Molecular microbiology and pathogenesis of Helicobacter and Campylobacter updated: a meeting report of the 11th conference on Campylobacter,Helicobacter and related organisms

The genome analysis of the gastrointestinal pathogens Helicobacter and Campylobacter has stimulated a wealth of new research activities, which are presented every 2 years at the international conferences on Campylobacter, Helicobacter and Related Organisms (CHRO). Both organisms represent excellent models for the identification of new molecular mechanisms involved in pathogenesis, host response and physiological adaptation in course of acute and chronic infectious diseases. The investigation of their global distribution, pronounced genetic and antigenic diversity as well as the molecular mechanisms allowing long-term persistence in hostile and unusual microbial habitats, is a challenge for scientists of many different disciplines world-wide. With a focus on the molecular microbiology aspects, this review summarizes recent trends in Helicobacter and Campylobacter research by highlighting selected presentations at the 11th CHRO conference. The topics include the discovery of new virulence factors, functional analysis of protein secretion systems, host signalling pathways, adaptation to stress conditions, global gene regulation, and genetic variability.     

Photosynthetic acclimation of Tradescantia albiflora to growth irradiance: morphological, ultrastructural and growth responses

Tradescantia albiflora (Kunth), a trailing ground species naturally occurring in deep shade in rainforests, has an unusual photosynthetic acclimation profile for growth irradiance. Although capable of increasing its capacity for electron transport, photophosphorylation and carbon fixation when grown in full sunlight, Tradescantia has constant chlorophyll alb ratios, photosystem reaction centre stoichiometry and pigment-protein composition at all growth irradiances (Chow et al. 1991. Physiol. Plant. 81: 175–182). To gain an insight into the compensatory strategies which allow Tradescantia to grow in both high and low lights, plants were grown under shade cloth (100 to 1.4% relative growth irradiance) and leaf and chloroplast attributes were compared. While shade Tradescantia chloroplasts had three times more chlorophyll per chloroplast and twice the length of thylakoid membranes compared to plants grown in full sunlight, the ratios of appressed to nonappressed thylakoid membranes were constant. The average net surface charge density of destacked thylakoids was the same for plants grown at moderate and low-irradiance, consistent with their similar stacking profiles. Tradescantia plants grown in direct sunlight had 10-times more fresh and dry weight per plant compared to plants grown in shade, despite a lower photosynthetic capacity on a leaf area basis with partial photoinhibition. We conclude that having a light-harvesting apparatus permanently locked into the "shade-plant mode " does not necessarily prevent a plant from thriving in high light. Analyses of leaf growth at different irradiances provide a partial explanation of the manner in which Tradescantia compensates for very low photosynthetic capacity per unit leaf in sunlight.     

Effects of Two Potential Allelochemicals on the Photosystem II of <i>Nitzschia closterium</i> and<i> Monostroma nitidum</i>

In aquaculture, high-density seaweed farming brings higher economic benefits but also increases outbreaks of diatom felt. The effective control of diatom felt in high-density seaweed farming has always been a research hotspot. This study selected two potential allelochemicals 2-hydroxycinnamic acid and quinic acid to explore their effects on a diatom Nitzschia closterium and an economic seaweed Monostroma nitidum. The results showed that 2-hydroxycinnamic acid had better inhibitory effects than quinic acid on the growth, pigment content and photosynthetic efficiency of N. closterium. Their half-maximal inhibitory concentrations at 120 h (IC_{50–120 h}) were 0.9000 and 1.278 mM, respectively. Additionally, these allelochemicals had limited inhibitory effects on the growth, pigment content and photosynthetic efficiency of M. nitidum before 24 h. To further explore the allelopathic effect of these chemicals, this study focused on the photosystem II energy fluxes of N. closterium. It was found that 3 mM 2-hydroxycinnamic acid could destroy the whole photosynthetic system by devastating the PSII reaction centre (RC) before 24 h; however, the same concentration of quinic acid could only down-regulate the electron transport efficiency by changing the effective antenna size of an active RC and downregulating the PSII reaction centre density. These experimental results are expected to provide a new strategy to control diatom felt blooms on the high-density seaweed farming areas.     

