Characterization of mannitol metabolism in the mangrove red algaCaloglossa leprieurii (Montagne) J.Agardh

A metabolic pathway, known as the mannitol cycle in fungi, has been identified as a new entity in the eulittoral mangrove red algaCaloglossa leprieurii (Montagne) J. Agardh. Three specific enzymes, mannitol-1-phosphate dehydrogenase (Mt1PDH; EC 1.1.1.17), mannitol-1-phosphatase (MtlPase; EC 3.1.3.22), mannitol dehydrogenase (MtDH; EC 1.1.1.67) and one nonspecific hexokinase (HK; EC 2.7.1.1) were determined and biochemically characterized in cell-free extracts. Mannitol-1-phosphate dehydrogenase showed activity maxima at pH 7.0 [fructose-6-phosphate (F6P) reduction] and pH 8.5 [oxidation of mannitol-1-phosphate (Mt1P)], and a very high specificity for both carbohydrate substrates. TheK _m values were 1.4 mM for F6P, 0.09 mM for MOP, 0.020 mM for NADH and 0.023 mM for NAD⁺. For the dephosphorylation of MOP, MtlPase exhibited a pH optimum at 7.2, aK _m value of 1.2 mM and a high requirement of Mg²⁺ for activation. Mannitol dehydrogenase had activity maxima at pH 7.0 (fructose reduction) and pH 9.8 (mannitol oxidation), and was less substrate-specific than Mt1PDH and MtlPase, i.e. it also catalyzed reactions in the oxidative direction with arabitol (64.9%), sorbitol (31%) and xylitol (24.8%). This enzyme showedK _m values of 39 mM for fructose, 7.9 mM for mannitol, 0.14 mM for NADH and 0.075 mM for NAD⁺. For the non-specific HK, only theK _m values for fructose (0.19 mM) and glucose (7.5 mM) were determined. The activities of the anabolic enzymes Mt1PDH and MtlPase were always at least two orders of magnitude higher than those of the degradative enzymes, indicating a net carbon flow towards a high intracellular mannitol pool. The function of mannitol metabolism inC. leprieurii as a biochemical adaptation to the environmental extremes in the mangrove habitat is discussed.Abbreviations F6P fructose-6-phosphate - HK hexokinase - Mt1P mannitol-1-phosphate - Mt1PDH mannitol-1-phosphate dehydrogenase - Mt1Pase mannitol-1-phosphatase - MtDH mannitol dehydrogenase     

Statistic evaluation of the influence of species variation,culture conditions,surface wettability and fluid shear on attachment and biofilm development of marine bacteria

A budding coccoid bacterium, (CH1), a Vibrio sp. and a Pseudomonas sp. were investigated for factors governing their attachment to glass surfaces in static batch culture and laminar flow continuous culture systems. An analysis of variance showed that the three species exhibited very different responses. For CH1 attachment was dependent on cell density, incubation time and nutrient concentration. The Vibrio sp. was affected by nutrient concentration while the attachment of the Pseudomonas sp. was independent of cell density, incubation time and nutrient concentration. A comparison of attachment to hydrophilic and hydrophobic surfaces showed that attachment of the Vibrio sp. and CH1 to hydrophilic surfaces was 3 and 10 times greater respectively than to hydrophobic surfaces while Pseudomonas attached in equal numbers to both surfaces. The continuous culture system with defined flow hydrodynamics and growth conditions at steady state revealed a random sampling effect 3 times smaller than the batch culture system did. When the biofilm development of Pseudomonas sp. was followed during 46 h at different fluid shear under laminar and turbulent flow conditions, the former biofilm reached 3.3·10⁸ cells·cm^-2 and the latter 8.2·10⁷ cells·cm^-2.Non-common abbreviation NSS Nine salt solution     

