Search

Cyanobacteria play essential roles in marine primary productivity and the global carbon/nitrogen biogeochemical cycle. Increasing urea emissions and decreasing pH value in the ocean caused by human activities are changing the community structure and competitive interactions of marine phytoplankton, which will have a profound impact on the marine ecosystem and global biogeochemical cycle. Here, we report that a coastalSynechococcusstrain exhibited better adaptability to extreme low pH conditions when it uses urea as nitrogen source compared to using other inorganic nitrogen. Very low pH values can also alleviate damage by high concentrations of urea to cyanobacteria. Urease plays an essential role in this process.Synechococcusmutants with inactivated urease cannot adapt well to highly acidic environments, while heterologous expression of urease homologs from acidophilicHelicobacter pylorican help the cyanobacterial mutants to restore their adaptability to acidification. A TARA Oceans database analysis indicates that the distribution of cyanobacteria with the urease gene is closely related to estuaries and nearshore waters with potentially high urea inputs. In summary, we report for the first time that the use of urea and adaptation to acid stress are highly interactive in marine phytoplankton. Future work should determine whether this interaction is likely to allow phytoplankton that utilize urea to have a competitive advantage in the future ocean with high urea emissions and environmentally relevant pH scenarios.

Marine cyanobacteria contribute to approximately half of the ocean primary production, and their biomass is limited by low iron (Fe) bioavailability in many regions of the open seas. The mechanisms by which marine cyanobacteria overcome Fe limitation remain unclear. In this study, multiple Fe uptake pathways have been identified in a coastal strain of Synechococcus sp. strain PCC 7002. A total of 49 mutants were obtained by gene knockout methods, and 10 mutants were found to have significantly decreased growth rates compared to the wild type (WT). The genes related to active Fe transport pathways such as TonB-dependent transporters and the synthesis and secretion of siderophores are found to be essential for the adaptation of Fe limitation in Synechococcus sp. PCC 7002. By comparing the Fe uptake pathways of this coastal strain with other open-ocean cyanobacterial strains, it can be concluded that the Fe uptake strategies from different cyanobacteria have a strong relationship with the Fe bioavailability in their habitats. The evolution and adaptation of cyanobacterial iron acquisition strategies with the change of iron environments from ancient oceans to modern oceans are discussed. This study provides new insights into the diversified strategies of marine cyanobacteria in different habitats from temporal and spatial scales. IMPORTANCE Iron (Fe) is an important limiting factor of marine primary productivity. Cyanobacteria, the oldest photosynthetic oxygen-evolving organisms on the earth, play crucial roles in marine primary productivity, especially in the oligotrophic ocean. How they overcome Fe limitation during the long-term evolution process has not been fully revealed. Fe uptake mechanisms of cyanobacteria have been partially studied in freshwater cyanobacteria but are largely unknown in marine cyanobacterial species. In this paper, the characteristics of Fe uptake mechanisms in a coastal model cyanobacterium, Synechococcus sp. PCC 7002, were studied. Furthermore, the relationship between Fe uptake strategies and Fe environments of cyanobacterial habitats has been revealed from temporal and spatial scales, which provides a good case for marine microorganisms adapting to changes in the marine environment.

Cyanobacteria are globally important primary producers and nitrogen fixers with high iron demands. Low ambient dissolved iron concentrations in many aquatic environments mean that these organisms must maintain sufficient and selective transport of iron into the cell. However, the nature of iron transport pathways through the cyanobacterial outer membrane remains obscure. Here we present multiple lines of experimental evidence that collectively support the existence of a novel class of substrate-selective iron porin, Slr1908, in the outer membrane of the cyanobacterium Synechocystis sp. PCC 6803. Elemental composition analysis and short-term iron uptake assays with mutants in Slr1908 reveal that this protein is primarily involved in inorganic iron uptake and contributes less to the accumulation of other metals. Homologues of Slr1908 are widely distributed in both freshwater and marine cyanobacteria, most notably in unicellular marine diazotrophs. Complementary experiments with a homologue of Slr1908 in Synechococcus sp. PCC 7002 restored the phenotype of Synechocystis knockdown mutants, showing that this siderophore producing species also possesses a porin with a similar function in Fe transport. The involvement of a substrate-selective porins in iron uptake may allow cyanobacteria to tightly control iron flux into the cell, particularly in environments where iron concentrations fluctuate.

The stretch stress of each layer of laminate composite undergoes complex changes after being stretched, which significantly affects the stretch strength. In order to determine the magnitude of the change, the paper directly solved the stretch stress using the analytical method through simple assumptions, and obtained the analytical calculation formula. Studies on double-layer plates show that the magnitude of stretch stress is closely related to the elastic modulus, length and thickness dimensions of the plate layer, the shear modulus of the adhesive, the thickness of the adhesive layer, and the external stress, and the maximum stress occurs at the middle section. The calculation of the formula provides a convenient way to check the stretch strength.