Properties of Photosynthetic Mutants Isolated from Euglena gracilis

Four different photosynthetic mutants of Euglena gracilis were characterized as to their lesions in photosynthetic electron transport. Two were defective around photosystem II: one, in electron transport on the oxidizing side of photosystem II, and the second lacked cytochrome 558. The location of the defect in the third mutant was concluded to be in the carbon fixation cycle, since it could catalyse both photosynthetic electron transport and photophosphorylation. The fourth mutant had a defect in its mechanism of photophosphorylation.     

Directed evolution and in silico analysis of reaction centre proteins reveal molecular signatures of photosynthesis adaptation to radiation pressure

Evolutionary mechanisms adopted by the photosynthetic apparatus to modifications in the Earth's atmosphere on a geological time-scale remain a focus of intense research. The photosynthetic machinery has had to cope with continuously changing environmental conditions and particularly with the complex ionizing radiation emitted by solar flares. The photosynthetic D1 protein, being the site of electron tunneling-mediated charge separation and solar energy transduction, is a hot spot for the generation of radiation-induced radical injuries. We explored the possibility to produce D1 variants tolerant to ionizing radiation in Chlamydomonas reinhardtii and clarified the effect of radiation-induced oxidative damage on the photosynthetic proteins evolution. In vitro directed evolution strategies targeted at the D1 protein were adopted to create libraries of chlamydomonas random mutants, subsequently selected by exposures to radical-generating proton or neutron sources. The common trend observed in the D1 aminoacidic substitutions was the replacement of less polar by more polar amino acids. The applied selection pressure forced replacement of residues more sensitive to oxidative damage with less sensitive ones, suggesting that ionizing radiation may have been one of the driving forces in the evolution of the eukaryotic photosynthetic apparatus. A set of the identified aminoacidic substitutions, close to the secondary plastoquinone binding niche and oxygen evolving complex, were introduced by site-directed mutagenesis in un-transformed strains, and their sensitivity to free radicals attack analyzed. Mutants displayed reduced electron transport efficiency in physiological conditions, and increased photosynthetic performance stability and oxygen evolution capacity in stressful high-light conditions. Finally, comparative in silico analyses of D1 aminoacidic sequences of organisms differently located in the evolution chain, revealed a higher ratio of residues more sensitive to oxidative damage in the eukaryotic/cyanobacterial proteins compared to their bacterial orthologs. These results led us to hypothesize an archaean atmosphere less challenging in terms of ionizing radiation than the present one.     

The golden age of biochemical research in photosynthesis

The perspectives and enthusiasms recorded in this review describe the events I witnessed and, in small ways, contributed to. Two great rewards emerged from my experiences – the pleasure of doing experiments and the great wealth of friendships with students and colleagues. As a graduate student, phenomena appeared at the bench before me which clarified the coupling of electron transport to ATP synthesis. My first PhD graduate student measured concentrations of pyridine nucleotides in chloroplasts and his results have been often confirmed and well used. All of the many graduate students who followed contributed to our understanding of photosynthesis. I have taken much pleasure from documenting the details of photosynthetic phosphorylation and electron transport in cyanobacteria. Studies of the `c' type cytochromes in these organisms continue to fascinate me. My experiences in government in its efforts to promote research are unusual, perhaps unique. A rare event outside the laboratory – a natural bloom of cyanobacteria – stimulated new thoughts and special opportunities for laboratory science. Photosynthesis seems magisterial in its shaping of our planet and its biology and in the details of its cleverness that were revealed in the time of my witness. This revised version was published online in June 2006 with corrections to the Cover Date.     

Nitrogen-fixing symbiosis between photosynthetic bacteria and legumes

Rhizobia having photosynthetic systems form nitrogen-fixing nodules on the stem and/or root of some species of the legumes Aeschynomene and Lotononis. This review is focused on the recent knowledge about the physiology, genetics and role of the photosystem in these bacteria. Photosynthetic electron transport seems to involve reaction centers, soluble cytochrome c2 and cytochrome bc1. Anaerobically, the electron transport system becomes over-reduced. The photosynthesis genes have been partially characterized; their organization is classical but their regulation is unusual as it is activated by far-red light via a bacteriophytochrome. This original mechanism of regulation seems well adapted to promote photosynthesis during stem symbiosis. Photosynthesis plays a major role in the efficiency of stem nodulation. It is also observed that infrared light stimulates nitrogen fixation in nodules containing photosynthetic bacteroids, suggesting that photosynthesis may additionally provides energy for nitrogen fixation, allowing for more efficient plant growth. Other aspects of these bacteria are discussed, in particular their taxonomic position and nodulation ability, the role of carotenoids and the potential for application of photosynthetic rhizobia in rice culture. This revised version was published online in June 2006 with corrections to the Cover Date.     

