Lower Optimum Temperature Research Articles

Effects of the substituted amino acid residues on the thermal properties of monomeric isocitrate dehydrogenases from a psychrophilic bacterium, Psychromonas marina, and a mesophilic bacterium, Azotobacter vinelandii.

A cold-adapted monomeric isocitrate dehydrogenase from a psychrophilic bacterium, Psychromonas marina (PmIDH), showed a high degree of amino acid sequential identity (64%) to a mesophilic one from a mesophilic bacterium, Azotobacter vinelandii (AvIDH). In this study, eight corresponding amino acid residues were substituted between them by site-directed mutagenesis, and several thermal properties of the mutated IDHs were examined. In the PmIDH mutants, PmL735F, substituted Leu735 of PmIDH by the corresponding Phe of AvIDH, showed higher specific activity and thermostability of activity than wild-type PmIDH, while the H600Y and N741P mutations of PmIDH resulted in decreased specific activity and thermostability of activity. On the other hand, among the AvIDH mutants, AvP718T showed lower optimum temperature and thermostability of activity than wild-type AvIDH. In PmIDH variously combined the H600Y, L735F and N741P mutations, PmH600YL735F, including the H600Y and L735F mutations, showed higher specific activity than PmH600Y and similar optimum temperature and thermostability of activity to PmH600Y. Furthermore, PmL735FN741P exhibited higher specific activity and thermostability of activity than PmN741P. These results indicated that the effects of the three mutations of PmIDH are additive on the specific activity of both PmH600YL735F and PmL735FN741P and on thermostability of PmL735FN741P.

Carbon nanotubes-CuO/SnO2 based gas sensor for detecting H2S in low concentration

Porous CuO/SnO2 nanofibers were prepared by co-dissolution and electrospinning, followed by annealing, and compounded with different amounts of carbon nanotubes (CNTs, 0–5 wt%). The performance of the composite based sensor was tested in different concentrations of H2S range from 0.1 to 0.5 ppm. The results showed that the gas sensor based CuO/SnO2 doped by CNTs (CNTs-CuO/SnO2) has a low optimum operating temperature, 40 °C, good behavior in detecting low concentration H2S, short response and recovery time (8.3 and 11.5 s, respectively). And at the same time, compared with other gases, 3 wt% CNTs-CuO/SnO2 composite nanomaterial had excellent selectivity to H2S at low concentrations. The prepared gas sensor had great advantages in detecting low concentration H2S.

TiO2/InVO4n–n heterojunctions for efficient ammonia gas detection and their sensing mechanisms

In this paper, TiO2/InVO4n–n nanoheterojunctions with enhanced gas sensing performance were successfully synthesized. The TiO2/InVO4-based sensor exhibits relatively low optimum operating temperature of 250 °C, at which the sensitivity and response/recovery time are 30.5 and 10/10 s, respectively, to 100 ppm ammonia gas. The effective detection (Ra/Rg = 1.7) to 1 ppm ammonia signifies the low detection limit of the sensor. Moreover, the sensor possesses evident room temperature response (Ra/Rg = 3.0, 100 ppm) to ammonia gas. Based on these, the enhanced sensing mechanisms of TiO2/InVO4 have been discussed in-depth, which can be ascribed to the synergistic effects of eximious absorption kinetics, outstanding carrier dynamics, unique nanoheterojunction structure and excellent catalytic property. This provides a meaningful guidance for the subsequent nanoheterojunction construction for excellent gas sensor.

Synthesis of Cr2O3 Nanoparticle-Coated SnO2 Nanofibers and C2H2 Sensing Properties

In this work, Cr2O3 nanoparticles and SnO2 nanofibers were fabricated by a sol–gel process and an electrospinning method, respectively. Gas sensitive materials with high sensitivity to C2H2 gas were obtained by coating Cr2O3 nanoparticles on SnO2 nanofibers. The prepared Cr2O3 nanoparticle-coated SnO2 nanofibers (Cr2O3 NPs. coated SnO2 NFs.) were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), X-ray energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and the gas sensing behaviors to C2H2 were studied. The Cr2O3 NPs. coated SnO2 NFs. exhibited low optimal operating temperature, high sensing response, excellent response-recovery time and long-term stability to C2H2. The optimal operating temperature of the measured material to 20 ppm C2H2 was about 220℃ and the C2H2 concentration had a good linear relationship with the response value when the concentration was less than 60 ppm. In addition, a reasonable gas sensing mechanism was proposed which may enhance the gas sensing performances for the Cr2O3 NPs. coated SnO2 NFs. to C2H2.