In order to improve the management of nitrogen (N) fertilization in pear orchards, we investigated the effects of application timing on the distribution, storage, and remobilization of N in mature pear trees in a field experiment at Jingtai County, Gansu Province, China. Nine trees were selected for the experiment and each received equal aliquots of 83.33 g N in the autumn, spring, and summer, with 15N-labeled (NH4)2SO4 used in one of the aliquots each season. Results showed that the (15N H4)2SO4 applied in the autumn remained in the soil during the winter. In the following spring this N was absorbed and rapidly remobilized into each organ, especially new organs (leaves, fruit and new shoots). The 15N supplied in spring was rapidly transported to developing fruit between the young fruit and fruit enlargement stages. 15N from the summer application of fertilizer was mainly stored in the coarse roots over the winter, then was mobilized to support growth of new organs in spring. In conclusion, for pear trees we recommend that the autumn application of N-fertilizer be soon after fruit harvest in order to increase N stores in fine roots. Spring application should be between full bloom and the young fruit stages to meet the high N demands of developing fruit. Summer application of fertilizer at the fruit enlargement stage does not contemporaneously affect the growth of pears, but increases the N stored in coarse roots, and in turn the amount available for remobilization in spring.

Global warming will be combined with predicted increases in thermal variability in the future surface ocean, but how temperature dynamics will affect phytoplankton biology and biogeochemistry is largely unknown. Here, we examine the responses of the globally important marine coccolithophore Emiliania huxleyi to thermal variations at two frequencies (one-day and two-day) at low (18.5 °C) and high (25.5 °C) mean temperatures. Elevated temperature and thermal variation decreased growth, calcification and physiological rates, both individually and interactively. One-day thermal variation frequencies were less inhibitory than two-day variations under high temperature, indicating that high frequency thermal fluctuations may reduce heat‐induced mortality and mitigate some impacts of extreme high temperature events. Cellular elemental composition and calcification was significantly affected by both thermal variation treatments relative to each other, and to the constant temperature controls. The negative effects of thermal variation on E. huxleyi growth rate and physiology are especially pronounced at high temperatures. These responses of the key marine calcifier E. huxleyi to warmer, more variable temperature regimes have potentially large implications for ocean productivity and marine biogeochemical cycles under a future changing climate.

We present a class of two-dimensional memristive maps with a cosine memristor. The memristive maps do not have any fixed points, so they belong to the category of nonlinear maps with hidden attractors. The rich dynamical behaviors of these maps are studied and investigated using different numerical tools, including phase portrait, basins of attraction, bifurcation diagram, and Lyapunov exponents. The two-parameter bifurcation analysis of the memristive map is carried out to reveal the bifurcation mechanism of its dynamical behaviors. Based on our extensive simulation studies, the proposed memristive maps can produce hidden periodic, chaotic, and hyper-chaotic attractors, exhibiting extremely hidden multi-stability, namely the coexistence of infinite hidden attractors, which was rarely observed in memristive maps. Potentially, this work can be used for some real applications in secure communication, such as data and image encryptions.

The cyanobacterium Nostoc flagelliforme is an extremophile that thrives under extraordinary desiccation and ultraviolet (UV) radiation conditions. To investigate its survival strategies, we performed whole-genome sequencing of N. flagelliforme CCNUN1 and transcriptional profiling of its field populations upon rehydration in BG11 medium. The genome of N. flagelliforme is 10.23 Mb in size and contains 10 825 predicted protein-encoding genes, making it one of the largest complete genomes of cyanobacteria reported to date. Comparative genomics analysis among 20 cyanobacterial strains revealed that genes related to DNA replication, recombination and repair had disproportionately high contributions to the genome expansion. The ability of N. flagelliforme to thrive under extreme abiotic stresses is supported by the acquisition of genes involved in the protection of photosynthetic apparatus, the formation of monounsaturated fatty acids, responses to UV radiation, and a peculiar role of ornithine metabolism. Transcriptome analysis revealed a distinct acclimation strategy to rehydration, including the strong constitutive expression of genes encoding photosystem I assembly factors and the involvement of post-transcriptional control mechanisms of photosynthetic resuscitation. Our results provide insights into the adaptive mechanisms of subaerial cyanobacteria in their harsh habitats and have important implications to understand the evolutionary transition of cyanobacteria from aquatic environments to terrestrial ecosystems.