Structural basis for the oxidation of thiosulfate by a sulfur cycle enzyme

Reduced inorganic sulfur compounds are utilized by many bacteria as electron donors to photosynthetic or respiratory electron transport chains. This metabolism is a key component of the biogeochemical sulfur cycle. The SoxAX protein is a heterodimeric c-type cytochrome involved in thiosulfate oxidation. The crystal structures of SoxAX from the photosynthetic bacterium Rhodovulum sulfidophilum have been solved at 1.75 A resolution in the oxidized state and at 1.5 A resolution in the dithionite-reduced state, providing the first structural insights into the enzymatic oxidation of thiosulfate. The SoxAX active site contains a haem with unprecedented cysteine persulfide (cysteine sulfane) coordination. This unusual post-translational modification is also seen in sulfurtransferases such as rhodanese. Intriguingly, this enzyme shares further active site characteristics with SoxAX such as an adjacent conserved arginine residue and a strongly positive electrostatic potential. These similarities have allowed us to suggest a catalytic mechanism for enzymatic thiosulfate oxidation. The atomic coordinates and experimental structure factors have been deposited in the PDB with the accession codes 1H31, 1H32 and 1H33.     

Primary and new production in the deep Canada Basin during summer 2002

The NOAA Ocean Exploration program provided the opportunity to measure the carbon and nitrogen productivity across the Canada Basin. This research examined the major environmental factors limiting the levels of primary production and possible future climate change on the ecosystems. The vertical distributions of the carbon and nitrogen uptakes of phytoplankton had similar patterns as their respective biomass concentrations which were low at the surface and highest in the chlorophyll-maximum layer. The annual carbon and new production rates of phytoplankton in the Canada Basin were about 5 and 1 g C m^–2, respectively. Nutrients were determined to be a main limiting factor at the surface, whereas light may be a major factor limiting phytoplankton productivity in the chlorophyll-maximum layer for open waters. The bottom surface of the ice has a low specific uptake and productivity of phytoplankton, indicating that photosynthetic activity might be controlled by both light and nutrients.     

The energy source for CO<Subscript>2</Subscript> transport in the marine microalga <Emphasis Type="Italic">Nannochloris atomus</Emphasis>

CO2 fluxes in the marine microalga Nannochloris atomus were studied by mass spectrometry using inhibitors and artificial acceptors of photosynthetic electron transport to investigate the energy source for CO2 uptake. This algal species is capable of taking up CO2 from the external medium by active transport but lacks active HCO(3)(-) transport and extracellular carbonic anhydrase. The capacity of cells to take up CO2 was a function of photosynthetic photon flux density. Dark respiration rates were also dependent upon the light intensity during the preceding illumination period, indicating the presence of light-enhanced dark respiration. Addition of 3-(3',4'-dichlorophenyl)-1,1-dimethylurea to illuminated cell suspensions that had been allowed to concentrate inorganic carbon internally during photosynthesis caused a rapid burst of CO2, demonstrating that active CO2 transport had been abolished. A similar response was obtained when cell suspensions were treated with 2,5-dibromo-6-isopropyl-3methyl-1,4-benzoqinone or hydroxylamine. When methyl viologen was used to drain electrons from ferredoxin, cells were still able to take up CO2 from the external medium, although C-fixation decreased with time. These results demonstrate that active CO2 transport in N. atomus is supported by photosynthetic linear electron transport.     

