The bacterial communities of bioelectrochemical systems associated with the sulfate removal under different pHs

Sulfate contamination in ecosystems has been a serious problem. Among various technologies, bioelectrochemical systems (BESs) show the advantage of no-pollution and low-cost for removing sulfate. In order to further expound the biological process of sulfate removal in BESs, 454 pyrosequencing was applied to analyze the bacterial communities under different pH conditions. The bacterial community profiles were analyzed from three aspects: (a) the α-diversity and β-diversity of bacterial communities, (b) the distribution of bacterial phylotypes, and (c) the characterizations of dominant operational taxonomic units (OTUs). We demonstrated that the indexes of phylotype richness and phylogenetic diversity were positively correlated across the pH gradient in the BESs. Among the dominant OTUs, the OTUs which were highly similar to Desulfatirhabdium butyrativorans, Desulfovibrio marrakechensis and Desulfomicrobium sp. might participate in removing sulfate. Standing on genus level, Desulfomicrobium and Sulfuricurvum play conducing and adverse roles for sulfate removal in alkaline condition, respectively. Desulfovibrio contributed to removing sulfate in the neutral and acidic conditions, while Thiomonas mainly weakened the performance of sulfate removal in neutral pH condition. These results further clarified how pH condition directly affected the bacterial communities, which consequently affected the performance of sulfate pollutant treatment using BESs.     

Growth kinetics and mathematical modeling of Synechocystis sp. PCC 6803 under flashing light

In photobioreactors and natural systems, microalgae are subjected to rapidly changing light intensities (LI) due to light attenuation and mixing. A controlled way to study the effect of rapidly changing LI is to subject cultures to flashing light. In this study, series of flashing-light experiments were conducted using Synechocystis sp. PCC6803 with constant overall average LI of approximately 84 μmol·m⁻²·s⁻¹ and relative times in the light and dark varied. The results were also compared with simulated results using a mathematical model including an absorbed pool of light energy, photoacclimation, and photoinhibition. With equal time in light and dark, the specific growth rate (μ) systematically decreased with increasing light duration, and µ decreased further when the ratio of light to dark was decreased. The model captured both trends with the mechanistic explanation that when the light duration was very short the changes in the pool of absorbed LI were smoothed out across the light and dark periods, whereas longer durations caused the biomass to experience discrete light and dark conditions that lead to reduced light absorption, more energy loss to nonphotochemical quenching, and more photodamage. These growth effects were accentuated as the ratio of light to dark decreased.     

钝顶螺旋藻在不同光照条件下的放氧特性

钝顶螺旋藻在持续照光和中等频率 (0.01~20 Hz) 的光/暗交替照光下的放氧特性对光生物反应器的设计和操作具有重要意义。构建了一套可实现光/暗交替的光生物反应器系统对此进行研究,结果显示：根据与放氧速率的关系,可以将光强分为4个区：光限制区 (0~335 μmol/(m2·s)),过渡区 (335~875 μmol/(m2·s)),光饱和区 (875~2 775 μmol/(m2·s)) 以及光抑制区 (2 775 μmol/(m2·s)以上)。提高光/暗频率能否提高微藻光合速率取决于所采用的光强和     

In vivo cytochrome and alternative pathway respiration in leaves of Arabidopsis thaliana plants with altered alternative oxidase under different light conditions

The in vivo activity of the alternative pathway (ν(alt)) has been studied using the oxygen isotope fractionation method in leaves of Arabidopsis thaliana modified for the expression of the AtAOX1a gene by anti-sense (AS-12) or overexpression (XX-2). Under non-stressful conditions, ν(alt) was similar in all plant lines regardless of its different alternative pathway capacities (V(alt)). Total leaf respiration (V(t)) and V(alt) were directly related to growth light conditions while electron partitioning between the cytochrome pathway (CP) and alternative pathway (AP) was unchanged by light levels. Interestingly, the AP functioned at full capacity in anti-sense plants under both growth light conditions. The role of the AP in response to a high light stress induced by short-term high light treatment (HLT) was also studied. In wild type and XX-2, both CP and AP rates increased proportionally after HLT while in AS-12, where the AP was unable to increase its rate, the CP accommodated all the increase in respiration. The results obtained under high light stress suggest that flexibility in the response of the mitochondrial electron transport chain is involved in sustaining photosynthetic rates in response to this stress while the saturated AP in AS-12 plants may contribute to the observed increase in photoinhibition.     