Atmospheric haze pollution is a popular environmental issue in recent years. The aerosols reduce solar radiation reaching land surface, with consequences on the growth of crops. In order to examine the effects of low solar radiation intensity on the physiological characteristics and mineral nutrition of grain crops, the random designed field experiment of rice cultivar 'Nanjing 5055' planted under different shading degrees (CK, natural sunlight control; Y近年来雾霾等大气环境污染问题突出,气溶胶导致到达地表的太阳辐射强度降低,对农作物生长造成了较大影响。为了探讨太阳辐射强度降低对粮食作物生理特性和矿质元素营养的影响,本研究以‘南粳5055’水稻品种为供试材料,采用田间随机区组设计,通过不同程度遮光处理模拟弱光环境(CK,不遮光对照;Y

This paper studies a new class of two-dimensional rational maps exhibiting self-excited and hidden attractors. The mathematical model of these maps is firstly formulated by introducing a rational term. The analysis of existence and stability of the fixed points in these maps suggests that there are four types of fixed points, i.e., no fixed point, one single fixed point, two fixed points and a line of fixed points. To investigate the complex dynamics of these rational maps with different types of fixed points, numerical analysis tools, such as time histories, phase portraits, basins of attraction, Lyapunov exponent spectrum, Lyapunov (Kaplan–Yorke) dimension and bifurcation diagrams, are employed. Our extensive numerical simulations identify both self-excited and hidden attractors, which were rarely reported in the literature. Therefore, the multi-stability of these maps, especially the hidden one, is further explored in the present work.

In oligotrophic oceans, low bioavailability of Fe is a key factor limiting primary productivity. However, excessive Fe in cells leads to the Fenton reaction, which is toxic to cells. Cyanobacteria must strictly maintain intracellular Fe homeostasis. Here, we knocked out a series of genes encoding efflux systems in Synechocystis sp. PCC 6803, and found eight genes that are required for high Fe detoxification. Unexpectedly, the HlyBD-TolC efflux system plays an important role in the adaptation of Synechocystis under Fe-deficient conditions. Mutants of HlyD and TolC grew worse than the wild-type strain under low-Fe conditions and showed significantly lower intracellular Fe contents than the wild-type strain. We excluded the possibility that the low Fe sensitivity of the HlyBD-TolC mutants was caused by a loss of the S-layer, the main extracellular protein secreted via this efflux system. Inactivation of the HlyD protein influenced type IV pili formation and direct inactivation of type IV pili related genes affected the adaptation to low-Fe conditions. HlyBD-TolC system is likely involved in the formation of type IV pili and indirectly influenced Fe acquisition. Our findings suggest that efflux system in non-siderophore-producing cyanobacteria can facilitate Fe uptake and help cells adapt to Fe-deficient conditions via novel pathways.

BackgroundHIV testing and early linkage to care are critical for reducing the risk of HIV transmission. HIV self-testing (HIVST) is an useful tool for increasing HIV testing frequency.This study aimed to investigate HIVST rates among men who have sex with men (MSM), the characteristics of MSM who had HIVST, and factors associated with HIVST uptake among MSM in Ningbo, China. MethodsA cross-sectional study was conducted from April to October 2019 in Ningbo,China. Participants were aged at least 18 years and having had sexual contact with men in the past year. Proportions were used for categorical variables. Adjusted Odds Ratio (AOR) and 95% Confidence Interval (CI) for characteristics associated with HIVST uptake was processed by multiple logistic regression models.ResultsAmong a sample of 699 MSM recruited, 38.2% had reported previous use of an HIV self-test kit. A greater proportion of HIVST Users had a higher frequency of HIV testing(≥2 times: 70.0% versus 41.2%, pConclusionsFurther HIVST education should be strengthened for school-aged children and teenagers, and free HIVST kits may be provided to low-income high-risk MSM through gay apps and NGOs to achieve the increased HIV testing frequency.

Cyanobacteria are the oldest oxygen-evolving photosynthetic organisms on the Earth. They are widely distributed in marine, freshwater, and terrestrial environments and contribute about 25% of global primary productivity. They are thought to be responsible for the conversion of the Earth’s atmosphere from anaerobic to aerobic about 2.4 billion years ago. This development permitted the evolution of aerobic bacteria, algae, plants, and animals. However, due to the emergence of oxidative environments on the Earth’s surface, soluble ferrous iron (Fe2+) was almost completely oxidized to hardly soluble ferric iron (Fe3+) in aquatic environments. The extremely low bioavailability of iron in the ocean has been considered as an important factor that is limiting global primary productivity. As photosynthetic organisms, cyanobacteria have higher iron demand than other non-photosynthetic organisms to meet the needs of photosynthetic electron transport and chlorophyll synthesis. The nitrogen-fixing cyanobacteria need even more iron to fix the inert dinitrogen gas. The contradiction between the high iron demand of cyanobacteria and their iron-limiting habitats has forced them to evolve special strategies to overcome iron deficiency during the long-period evolution. In this review, we summarized the recent perspectives on the physiological responses and special strategies of cyanobacteria to overcome the changing iron bioavailability in freshwater, coastal, and open-ocean environments.