A High-Performance Pd Nanoparticle (NP)/WO3 Thin-Film-Based Hydrogen Sensor

A new and high-performance Pd nanoparticle (NP)/WO3 thin-film-based sensor is fabricated by vacuum thermal evaporation (VTE) and RF sputtering herein. Based on the remarkable catalytic activity of Pd NPs and high-quality WO3 thin film (20 nm in thickness), excellent hydrogen sensing properties, including a very high sensing response of $\textbf {1.8}\times \textbf {10}^{\textbf {4}}$ (in 1000 ppm H2/air gas at 175°C), an extremely low detecting level (≤5 ppm H2/air), a relatively low optimal operating temperature of 175°C, and a fast sensing speed, are obtained. In addition, the studied Pd NP/WO3-based device shows the advantages of simple structure, low cost, and easy fabrication process. The studied device is, therefore, promising for high-performance hydrogen sensing applications.

Metal-organic framework derived core-shell PrFeO3-functionalized α-Fe2O3 nano-octahedrons as high performance ethyl acetate sensors

Porous core-shell PrFeO3-functionalized α-Fe2O3 nano-octahedrons were synthesized via a facile one-step hydrothermal method using a metal-organic framework as self-sacrificing template. The morphology, crystalline nature, chemical compositions and specific surface area of the as-prepared PrFeO3/α-Fe2O3 nano-octahedrons were comparatively studied by a variety of techniques, including SEM, TEM, XRD, XPS and BET. The experimental results show that the PrFeO3/α-Fe2O3 composite has a novel porous core-shell octahedral structure with a large specific surface area, which indicates that the material possesses more active sites to achieve a sufficient surface chemical reaction. Herein, the gas sensing properties of the α-Fe2O3 with different PrFeO3-functionalized levels were tested, which shows that the PrFeO3/α-Fe2O3 composite realized a high gas response, low optimum operating temperature and superior selectivity to ethyl acetate gas. The response (Rair/Rgas) of the sensor based on PrFeO3/α-Fe2O3 is 22.85 toward 100 ppm ethyl acetate at 206 °C, about 3 times higher than that of pristine α-Fe2O3 sensor. Besides, the sensor possesses a rapid response and recovery speed of 8 s and 9 s for detecting 100 ppm ethyl acetate. The enhanced gas sensing properties of PrFeO3/α-Fe2O3 composite could be attributed to the unique porous core-shell morphology and p-n heterostructure between PrFeO3 and α-Fe2O3.

Evolution and plasticity of thermal performance: an analysis of variation in thermal tolerance and fitness in 22 Drosophila species.

The thermal biology of ectotherms is often used to infer species' responses to changes in temperature. It is often proposed that temperate species are more cold-tolerant, less heat-tolerant, more plastic, have broader thermal performance curves (TPCs) and lower optimal temperatures when compared to tropical species. However, relatively little empirical work has provided support for this using large interspecific studies. In the present study, we measure thermal tolerance limits and thermal performance in 22 species of Drosophila that developed under common conditions. Specifically, we measure thermal tolerance (CTmin and CTmax) as well as the fitness components viability, developmental speed and fecundity at seven temperatures to construct TPCs for each of these species. For 10 of the species, we also measure thermal tolerance and thermal performance following developmental acclimation to three additional temperatures. Using these data, we test several fundamental hypotheses about the evolution and plasticity of heat and cold resistance and thermal performance. We find that cold tolerance (CTmin) varied between the species according to the environmental temperature in the habitat from which they originated. These data support the idea that the evolution of cold tolerance has allowed species to persist in colder environments. However, contrary to expectation, we find that optimal temperature ( Topt) and the breadth of thermal performance ( Tbreadth) are similar in temperate, widespread and tropical species and we also find that the plasticity of TPCs was constrained. We suggest that the temperature range for optimal thermal performance is either fixed or under selection by the more similar temperatures that prevail during growing seasons. As a consequence, we find that Topt and Tbreadth are of limited value for predicting past, present and future distributions of species. This article is part of the theme issue 'Physiological diversity, biodiversity patterns and global climate change: testing key hypotheses involving temperature and oxygen'.