A New Screening Method for Algal Photosynthetic Mutants (CO2-Insensitive Mutants of the Green Alga Chlorella ellipsoidea)

A new method has been developed for screening algal photosynthetic mutants. This method uses autoradiography to assess gross photosynthetic 14C fixation by green algal colonies on agar plates and allows the identification of clones that differ in photosynthetic characteristics from wild-type cells. Three wild-type cells, high-CO2-grown Chlorella ellipsoidea, air-grown C. ellipsoidea, and air-grown Chlorella saccharophila, had K0.5 values for dissolved inorganic carbon (DIC) of 1083, 250, and 50 [mu]M, respectively, and as plaques on agar plates at Chl densities greater than 25 [mu]g cm-2 exhibited relative amounts of 14C fixation of 15, 55, and 100%, respectively. Cells of C. ellipsoidea were mutagenized with x-rays and screened by this method. Growth of C. ellipsoidea in high CO2 represses DIC transport and thus lowers its affinity for DIC. Five of the mutants detected by this method showed high-affinity photosynthesis similar to air-grown wild-type cells even when grown in high CO2. Seven other mutants when grown in high CO2 showed affinities for DIC intermediate between air-grown and high-CO2-grown wild-type cells. The affinities of high-CO2-grown mutants were reflected precisely in their capacities to accumulate DIC intracellularly. These results indicate that the mutants are fully or partially insensitive to the repressive effect of ambient CO2 concentration on DIC transport.     

A novel type of monoheme cytochrome c: biochemical and structural characterization at 1.23 A resolution of rhodothermus marinus cytochrome c

Monoheme cytochromes of the C-type are involved in a large number of electron transfer processes, which play an essential role in multiple pathways, such as respiratory chains, either aerobic or anaerobic, and the photosynthetic electron transport chains. This study reports the biochemical characterization and the crystallographic structure, at 1.23 A resolution, of a monoheme cytochrome c from the thermohalophilic bacterium Rhodothermus marinus. In addition to an alpha-helical core folded around the heme, common for this type of cytochrome, the X-ray structure reveals one unusual alpha-helix and a unique N-terminal extension, which wraps around the back of the molecule. Based on a thorough structural and amino acid sequence comparison, we propose R. marinus cytochrome c as the first characterized member of a new class of C-type cytochromes.     

Seaside transportation—from structure to function of translocation machines

The EMBO conference ‘From Structure to Function of Translocation Machines’ took place in April 2013 in Dubrovnik, Croatia. The meeting brought together a mix of established and aspiring researchers to discuss a wealth of unpublished data and ideas in a lively scientific programme of talks designed to shatter the established dogma. From new ways to envisage known protein transport pathways to a brand new and totally unconventional protein transport system, surprises were part and parcel of this excellent EMBO conference.     

Biodelivery of a fullerene derivative

Most current nanotoxicology research is focused on examining the influence of nanomaterials at the tissue and cellular levels. To explore these interactions on the molecular level, new carboxyfullerenes interact with transport proteins at the molecular level. The carboxyfullerenes exhibited an unusual mode of binding outside the calyx of beta-lactoglobulin (a typical representative of lipocalin family of barrier liquid proteins). The complexes were studied by various techniques, including mass spectrometry, UV/vis and circular dichroism spectroscopy, chromatographic methods, gel electrophoresis, and dynamic light scattering. The fullerene ligands were transferred from beta-lactoglobulin to human serum albumin (a representative of a blood transport protein), thus providing a model of how fullerene-based nanomaterials interact with biomolecules and are transported in biological systems.     

几种蓝藻光合NAD（P）H脱氢酶复合体研究的新进展

蓝藻NAD（P）H脱氢酶（NDH-1）是一种重要的光合膜蛋白复合体,参与CO2吸收、围绕光系统I的循环电子传递和细胞呼吸。就几种蓝藻NDH-1复合体的鉴定、结构、生理功能等研究的新进展进行了综述与分析,并对今后NDH-1复合体的研究作了展望。     

Minor antenna proteins CP24 and CP26 affect the interactions between photosystem II subunits and the electron transport rate in grana membranes of Arabidopsis

We investigated the function of chlorophyll a/b binding antenna proteins Chlorophyll Protein 26 (CP26) and CP24 in light harvesting and regulation of photosynthesis by isolating Arabidopsis thaliana knockout lines that completely lacked one or both of these proteins. All three mutant lines had a decreased efficiency of energy transfer from trimeric light-harvesting complex II (LHCII) to the reaction center of photosystem II (PSII) due to the physical disconnection of LHCII from PSII and formation of PSII reaction center depleted domains in grana partitions. Photosynthesis was affected in plants lacking CP24 but not in plants lacking CP26: the former mutant had decreased electron transport rates, a lower DeltapH gradient across the grana membranes, reduced capacity for nonphotochemical quenching, and limited growth. Furthermore, the PSII particles of these plants were organized in unusual two-dimensional arrays in the grana membranes. Surprisingly, overall electron transport, nonphotochemical quenching, and growth of the double mutant were restored to wild type. Fluorescence induction kinetics and electron transport measurements at selected steps of the photosynthetic chain suggested that limitation in electron transport was due to restricted electron transport between Q(A) and Q(B), which retards plastoquinone diffusion. We conclude that CP24 absence alters PSII organization and consequently limits plastoquinone diffusion.     