The cyanobacterium Trichodesmium fixes as much as half of the nitrogen (N2) that supports tropical open-ocean biomes, but its growth is frequently limited by iron (Fe) availability1,2. How future ocean warming may interact with this globally widespread Fe limitation of Trichodesmium N2 fixation is unclear3. Here, we show that the optimum growth temperature of Fe-limited Trichodesmium is ~5 °C higher than for Fe-replete cells, which results in large increases in growth and N2 fixation under the projected warmer Fe-deplete sea surface conditions. Concurrently, the cellular Fe content decreases as temperature rises. Together, these two trends result in thermally driven increases of ~470% in Fe-limited cellular iron use efficiencies (IUEs), defined as the molar quantity of N2 fixed by Trichodesmium per unit time per mole of cellular Fe (mol N2 fixed h–1 mol Fe–1), which enables Trichodesmium to much more efficiently leverage the scarce available Fe supplies to support N2 fixation. Modelling these results in the context of the IPCC representative concentration pathway (RCP) 8.5 global warming scenario4 predicts that IUEs of N2 fixers could increase by ~76% by 2100, and largely alleviate the prevailing Fe limitation across broad expanses of the tropical Pacific and Indian Oceans. Thermally enhanced cyanobacterial IUEs could increase future global marine N2 fixation by ~22% over the next century, and thus profoundly alter the biology and biogeochemistry of open-ocean ecosystems. The growth of nitrogen-fixing marine cyanobacteria Trichodesmium is limited by iron availability under current conditions. However warmer temperatures reduce the iron requirement, allowing greater growth rates and increased nitrogen fixation.

Objective: To study the effect of Xuebijing, thymopentin combined with symptomatic treatment on inflammatory response process in elderly patients with severe pneumonia. Methods: A total of 60 elderly patients with severe pneumonia who were treated in the hospital between August 2014 and July 2016 were collected and divided into control group and observation group according to the random number table, 30 cases in each group. Control group received clinical symptomatic treatment, and observation group received Xuebijing, thymopentin combined with symptomatic treatment. The differences in serum proinflammatory factors, anti-inflammatory factors as well as liver and kidney function indexes were compared between the two groups before and after treatment. Results: Before treatment, differences in serum levels of pro-inflammatory factors, anti-inflammatory factors as well as liver and kidney function indexes were not statistically significant between the two groups. After treatment, serum IL-1β, IL-6, IL-8, IL-4, IL-13, TB, ALT, AKP, Scr and CysC levels of both groups of patients were lower than those before treatment, and serum IL-1β, IL-6, IL-8, IL-4, IL-13, TB, ALT, AKP, Scr and CysC levels of observation group were lower than those of control group. Conclusion: Xuebijing, thymopentin combined with symptomatic treatment can effectively inhibit the degree of systemic inflammatory response and reduce the liver and kidney function injury in elderly patients with severe pneumonia.

The structural behavior of precast concrete segmental bridges (PCSBs) is affected by the joints between the concrete segments. In this study, a numerical model was established to investigate the direct shear behavior of single-keyed dry joints in PCSBs. The numerical model was validated by the full-scale test results published by the authors. It was found that the numerical results of the joints, such as the ultimate shear load, cracking pattern, and load-displacement curves, matched the test results well. The validated numerical model was further used for extending parametric studies. The factors affecting the shear behavior of single-keyed dry joints include the confining pressure, concrete strength, and key depth. It was found that the ultimate shear capacity increased about 121% when the confining pressure increased from 0.1 to 3.0 MPa, it was very low under confining pressure of 0.1 MPa; it increased about 44% when the concrete strength increased from C40 to C100; it increased about 203% when the key depth increased from 15 to 40 mm. However, the ultimate shear capacity decreased about 20% when the key depth increased from 40 to 60 mm, hence 40 mm was recommended for the design depth of the single-keyed dry joints in PCSBs. Finally, the parametric analysis results were compared with the AASHTO specification. When the key depth was 35, 40 and 45 mm, the AASHTO specification conservatively predict the shear strength capacity of single-keyed dry joints.