A comparison of primary production measurements using two laboratory systems with differences in light quality

Primary production measurements were carried out simultaneously, using two laboratory systems with different light conditions: (1) a'classical' incubator and (2) a Laboratory Scale Enclosure. The model used for calculating primary production (STEELE, 1965) does not correct for spectral changes caused by high phytoplankton biomass. In the incubator, light of almost all wavelengths decreased more or less according to the attenuation of total PhAR in water. In the LSE, high absorption was found of the blue light and some of the red light, which was due to the high sestonic concentration. The Steele function provided a good fit for both sets of data. The depth integrated gross production values derived from the simultaneous measurements were not significantly different.     

Optimal production of curdlan by Agrobacterium sp. with feedback inferential control of optimal pH profile

The pH control was important for curdlan production with Agrobacterium sp. ATCC31750. Specific cell growth rate was the highest at pH 7 and the specific curdlan production rate was at pH 5.5. The pH profiles maximizing curdlan production was changed from pH 7 optimal for cell growth to pH 5.5 optimal for curdlan production after ammonium consumption. The feedback inferential control methods, with easily measurable variables such as NaOH addition for pH control and dissolved oxygen (DO), were also applied. The pH was successfully controlled to follow optimal profiles and the maximal production of curdlan (60 g l^–1 in 120 h) was achieved with feedback optimal control.     

D‐Root: a system for cultivating plants with the roots in darkness or under different light conditions

In nature roots grow in the dark and away from light (negative phototropism). However, most current research in root biology has been carried out with the root system grown in the presence of light. Here, we have engineered a device, called Dark‐Root (D‐Root), to grow plants in vitro with the aerial part exposed to the normal light/dark photoperiod while the roots are in the dark or exposed to specific wavelengths or light intensities. D‐Root provides an efficient system for cultivating a large number of seedlings and easily characterizing root architecture in the dark. At the morphological level, root illumination shortens root length and promotes early emergence of lateral roots, therefore inducing expansion of the root system. Surprisingly, root illumination also affects shoot development, including flowering time. Our analyses also show that root illumination alters the proper response to hormones or abiotic stress (e.g. salt or osmotic stress) and nutrient starvation, enhancing inhibition of root growth. In conclusion, D‐Root provides a growing system closer to the natural one for assaying Arabidopsis plants, and therefore its use will contribute to a better understanding of the mechanisms involved in root development, hormonal signaling and stress responses.     

不同光照强度下植物电信号变化特征及其与空气负离子的关系

空气负离子(NAI)是衡量一个地区空气清洁度的重要指标,对人体的心理健康和生理机能具有重要的调节作用.植被光合过程中光电效应是NAI产生的重要来源和影响因素,但光电效应极其微弱而难以直接监测,而植物电信号是间接反映光电效应的重要指标,以往研究多侧重在不同森林群落中NAI的时空变化特征及其与气象因素的关系,目前关于NAI...     

Kinetic and growth parameters of Arthrospira (Spirulina) platensis cultivated in tubular photobioreactor under different cell circulation systems

Arthrospira platensis was cultivated in tubular photobioreactor in order to evaluate growth and biomass production at variable photosynthetic photon flux density (PPFD = 60, 120, and 240 μmol photons m(-2)s(-1)) and employing three different systems for cell circulation, specifically an airlift, a motor-driven pumping and a pressurized system. The influence of these two independents variables on the maximum cell concentration (X(m)), cell productivity (P(x)), nitrogen-to-cell conversion factor (Y(X/N) ), photosynthetic efficiency (PE), and biomass composition (total lipids and proteins), taken as responses, was evaluated by analysis of variance. The statistical analysis revealed that the best combination of responses' mean values (X(m) = 4,055 mg L(-1), P(x) = 406 mg L(-1)day(-1), Y(X/N) = 5.07 mg mg(-1), total lipids = 8.94%, total proteins = 30.3%, PE = 2.04%) was obtained at PPFD = 120 μmol photons m(-2)s(-1); therefore, this light intensity should be considered as the most well-suited for A. platensis cultivation in this photobioreactor configuration. The airlift system did not exert any significant positive statistical influence on the responses, which suggests that this traditional cell circulation system could successfully be substituted by the others tested in this work.     