Coping with branch excision when measuring leaf net photosynthetic rates in a lowland tropical forest

Measuring leaf gas exchange from canopy leaves is fundamental for our understanding of photosynthesis and for a realistic representation of carbon uptake in vegetation models. Since canopy leaves are often difficult to reach, especially in tropical forests with emergent trees up to 60 m at remote places, canopy access techniques such as canopy cranes or towers have facilitated photosynthetic measurements. These structures are expensive and therefore not very common. As an alternative, branches are often cut to enable leaf gas exchange measurements. The effect of branch excision on leaf gas exchange rates should be minimized and quantified to evaluate possible bias. We compared light-saturated leaf net photosynthetic rates measured on excised and intact branches. We selected branches positioned at three canopy positions, estimated relative to the top of the canopy: upper sunlit foliage, middle canopy foliage, and lower canopy foliage. We studied the variation of the effects of branch excision and transport among branches at these different heights in the canopy. After excision and transport, light-saturated leaf net photosynthetic rates were close to zero for most leaves due to stomatal closure. However, when the branch had acclimated to its new environmental conditions—which took on average 20 min—light-saturated leaf net photosynthetic rates did not significantly differ between the excised and intact branches. We therefore conclude that branch excision does not affect the measurement of light-saturated leaf net photosynthesis, provided that the branch is recut under water and is allowed sufficient time to acclimate to its new environmental conditions.     

Is electron transport to oxygen an important mechanism in photoprotection? Contrasting responses from Antarctic vascular plants

Photoreduction of oxygen by the photosynthetic electron transport chain has been suggested to be an important process in protecting leaves from excess light under conditions of stress; however, there is little evidence that this process occurs significantly except when plants are exposed to conditions outside their normal tolerance range. We have examined the oxygen dependency of photosynthetic electron transport in the two vascular plants found growing in Antarctica – Colobanthus quitensis and Deschampsia antarctica. Photosynthetic electron transport in C. quitensis is insensitive to changes in oxygen concentration under non-photorespiratory conditions, indicating that electron transport to oxygen is negligible; however, it has a substantial capacity for non-photochemical quenching (NPQ) of chlorophyll fluorescence. In contrast, D. antarctica has up to 30% of its photosynthetic electron transport being linked to oxygen, but has a substantially lower capacity for NPQ. Thus, these plants rely on contrasting photoprotective mechanisms to cope with the Antarctic environment. Both plants seem to use cyclic electron flow associated with PSI, however, this is activated at a lower irradiance in C. quitensis than in D. antarctica.     

Different phycobilin antenna organisations affect the balance between light use and growth rate in the cyanobacterium Microcystis aeruginosa and in the cryptophyte Cryptomonas ovata

During the recent years, wide varieties of methodologies have been developed up to the level of commercial use to measure photosynthetic electron transport by modulated chlorophyll a-in vivo fluorescence. It is now widely accepted that the ratio between electron transport rates and new biomass (P (Fl)/B (C)) is not fixed and depends on many factors that are also taxonomically variable. In this study, the balance between photon absorption and biomass production has been measured in two phycobilin-containing phototrophs, namely, a cyanobacterium and a cryptophyte, which differ in their antenna organization. It is demonstrated that the different antenna organization exerts influence on the regulation of the primary photosynthetic reaction and the dissipation of excessively absorbed radiation. Although, growth rates and the quantum efficiency of biomass production of both phototrophs were comparable, the ratio P (Fl)/B (C) was twice as high in the cryptophyte in comparison to the cyanobacterium. It is assumed that this discrepancy is because of differences in the metabolic regulation of cell growth. In the cryptophyte, absorbed photosynthetic energy is used to convert assimilated carbon directly into proteins and lipids, whereas in the cyanobacterium, the photosynthetic energy is preferentially stored as carbohydrates.