Fabrication of Zinc pyrovanadate (Zn3(OH)2V2O7·2H2O) nanosheet spheres as an ethanol gas sensor

It is necessary to conveniently and quickly detect the concentrations of ethanol in different environments. A new type of zinc pyrovanadate (Zn3(OH)2V2O7·2H2O) nanosheet spheres is obtained by a convenient single cation-exchange process using sodium vanadate (Na5V12O32) nanowires as precursor, without introducing any surfactant as a catalyst or structure-directing agent. During the exchange of Zn2+ and Na + ions, the Na5V12O32 nanowires gradually transfer to Zn3(OH)2V2O7·2H2O nanosheet spheres along with dissolution of the precursor and precipitation of new nanosheets. The synthetic mechanism of Zn3(OH)2V2O7·2H2O nanosheet spheres is studied by examining the changes of morphological properties of intermediate products at different times. Gas sensors based on these Zn3(OH)2V2O7·2H2O nanosheet spheres are tested. The sensor displays a response value of 1.68–100 ppm concentration of ethanol gas, and reveals a relatively high sensitivity at a relatively low optimal operating temperature of 300 °C, as well as relatively good stability.

Crystal structure of the cold-adapted haloalkane dehalogenase DpcA from Psychrobacter cryohalolentis K5.

Haloalkane dehalogenases (HLDs) convert halogenated aliphatic pollutants to less toxic compounds by a hydrolytic mechanism. Owing to their broad substrate specificity and high enantioselectivity, haloalkane dehalogenases can function as biosensors to detect toxic compounds in the environment or can be used for the production of optically pure compounds. Here, the structural analysis of the haloalkane dehalogenase DpcA isolated from the psychrophilic bacterium Psychrobacter cryohalolentis K5 is presented at the atomic resolution of 1.05 Å. This enzyme exhibits a low temperature optimum, making it attractive for environmental applications such as biosensing at the subsurface environment, where the temperature typically does not exceed 25°C. The structure revealed that DpcA possesses the shortest access tunnel and one of the most widely open main tunnels among structural homologs of the HLD-I subfamily. Comparative analysis revealed major differences in the region of the α4 helix of the cap domain, which is one of the key determinants of the anatomy of the tunnels. The crystal structure of DpcA will contribute to better understanding of the structure-function relationships of cold-adapted enzymes.

In Silico insights on enhancing thermostability and activity of a plant Fructosyltransferase from Pachysandra terminalis via introduction of disulfide bridges

Drawbacks of industrially-used fructosyltransferases (FTs) such as low optimum temperature and low fructooligosaccharides (FOS) yield necessitates the search for engineered FTs that are highly thermostable and active. With the availability of the first plant FT crystal structure from Pachysandra terminalis (PDB ID: 3UGH), computer-aided protein engineering of plant FT is now feasible. To obtain insights on the effect of specific mutations i.e. disulfide bridge introduction, wild-type and mutant FTs were subjected to a 15 μs Martini Coarse-grained Molecular Dynamics (CGMD) simulations at 303 K and 334 K. We report here the five mutants, M31C-Q49C, L144C-S193C, P34C-W300C, S219C-L226C and V470C-S498C with enhanced thermostabilities and/or activities relative to the wild type. Interestingly, M31C-Q49C, which is located within the catalytic-carrying blade of the catalytic domain, has an activity enhancement at both temperatures. At 334 K, three mutations, L144C-S193C, P34C-W300C and V470C-S498C, achieved thermostability relative to the wild type. Intriguingly, both activity and stability enhancement exhibited only at 334 K can be achieved provided that the mutation is located either on the catalytic-carrying residue blade of the catalytic domain or on the non-catalytic domain. Our results suggest that V470C-S498C and L144C-S193C are promising mutants and that domain-specific approach may be exploited to customize enzyme properties.

The Role of Low Soil Temperature for Photosynthesis and Stomatal Conductance of Three Graminoids From Different Elevations.