Ultraviolet-B radiation is known to harm most photosynthetic organisms with the exception of several studies of photosynthetic eukaryotes in which UV-B showed positive effects. In this study, we investigated the effect of acclimation to low UV-B radiation on growth and photosynthesis of the cyanobacterium Nostoc sphaeroides. Exposure to 0.08 W m-2 UV-B plus low visible light for 14 d significantly increased the growth rate and biomass production by 16% and 30%, respectively, compared with those under visible light alone. The UV-B acclimated cells showed an approximately 50% increase in photosynthetic efficiency (α) and photosynthetic capacity (Pmax ), a higher PSI/PSII fluorescence ratio, an increase in PSI content and consequently enhanced cyclic electron flow, relative to those of non-acclimated cells. Both the primary quinone-type acceptor and plastoquinone pool re-oxidation were up-regulated in the UV-B acclimated cells. In parallel, the UV-B acclimated colonies maintained a higher rate of D1 protein synthesis following exposure to elevated intensity of UV-B or visible light, thus functionally mitigating photoinhibition. The present data provide novel insight into photosynthetic acclimation to low UV-B radiation and suggest that UV-B may act as a positive ecological factor for the productivity of some photosynthetic prokaryotes, especially during twilight periods or in shaded environments.

Retinoblastoma (RB) is a common neoplasm that is exhibited in individuals globally. Increasing evidence demonstrated that cyclin-dependent kinase regulatory subunit 1B (CKS1B) may be involved in the pathogenesis of various tumor types, including multiple myeloma and breast cancer. In the present study, the hypothesis that CKS1B down-regulation would effectively inhibit the proliferation, invasion and angiogenesis of RB cells through the mitogen-activated protein kinase kinase (MEK)/extracellular signal-regulated kinase (ERK) signaling pathway was examined. Initial investigation of the expression profile of CKS1B in RB and adjacent retina tissues was performed using reverse transcription-quantitative polymerase chain reaction and western blot analysis. A total of three RB cell lines, SO-RB50, Y79 and HXO-RB44, were examined for selection of the cell line with the highest expression of CKS1B, and human normal retinal vascular endothelial cells (ACBRI-181) were also evaluated. CKS1B short hairpin RNA (shRNA) sequences (shRNA CKS1B-1, shRNA CKS1B-2 and shRNA CKS1B-3) and negative control shRNA sequences were constructed and transfected into cells at the third generation to evaluate the role of shCKS1B and the MEK/ERK signaling pathway in RB. Furthermore, the effect of shCKS1B on cell proliferation, migration, invasion, apoptosis and angiogenesis was investigated. CKS1B was determined to be highly expressed in RB tissue, compared with adjacent retina tissue. SO-RB50 and HXO-RB44 cells treated with shRNA CKS1B-1 and shRNA CKS1B-2 were selected for the present experiments. Activation of the MEK/ERK signaling pathway increases the expression of MEK, ERK, B-cell lymphoma 2, proliferating cell nuclear antigen, cyclin D1, vascular endothelia growth factor and basic fibroblast growth factor, enhances cell proliferation, migration, invasion and lumen formation, and decreases apoptosis. Following silencing CKS1B, the aforementioned conditions were reversed. The key observations of the present study demonstrated that shCKS1B can inhibit the proliferation, invasion and angiogenesis of RB cells by suppressing the MEK/ERK signaling pathway. Thus, CKS1B represents a potential research target in the development of therapeutics for RB.

Cyanobacteria are globally important primary producers and abundant in some iron-limited ocean environments. The ways in which they take up iron are largely unknown, but reduction of Fe3+ is an important step in the process. Here we report a special iron permease in Synechocystis, cFTR1, that is required for Fe3+ uptake following Fe2+ re-oxidation. The expression of cFTR1 is induced by iron starvation, and a mutant lacking the gene is abnormally sensitive to iron starvation. The cFTR1 protein localizes to the plasma-membrane and contains the iron-binding motif “REXXE”. Point-directed mutagenesis of the REXXE motif results in a Fe-transport deficient phenotype. Measurements of iron (55Fe) uptake rate show that cFTR1 takes up Fe3+ but Fe2+. The function of cFTR1 in Synechocystis could be genetically complemented by the iron permease, Ftr1p, of Saccharomyces cerevisiae, that is known to transport Fe3+ produced by the oxidation of Fe2+ by a multi-copper oxidase. Unlike yeast Ftr1p, cyanobacterial cFTR1 probably obtains Fe3+ primarily from the oxidation of Fe2+ by oxygen. Growth assays show that the cFTR1 is required during oxygenic, photoautotrophic growth but not when oxygen production is inhibited during photoheterotrophic growth. In cyanobacteria, iron reduction/re-oxidation uptake pathway represents important adaptations of cyanobacteria in oxygenated environments. This article is protected by copyright. All rights reserved.