Photosynthetic water oxidation: The protein framework

Approximately 20 protein subunits are associated with the PS II complex, not counting subunits of peripheral light-harvesting antenna complexes. However, it is not yet established which proteins specifically are involved in the water-oxidation process. Much evidence supports the concept that the D1/D2 reaction center heterodimer not only plays a central role in the primary photochemistry of Photosystem II, but also is involved in electron donation to P680 and in ligation of the manganese cluster. This evidence includes (a) the primary donor to P680 has been shown to be a redox-active tyrosyl residue (Tyr161) in the D1 protein, and (b) site-directed mutagenesis and computer-assisted modeling of the reaction center heterodimer have suggested several sites with a possible function in manganese ligation. These include Asp170, Gln165 and Gln189 of the D1 protein and Glu69 of the D2 protein as well as the C-terminal portion of the mature D1 protein. Also, hydrophilic loops of the chlorophyll-binding protein CP43 that are exposed at the inner thylakoid surface could be essential for the water-splitting process.In photosynthetic eukaryotes, three lumenal extrinsic proteins, PS II-O (33 kDa), PS II-P (23 kDa) and PS II-Q (16 kDa), influence the properties of the manganese cluster without being involved in the actual catalysis of water oxidation. The extrinsic proteins together may have multiple binding sites to the integral portion of PS II, which could be provided by the D1/D2 heterodimer and CP47. A major role for the PS II-O protein is to stabilize the manganese cluster. Most experimental evidence favors a connection of the PS II-P protein with binding of the Cl^- and Ca²⁺ ions required for the water oxidation, while the PS II-Q protein seems to be associated only with the Cl^- requirement. The two latter proteins are not present in PS II of prokaryotic organisms, where their functions may be replaced by a 10–12 kDa subunit and a newly discovered low-potential cytochrome c-550.Abbreviations PS II Photosystem II - PCC Pasteur Culture Collection     

The elimination of fox rabies from Europe: determinants of success and lessons for the future

Despite perceived challenges to controlling an infectious disease in wildlife, oral rabies vaccination (ORV) of foxes has proved a remarkably successful tool and a prime example of a sophisticated strategy to eliminate disease from wildlife reservoirs. During the past three decades, the implementation of ORV programmes in 24 countries has led to the elimination of fox-mediated rabies from vast areas of Western and Central Europe. In this study, we evaluated the efficiency of 22 European ORV programmes between 1978 and 2010. During this period an area of almost 1.9 million km² was targeted at least once with vaccine baits, with control taking between 5 and 26 years depending upon the country. We examined factors influencing effort required both to control and eliminate fox rabies as well as cost-related issues of these programmes. The proportion of land area ever affected by rabies and an index capturing the size and overlap of successive ORV campaigns were identified as factors having statistically significant effects on the number of campaigns required to both control and eliminate rabies. Repeat comprehensive campaigns that are wholly overlapping much more rapidly eliminate infection and are less costly in the long term. Disproportionally greater effort is required in the final phase of an ORV programme, with a median of 11 additional campaigns required to eliminate disease once incidence has been reduced by 90 per cent. If successive ORV campaigns span the entire affected area, rabies will be eliminated more rapidly than if campaigns are implemented in a less comprehensive manner, therefore reducing ORV expenditure in the longer term. These findings should help improve the planning and implementation of ORV programmes, and facilitate future decision-making by veterinary authorities and policy-makers.     

The virtual ecologist approach: simulating data and observers

Ecologists carry a well‐stocked toolbox with a great variety of sampling methods, statistical analyses and modelling tools, and new methods are constantly appearing. Evaluation and optimisation of these methods is crucial to guide methodological choices. Simulating error‐free data or taking high‐quality data to qualify methods is common practice. Here, we emphasise the methodology of the ‘virtual ecologist’ (VE) approach where simulated data and observer models are used to mimic real species and how they are ‘virtually’ observed. This virtual data is then subjected to statistical analyses and modelling, and the results are evaluated against the ‘true’ simulated data. The VE approach is an intuitive and powerful evaluation framework that allows a quality assessment of sampling protocols, analyses and modelling tools. It works under controlled conditions as well as under consideration of confounding factors such as animal movement and biased observer behaviour. In this review, we promote the approach as a rigorous research tool, and demonstrate its capabilities and practical relevance. We explore past uses of VE in different ecological research fields, where it mainly has been used to test and improve sampling regimes as well as for testing and comparing models, for example species distribution models. We discuss its benefits as well as potential limitations, and provide some practical considerations for designing VE studies. Finally, research fields are identified for which the approach could be useful in the future. We conclude that VE could foster the integration of theoretical and empirical work and stimulate work that goes far beyond sampling methods, leading to new questions, theories, and better mechanistic understanding of ecological systems.     

Getting to guanine: mechanism and dynamics of charge separation and charge recombination in DNA revisited.

The mechanism and dynamics of charge separation and charge recombination in synthetic DNA hairpins possessing a stilbenedicarboxamide linker and a single guanine-cytosine base pair have been reinvestigated. The combination of femtosecond broad-band pump probe spectroscopy, nanosecond transient absorption experiments, and picosecond fluorescence decay measurements permits analysis of the formation and decay of the stilbene anion radical. Reversible hole injection resulting in the formation of the stilbene-adenine contact radical ion pair is found to occur on the picosecond time scale. The mechanism for charge separation across two or more base pairs is revised from single step superexchange to a multi-step process: hole injection followed by hole transport and hole trapping. The mechanism of charge recombination remains assigned to a superexchange process.