GSD) may undergo sexual differentiation earlier in development than species with environmental sex determination (ESD). Most turtle species exhibit a form of ESD known as temperature-dependent sex determination (TSD), and in such species the chronology of sex differentiation is well studied. Apalone spinifera is a species of softshell turtle (Trionychidae) that exhibits GSD. We studied sexual differentiation in this species in order to facilitate comparison to TSD species. Eggs were incubated at two different temperatures and embryos were harvested at various stages of mid to late development. Gonad length was measured with image analysis software, then prepared histologically. Indifferent gonads have differentiated in stage 19 embryos. Histological details of gonadogenesis follow the same pattern as described for other reptiles. Regression of the male paramesonephric duct closely follows testicular differentiation. Gonad lengths are longer at the warmer incubation temperature, and ovaries are generally longer than testes at each stage and for each temperature. Although sexual differentiation takes place at about the same stage as in other turtles with TSD (18-20), in A. spinifera this differentiation is irreversible at this stage, while in some of the TSD species sex is reversible until about stage 22. This immutable, definitive sexual differentiation may support the hypothesis of an accelerated chronology of sex differentiation for this species. We also note that sexual dichromatism at hatching is known in this species and may provide additional evidence of early differentiation. J. Exp. Zool. 290:190-200, 2001.

Oxygenic Photoautotrophic Growth Without Photosystem I

Contrary to the prediction of the Z-scheme model of photosynthesis, experiments demonstrated that mutants of Chlamydomonas containing photosystem II (PSII) but lacking photosystem I (PSI) can grow photoautotrophically with O2 evolution, using atmospheric CO2 as the sole carbon source. Autotrophic photosynthesis by PSI-deficient mutants was stable both under anaerobic conditions and in air (21 percent O2) at an actinic intensity of 200 microeinsteins per square meter per second. This PSII photosynthesis, which was sufficient to support cell development and mobility, may also occur in wild-type green algae and higher plants. The mutants can survive under 2000 microeinsteins per square meter per second with air, although they have less resistance to photoinhibition.

Photosynthetic hydrogen and oxygen production: kinetic studies

Steady-state turnover times for simultaneous photosynthetic production of hydrogen and oxygen have been measured for two systems: the in vitro system comprised of isolated chloroplasts, ferredoxin, and hydrogenase, and the anaerobically adapted green alga Chlamydomonas reinhardtii [137c(+) mating type]. In both systems, the simultaneous photoproduction of hydrogen and oxygen was measured by driving the systems into the steady state with repetitive, single-turnover, flash illumination. The turnover times for production of both oxygen and hydrogen in photosynthetic water splitting are in milliseconds and are equal to or less than the turnover time for carbon dioxide reduction in intact algal cells. The oxygen and hydrogen turnover times are therefore compatible with each other and partially compatible with the excitation rate of the photosynthetic reaction centers under conditions of solar irradiation.

Photoreduction of NADP + sensitized by synthetic pigment systems

Two synthetic pigment systems capable of enzymatically photoreducing NADP(+) are described. One system contains proflavine; the other, acridine. The complete system consists of ethylene diamine tetraacetic acid (EDTA), proflavine (or acridine), ferredoxin-NADP reductase (EC 1.6.99.4), and NADP(+). The two pigments initiate the photoreduction of NADP(+) in different portions of the electromagnetic spectrum. Proflavine photosensitizes in the visible portion; acridine, in the ultraviolet. Neither proflavine nor acridine is structurally related to chlorophyll. The acridine system has the attractive property that the enzyme, ferredoxin-NADP reductase, is the only component of the system that absorbs appreciably in the visible region of the spectrum.

A double-blind trial of a new inactivated, trivalent, intra-nasal anti-influenza vaccine in general practice: relationship between immunogenicity and respiratory morbidity over the winter of 1997-98

BACKGROUND

Influenza is responsible for considerable morbidity not only among older people but in younger age groups as well. However, most large-scale anti-influenza vaccination campaigns are still aimed principally at the elderly using injectable vaccines. Until now there has been much less emphasis on targeting younger populations or using intra-nasal vaccines in mass anti-influenza immunisation programmes.

OBJECTIVES

To assess the immunogenicity of a new inactivated intra-nasal anti-influenza vaccine and to measure its effect on respiratory morbidity in a volunteer general practice population.

STUDY DESIGN

A prospective, double-blind, placebo-controlled trial using the new vaccine was carried out over the winter of 1997-98 on 274 healthy patients aged 12-60 from three Israeli general practices, 182 in the vaccine group and 92 in the placebo group. Following vaccination the changes in the antigen levels and episodes of respiratory illness in the vaccine and placebo groups were measured.

RESULTS

Protective antibody levels occurred after a single dose of vaccine [influenza H1N1, 41% immune pre-vaccination to 73% post-vaccination; influenza H3N2, 35-66%; influenza B, 27-64%]. Between January and March 1998, when influenza activity was at a peak in Israel, the average number of respiratory illness events in the vaccine group [14 events/100 subjects per month] was significantly less than in the placebo group [22 events/100 subjects per month]; similarly, the average number of respiratory illness days in the vaccine group over the same period [69 days/100 subjects per month] was significantly less than in the placebo group [117 days/100 subjects per month].

CONCLUSIONS

The new vaccine possessed significant immunogenicity and was associated with a significant reduction in respiratory morbidity among a group of healthy older children and adults. Since intra-nasal vaccines are simpler to administer and more acceptable to the public than injections the vaccine's potential for use in routine anti-influenza vaccination campaigns seems promising, especially if its beneficial effects are also reproducible in more medically vulnerable populations.