The cyanobacterium Nostoc flagelliforme is an extremophile that thrives under extraordinary desiccation and ultraviolet (UV) radiation conditions. To investigate its survival strategies, we performed whole-genome sequencing of N. flagelliforme CCNUN1 and transcriptional profiling of its field populations upon rehydration in BG11 medium. The genome of N. flagelliforme is 10.23 Mb in size and contains 10 825 predicted protein-encoding genes, making it one of the largest complete genomes of cyanobacteria reported to date. Comparative genomics analysis among 20 cyanobacterial strains revealed that genes related to DNA replication, recombination and repair had disproportionately high contributions to the genome expansion. The ability of N. flagelliforme to thrive under extreme abiotic stresses is supported by the acquisition of genes involved in the protection of photosynthetic apparatus, the formation of monounsaturated fatty acids, responses to UV radiation, and a peculiar role of ornithine metabolism. Transcriptome analysis revealed a distinct acclimation strategy to rehydration, including the strong constitutive expression of genes encoding photosystem I assembly factors and the involvement of post-transcriptional control mechanisms of photosynthetic resuscitation. Our results provide insights into the adaptive mechanisms of subaerial cyanobacteria in their harsh habitats and have important implications to understand the evolutionary transition of cyanobacteria from aquatic environments to terrestrial ecosystems.

Cyanobacteria are foundational drivers of global nutrient cycling, with high intracellular iron (Fe) requirements. Fe is found at extremely low concentrations in aquatic systems, however, and the ways in which cyanobacteria take up Fe are largely unknown, especially the initial step in Fe transport across the outer membrane. Here, we identified one TonB protein and four TonB-dependent transporters (TBDTs) of the energy-requiring Fe acquisition system and six porins of the passive diffusion Fe uptake system in the model cyanobacterium Synechocystis sp. strain PCC 6803. The results experimentally demonstrated that TBDTs not only participated in organic ferri-siderophore uptake but also in inorganic free Fe (Fe′) acquisition. (55)Fe uptake rate measurements showed that a TBDT quadruple mutant acquired Fe at a lower rate than the wild type and lost nearly all ability to take up ferri-siderophores, indicating that TBDTs are critical for siderophore uptake. However, the mutant retained the ability to take up Fe′ at 42% of the wild-type Fe′ uptake rate, suggesting additional pathways of Fe′ acquisition besides TBDTs, likely by porins. Mutations in four of the six porin-encoding genes produced a low-Fe-sensitive phenotype, while a mutation in all six genes was lethal to cell survival. These diverse outer membrane Fe uptake pathways reflect cyanobacterial evolution and adaptation under a range of Fe regimes across aquatic systems. IMPORTANCE Cyanobacteria are globally important primary producers and contribute about 25% of global CO(2) fixation. Low Fe bioavailability in surface waters is thought to limit the primary productivity in as much as 40% of the global ocean. The Fe acquisition strategies that cyanobacteria have evolved to overcome Fe deficiency remain poorly characterized. We experimentally characterized the key players and the cooperative work mode of two Fe uptake pathways, including an active uptake pathway and a passive diffusion pathway in the model cyanobacterium Synechocystis sp. PCC 6803. Our finding proved that cyanobacteria use ferri-siderophore transporters to take up Fe′, and they shed light on the adaptive mechanisms of cyanobacteria to cope with widespread Fe deficiency across aquatic environments.

FeOCl nanosheet arrays were deposited on fluorine-doped tin oxide glass substrates through a chemical vapor deposition method and further converted to hematite porous nanosheet arrays. A much enhanced photocurrent was obtained for such hematite films, which was three times higher than that of a planar hematite film at 1.23 V versus a reversible hydrogen reference electrode.

Iron availability has been suggested to be one of the key factors limiting the formation of Microcystis sp. blooms in eutrophic lakes. However, the significance of competition of Microcystis sp. with other phytoplankton species under iron limitation is still unclear. Here, the competitive ability of Microcystis aeruginosa is reported from mixed cultures with Pseudanabaena sp. or Chlorella pyrenoidosa at two iron concentrations (pFe 21.4 and 20.3). In monoculture, low iron conditions caused a smaller decrease in maximal relative electron transport rate, PSI/PSII fluorescence ratio and phycocyanin content in M. aeruginosa than in Pseudanabaena sp. The same iron concentration resulted in a significant decrease in chlorophyll a content, PSI/PSII fluorescence ratio, and maximal PSII photochemical yield in M. aeruginosa but there was no change in these factors in C. pyrenoidosa. All three species were more vulnerable to photoinhibition under low iron conditions. Iron limitation also decreased their cellular vol...