In high-elevation grasslands, plants can encounter periods with high air temperature while the soil remains cold, which may lead to a temporary mismatch in the physiological activity of leaves and roots. In a climate chamber experiment with graminoid species from three elevations (4400, 2400, and 250 m a.s.l.), we tested the hypothesis that soil temperature can influence photosynthesis and stomatal conductance independently of air temperature. Soil monoliths with swards of Kobresia pygmaea (high alpine), Nardus stricta (lower alpine), and Deschampsia flexuosa (upper lowland) were exposed to soil temperatures of 25, 15, 5, and -2°C and air temperatures of 20 and 10°C for examining the effect of independent soil and air temperature variation on photosynthesis, leaf dark respiration, and stomatal conductance and transpiration. Soil frost (-2°C) had a strong negative effect on gas exchange and stomatal conductance in all three species, independent of the elevation of origin. Leaf dark respiration was stimulated by soil frost in D. flexuosa, but not in K. pygmaea, which also had a lower temperature optimum of photosynthesis. Soil cooling from 15 to 5°C did not significantly reduce stomatal conductance and gas exchange in any of the species. We conclude that all three graminoids are able to maintain a relatively high root water uptake in cold, non-frozen soil, but the high-alpine K. pygmaea seems to be especially well adapted to warm shoot – cold root episodes, as it has a higher photosynthetic activity at 10 than 20°C air temperature and does not up-regulate leaf dark respiration upon soil freezing, as was observed in the grasses from warmer climates.

Enhanced Methane Sensing Properties of WO₃ Nanosheets with Dominant Exposed (200) Facet via Loading of SnO₂ Nanoparticles.

Methane detection is extremely difficult, especially at low temperatures, due to its high chemical stability. Here, WO3 nanosheets loaded with SnO2 nanoparticles with a particle size of about 2 nm were prepared by simple impregnation and subsequent calcination using SnO2 and WO3·H2O as precursors. The response of SnO2-loaded WO3 nanosheet composites to methane is about 1.4 times higher than that of pure WO3 at the low optimum operating temperature (90 °C). Satisfying repeatability and long-term stability are ensured. The dominant exposed (200) crystal plane of WO3 nanosheets has a good balance between easy oxygen chemisorption and high reactivity at the dangling bonds of W atoms, beneficial for gas-sensing properties. Moreover, the formation of a n–n type heterojunction at the SnO2-WO3 interface and additionally the increase of specific surface area and defect density via SnO2 loading enhance the response further. Therefore, the SnO2-WO3 composite is promising for the development of sensor devices to methane.

Innovative approach in Legionella water treatment with photodynamic cationic amphiphilic porphyrin

Abstract Legionella is an opportunistic premise plumbing pathogen that can be present in municipal and other water supplies. Building water systems may provide conditions (such as low flow, water hardness, low disinfectant residual levels and optimal temperature) that accelerate Legionella growth to levels that may result in an increased risk to public health. The standard disinfection of water systems (periodic overheating of water and chlorination) in the interest of prevention of Legionnaires' disease have often proved to be inefficient. It is therefore necessary to develop new approaches for removing Legionella from water systems. One of the new methods is antimicrobial photodynamic therapy (aPDT), which includes the combined activity of a photosensitizer (PS), molecular oxygen and visible light of appropriate wavelength to create singlet oxygen (1O2) and other oxygen reactive species (ROS) leading to the oxidation of numerous cellular components and cell death. In this study, a newly synthesized cationic, amphiphilic porphyrin TMPyP3-C17H35, was tested against Legionella in tap water. The minimal effective concentration (MEC) of PS photoinactivation test and PS uptake assay in sterile tap water were explored to determine the anti-Legionella activity. The complete inactivation of Legionella in sterile tap water was achieved with 0.024 μM of the PS. Also, the tested PS was found to be very effective in reducing Legionella growth in the sterile tap water and photoinactivation was dose-dependent. The tested PS binds well to the bacterial cell, after only 10 minutes of incubation in the dark. In conclusion, these studies indicate that TMPyP3-C17H35 is highly efficient in aPDT which leads to reducing Legionella growth in sterile tap water, and these results suggest that cationic amphiphilic photosensitizers may have a broader application in the photoinactivation of bacterial cells implicated in water disinfection.