The lift coefficient of any wind turbine must have highest limit. In this paper, an analytical expression of lift coefficient associated with tip-speed ratio and lift-drag ratio of airfoil of wind turbine with ideal chord has been deduced by integrating along the blade wingspan using the blade element - momentum theory, which can be used for pre-estimating lift coefficient of actual wind turbine in design. Further, considering ideal fluid environment ( the drag coefficient is close to 0 ), an expression of the highest performance of lift only associated with tip-speed ratio has been deduced too, which is the highest boundary of lift coefficient of any actual wind turbine with same tip-speed ratio. The results show that for the wind turbine in steady state, there is a theoretical limit of the lift coefficient, 0.57795, which is the highest boundary that any actual wind turbine can not be crossed; if the tip-speed ratio is greater than 6 and lift-drag ratio less than 200, the lift coefficient is unlikely to exceed 0.2.

The sulfur-formation ( suf ) genes play important roles in both photosynthesis and respiration of cyanobacteria, but the organism prioritizes Fe–S clusters for respiration at the expense of photosynthesis. Iron–sulfur (Fe–S) clusters are important to all living organisms, but their assembly mechanism is poorly understood in photosynthetic organisms. Unlike non-photosynthetic bacteria that rely on the iron–sulfur cluster system, Synechocystis sp. PCC 6803 uses the Sulfur-Formation (SUF) system as its major Fe–S cluster assembly pathway. The co-expression of suf genes and the direct interactions among SUF subunits indicate that Fe–S assembly is a complex process in which no suf genes can be knocked out completely. In this study, we developed a condition-controlled SUF Knockdown mutant by inserting the petE promoter, which is regulated by Cu2+ concentration, in front of the suf operon. Limited amount of the SUF system resulted in decreased chlorophyll contents and photosystem activities, and a lower PSI/PSII ratio. Unexpectedly, increased cyclic electron transport and a decreased dark respiration rate were only observed under photoautotrophic growth conditions. No visible effects on the phenotype of SUF Knockdown mutant were observed under heterotrophic culture conditions. The phylogenetic distribution of the SUF system indicates that it has a co-evolutionary relationship with photosynthetic energy storing pathways.

This paper proposed a calculation model of transverse Poisson's ratio of continuous fiber reinforced composite, in which the fibers are centrally arranged in a representative volume element. According to the equivalent strain rule of matrix and fiber in fiber direction, the formula of transverse Poisson's ratio was deduced by mathematical method, which shows that the transverse Poisson's ratio of the composite material is associated with the Poisson's ratios and the elastic modulus of fiber and matrix. It was shown by an example that the transverse Poisson's ratio of composite was less than the weighted average number of the Poisson's ratios of fiber and matrix , even less than the matrix Poisson's ratio in a large range. The minimum value indicates that the fibers obviously resist longitudinal deformation under the transverse force.

Blade tip losses would reduce lift and power of wind turbine. This paper analyzed the mechanism of tip losses, and according to Prandtl and Glauert tip loss correction factor and blade element - momentum theory derived the blade chord formula with tip losses. Further, lift coefficient calculation formula was obtained by integrating along the blade span. The lift coefficient formula considering tip loss expressed the highest value of lift coefficient of any practical wind turbine with tip losses. The research shows, the impacts of tip losses to chord concentrated in the tip area; tip losses will reduce the lift coefficient about 2 to 6 percent when tip speed ratio changes from 10 to 4.

To improve the anti-wear properties of Mg alloys, Al-13Si, Al-15Si and Al-19Si coatings were prepared by supersonic particles deposition on the surface of ZM5 magnesium alloy. Micro-structure and anti-wear properties of the coatings were examined by digital micro-hardness tester, XRD, friction and abrasion testing machine, three-dimensional microscope and SEM. The results show that the wear-resistant layer and the magnesium substrate can be well integrated as mechanical bonding and the main wear failure mechanism of the three coatings is adhesive wear. Moreover, the micro-hardness of Al-19Si coating is 141.47HV0.05, much higher than Al-13Si coating (134.97HV0.05) and Al-15Si coating (136.02HV0.05). Besides, the anti-wear properties of Al-19Si coating is optimal, superior to Al-15Si coating and Al-13Si coating. All of those indicate that Al-19Si coating can provide the most excellent anti-wear protection for ZM5 magnesium alloy.

Electronic structures of semiconductor photocatalysts control the light absorbance, charge-carrier separation and mobility, activation energy and consequently, photocatalytic activity. Ion doping has been widely used to modify the electronic structure of a semiconductor photocatalyst. Here, we successfully synthesized Sn doped single crystalline anatase TiO2 particles dominated with {1 0 5} facets by a gas phase oxidation process, and their structure and composition were thoroughly analyzed by XRD/TEM/FESEM/XPS. The photoluminescence emission spectra measurements reveal that the small amount of doped Sn in TiO2 could suppress the recombination of photogenerated electron–hole pairs. Thus, the Sn doped TiO2 shows a significantly enhanced photocatalytic hydrogen evolution performance, with its hydrogen generation rate being 4.5 times higher than that of pure TiO2. First-principle simulation results suggest the doped Sn at the edge exhibit higher adsorption energy toward H, which could promote the H2 generation from the splitting of water.

Over the past decades, there have been many synthesis methods on producing well-defined crystals, due to their enormous application potentials in industrial field. Among them, high temperature gas-phase reactions (HTGR) approach may be one of the most promising processes for fabrication of well-defined crystals with controllable structure, size, shape, and composition. This review is focused on the recent progresses in synthesizing well-defined crystalline TiO2 dominated with, respectively, {001} facets and {105} facets, one-dimensional ZnO and SnO2 nanorods/nanowires, MoS2 nanosheets as well as GaP, InP, and GaAs nanowires via HTGR approach. Although these research works were currently carried out on experimental scale, it is worth to note that the industrial importance of this HTGR approach for design and fabrication of well-defined crystals in the future owing to its advantages of continuous and scalable production with controlled dimensions and low cost.

In this paper, when Reynolds number is within the range of 10000 to 1000000, the horizontal component of the total pressure of flow around flat plate at high angle of attack was regarded as lift of high angle of attack, and the vertical component was regarded as drag of high angle of attack. The horizontal component of total pressure at small angle of attack was regarded as shape drag, and the total drag coefficient at small angle of attack was considered to the sum of the shape drag and frictional drag at zero angle of attack. For the two states of large and small angle of attack, the application scopes of the formulas of lift and drag coefficients were given. Final, the relations of lift and drag coefficients were obtained by eliminating all angles of attack. Research results show that lift - drag curve of small angles of attack is parabola, and the lift - drag curve of high angles of attack is circle.

Photocatalytic hydrogen production from water or organic compounds is a promising way to resolve our energy crisis and environmental problems in the near future. Over the past decades, many photocatalysts have been developed for solar water splitting. However, most of these photocatalysts require cocatalyst to facilitate H2 evolution reaction and noble metals as key cocatalysts are widely used. Consequently, the condition of noble metal cocatalyst including the size and valence state etc plays the key role in such photocatalytic system. Here, the size and valence state effect of Pt on photocatalytic H2 evolution over platinized TiO2 photocatalyst were studied for the first time. Surprisingly, it was found that Pt particle size does not affect the photoreaction rate with the size range of several nanometers in this work, while it is mainly depended on the valence state of Pt particles. Typically, TOFs of TiO2 photodeposited with 0.1–0.2 wt% Pt can exceed 3000 h−1.

Considering variation of bearing capacity of foundation caused by crushing of coral sands, the variation of wind resistance reliability of foundation in coral sands was studied. Based on the use of exponential decay model of bearing capacity of foundation, the reliability index of foundation at different time was calculated. Calculation shows that in the mid-term of foundations life in coral sands, attention should be paid to the assessment of wind resistance reliability of foundation, and it is necessary to track the variation of wind resistance performance of foundation in time. After a long time of operation, assessment must be applied to the wind resistance reliability of foundation combining with inspection.

Exampled by Weishan irrigated area, the largest irrigation area in the lower basin of Yellow River, this study summarizes the experience of erosion controlling on desilting highland for years and proposes comprehensive control modes including water diversion irrigation management. After taking the engineering measures such as land leveling, soil mulching and land planishing and the vegetation measures such as slope protection by highland vegetation and shelterbelt network, the desilting highland in Weishan irrigation area was overall controlled, soil erosion and ecological environment deterioration have been restrained effectively.

The internal stress calculation of continuous fiber reinforced composites under transverse loads is a complex problem. This paper established a stress calculation model based on "equal strain method", which greatly simplify the formula derivation. Three internal stress formulas under the transverse loads were derived based on the model. The first is the fiber stress formula, which shows that the ratio of fiber stress to load gradually decreases with increasing of fiber volume fraction. The second is the matrix stress formula, which shows the ratio of matrix stress to load gradually increases with increasing of fiber volume fraction. The third is the formula of average shear stress at the interface of fiber and matrix, which curve shows there is a maximum value of interfacial shear stress. The three formulas have important role for checking intensity.