Microwave-assisted preparation of hierarchical CuO@rGO nanostructures and their enhanced low-temperature H2S-sensing performance

Hierarchical CuO@rGO nanostructures, consisting of CuO nanoparticles (NPs) and reduced graphene oxide (rGO) nanosheets, were prepared with a normal-pressure microwave-assisted in-situ growth process. In the CuO@rGO composites, CuO NPs with a size range of 4–11 nm are uniformly anchored on rGO surfaces. In contrast, CuO particles of large and non-uniform distribution in the CuO-doped rGO nanosheets (CuO/rGO) were prepared by a conventional hydrothermal method. The CuO@rGO sensors show high response and selectivity to H2S (1–10 ppm) at low operating temperatures (50–150 °C). The mass ratio of copper acetate to graphene oxide during preparation (6–10) is found to highly influence the gas-sensing properties, and the 8-CuO@rGO sample shows the highest H2S-sensing performance at 100 °C. Compared with pristine CuO nanocrystals, the 8-CuO@rGO composite exhibits considerably enhanced gas-sensing performance, such as good response, high selectivity and low optimal temperature. The improved H2S-sensing performance of the CuO@rGO composites can be attributed to the synergistic effect in components and their hierarchical nanostructure.

Ammonia Sensing Characteristics of a Tungsten Trioxide Thin-Film-Based Sensor

A tungsten trioxide (WO3) thin-film-based ammonia sensor device prepared using radio frequency sputtering is reported and studied. A very thin WO3 film (~10 nm) is employed in the studied device. Experimentally, the studied device exhibits a high ammonia sensing response of 13.7 (at 1000-ppm NH3/air, 250 °C), an extremely low detection level (≤10-ppb NH3/air, 250 °C), a relatively low optimal operating temperature of 250 °C, and a widespread sensing concentration range. Furthermore, the device shows advantages including a simple structure, easy fabrication, and relatively lower operating temperature (≤250 °C). Thus, the proposed WO3 thin-film-based sensor device is promising for high-performance ammonia sensing applications.

Preparation of highly crystalline NiO meshed nanowalls via ammonia volatilization liquid deposition for H2S detection

Novel NiO meshed nanowalls, with characteristics of open geometry, porosity, single crystal and highly crystalline framework, are grown in situ on different substrates (including Al2O3 tube, glass slide, ITO, stainless steel mesh, nickel foam and carbon cloth) via a simple ammonia volatilization liquid deposition process at room temperature and a postcalcination treatment. The calcination temperature can strongly influence the pore size and crystallinity of the product, leading to different gas-sensing performances. The product that obtained at 700 °C (NiO-700) has the advantage in the combination of the largest pore size and high crystallinity, and shows the highest response to H2S gas. In 0.01–100 ppm H2S gas, the NiO-700 meshed nanowalls based sensor can give evident and reversible response signals at a low optimal operating temperature of 50 °C, the response towards 100 ppm H2S can reach to 137.3, the detection limit is as low as 10 ppb. Furthermore, the sensor also exhibits excellent selectivity, repeatability, anti-humidity and long-term stability for H2S detection. The results of gas chromatograph-mass spectrometry (GC-MS) and infrared gas analysis (IRGA) reveal that the H2S gas can be oxidized to SO2 after interacting with NiO-700 meshed nanowalls material. Therefore, the possible H2S sensing mechanism should be proposed as: H2S gas molecules undergo a redox reaction with adsorbed oxygen anion on the surface of NiO-700 meshed nanowalls to form SO2; meanwhile, the electrons restricted by adsorbed oxygen return to the bulk and recombine with the holes, resulting in a decrease in effective carrier concentration of holes and thus generating a change in resistance.

Heterologous expression and biochemical characterization of a novel cold-active α-amylase from the Antarctic bacteria Pseudoalteromonas sp. 2-3

α-Amylase is an endo-acting enzyme which catalyzes random hydrolysis of starch. These enzymes are used in various biotechnological processes including the textile, paper, food, biofuels, detergents and pharmaceutical industries. The use of active enzymes at low temperatures has a high potential because these enzymes would avoid the demand for heating during the process thereby reducing costs. In this work, the gene of α-amylase from Pseudoalteromonas sp. 2–3 (Antarctic bacteria) has been sequenced and expressed in Escherichia coli BL21(DE3). The ORF of the α-amylase gene cloned into pET22b(+) is 1824 bp long and codes for a protein of 607 amino acid residues including a His6-tag. The mature protein has a calculated molecular mass of 68.8 kDa. Recombinant α-amylase was purified with Ni-NTA affinity chromatography. The purified enzyme is active on potato starch with a Km of 6.94 mg/ml and Vmax of 0.27 mg/ml*min. The pH optimum is 8.0 and the optimal temperature is 20 °C. This enzyme was strongly activated by Ca2+; results consistent with other α-amylases. To the best of our knowledge, this enzyme has the lowest temperature optimum so far reported for α-amylases.

Precipitated cobalt doped ZnO nanoparticles with enhanced low temperature xylene sensing properties

Metal oxide nanoparticles are fabricated by co-precipitation method. The structural, morphological, optical and room temperature magnetic studies are discussed and outlined the end results along with sensing properties of ZnO and Co doped ZnO nanoparticles. Further, insights of theoretical and experimental aspects analogous with such systems are also discussed. Photoluminescence property indicates that cobalt doping improves the formation of Oxygen species which results in the enhancement of the magnetism and sensor response. The sensitive and selective detection of p-Xylene, particularly distinguishing between Ethanol and Acetone can be attributed to the tuned catalytic activity of Cobalt components, which induce preferential dissociation of p-Xylene into more active species, as well as the substantial increase of resistance with the variation in the nearby chemical environment because of large formation of Schottky barriers. This confirms that Co doped ZnO nanoparticles found to be a good candidate for detecting p-Xylene gas at low concentrations as well as at low optimum temperature.

Diatom Biogeography From the Labrador Sea Revealed Through a Trait-Based Approach

Diatoms are a keystone algal group, with diverse cell morphology and a global distribution. The biogeography of morphological, functional and life-history traits of marine diatoms were investigated in Arctic and Atlantic waters of the Labrador Sea during the spring bloom (2013-2014). In this study, trait-based analysis using community-weighted means showed that low temperatures (<0oC) in Arctic waters correlated positively with diatom species that have traits such as low temperature optimum growth and the ability to produced ice-binding proteins, highlighting their sea-ice origin. High silicate concentrations in Arctic waters, as well as sea-ice cover and shallow bathymetry, favoured diatom species that were heavily silicified, colonial and capable of producing resting spores, suggesting that these are important traits for this community. In Atlantic waters, diatom species with large surface area to volume ratios were dominant in deep mixed layers, whilst low silicate to nitrate ratios correlated positively with weakly silicified species. Sharp cell projections, such as processes or spines, were positively correlated with water-column stratification, indicating that these traits promote positive buoyancy for diatom cells. Our trait-based analysis directly links cell morphology and physiology with diatom species distribution, highlighting allowing new insights on how this method can potentially be applied to explain ecophysiology and shifting biogeographical distributions in a warming climate.

Contrasting distribution patterns between aquatic and terrestrial Phytophthora species along a climatic gradient are linked to functional traits

Diversity of microbial organisms is linked to global climatic gradients. The genus Phytophthora includes both aquatic and terrestrial plant pathogenic species that display a large variation of functional traits. The extent to which the physical environment (water or soil) modulates the interaction of microorganisms with climate is unknown. Here, we explored the main environmental drivers of diversity and functional trait composition of Phytophthora communities. Communities were obtained by a novel metabarcoding setup based on PacBio sequencing of river filtrates in 96 river sites along a geographical gradient. Species were classified as terrestrial or aquatic based on their phylogenetic clade. Overall, terrestrial and aquatic species showed contrasting patterns of diversity. For terrestrial species, precipitation was a stronger driver than temperature, and diversity and functional diversity decreased with decreasing temperature and precipitation. In cold and dry areas, the dominant species formed resistant structures and had a low optimum temperature. By contrast, for aquatic species, temperature and water chemistry were the strongest drivers, and diversity increased with decreasing temperature and precipitation. Within the same area, environmental filtering affected terrestrial species more strongly than aquatic species (20% versus 3% of the studied communities, respectively). Our results highlight the importance of functional traits and the physical environment in which microorganisms develop their life cycle when predicting their distribution under changing climatic conditions. Temperature and rainfall may be buffered differently by water and soil, and thus pose contrasting constrains to microbial assemblies.