Influence of high frequency light/dark fluctuations on photosynthetic characteristics of microalgae photoacclimated to different light intensities and implications for mass algal cultivation

Oxygen evolution from aScenedesmus obliquus dominated outdoor culture was followed in a small volume chamber, irradiated either by continuous white light or under light/dark frequencies between 0.05 to 5000 Hz, using arrays of high intensity red light emitting diodes (LED's). By placing neutral density filters in the path of the white light, light saturation curves of the oxygen evolution (P/I curves) were measured using diluted aliquots of algal cultures. The results clearly showed that photosynthetic rates increased exponentially with increasing light/dark frequencies, that a longer dark period in relation to the light period does not necessarily lead to higher photosynthetic rates (efficiencies), and that algae do not acclimate to a specific light/dark frequency. One of the most important factors that influenced photosynthetic rates, either under continuous illumination or intermittent, was whether the algae were dark or light acclimated. Low light/dark frequencies were perceived by the algae as low light conditions, whilst the opposite was true for high frequencies. The light utilisation efficiency in a fluctuating light/dark environment depended on the acclimated state of the algae, the specific frequency of the fluctuations and the duration of the exposure. Since the frequencies determined the perceived quantities of light, dark reactions played an important role in determining the average photosynthetic efficiencies. These results have important implications for algal biotechnology.     

A comprehensive time‐course metabolite profiling of the model cyanobacterium Synechocystis sp. PCC 6803 under diurnal light:dark cycles

Cyanobacteria are a model photoautotroph and a chassis for the sustainable production of fuels and chemicals. Knowledge of photoautotrophic metabolism in the natural environment of day/night cycles is lacking, yet has implications for improved yield from plants, algae and cyanobacteria. Here, a thorough approach to characterizing diverse metabolites—including carbohydrates, lipids, amino acids, pigments, cofactors, nucleic acids and polysaccharides—in the model cyanobacterium Synechocystis sp. PCC 6803 (S. 6803) under sinusoidal diurnal light:dark cycles was developed and applied. A custom photobioreactor and multi‐platform mass spectrometry workflow enabled metabolite profiling every 30–120 min across a 24‐h diurnal sinusoidal LD (‘sinLD’) cycle peaking at 1600 μmol photons m^?2 sec^?1. We report widespread oscillations across the sinLD cycle with 90%, 94% and 40% of the identified polar/semi‐polar, non‐polar and polymeric metabolites displaying statistically significant oscillations, respectively. Microbial growth displayed distinct lag, biomass accumulation and cell division phases of growth. During the lag phase, amino acids and nucleic acids accumulated to high levels per cell followed by decreased levels during the biomass accumulation phase, presumably due to protein and DNA synthesis. Insoluble carbohydrates displayed sharp oscillations per cell at the day‐to‐night transition. Potential bottlenecks in central carbon metabolism are highlighted. Together, this report provides a comprehensive view of photosynthetic metabolite behavior with high temporal resolution, offering insight into the impact of growth synchronization to light cycles via circadian rhythms. Incorporation into computational modeling and metabolic engineering efforts promises to improve industrially relevant strain design.     

The responses of a lotic mayfly Nousia sp. (Ephemeroptera: Leptophlebiidae) to moving water and light of different wavelengths

1. Although laboratory studies of the behaviour of aquatic macroinvertebrates are common, there has been little critical evaluation of the importance of test conditions to them. We used a common Australian leptophlebiid mayfly, Nousia sp., to investigate responses to light, wavelength of light, presence or absence of cover and still or flowing water.
2. Nousia sp. showed substantial qualitative differences in behaviour, as measured by movement, when there was no refuge (in the form of a crevice beneath a tile) present in the experimental arena.
3. We found no evidence of diel periodicity in activity in Nousia sp.
4. Nousia sp. did not respond to infra-red, red or green light at a flux density of 18–19 μmol m^–2 s^–1.
5. Nymphs were three times more likely to remain stationary in flowing water (mean velocity 0.10 m s^–1) than in still water.
6. We conclude that generalized assumptions about test conditions for experiments designed to quantify laboratory behaviour in benthic macroinvertebrates are unjustified and that evaluation of the individual requirements of test species should be conducted routinely.     

Carbon nanodots with a controlled N structure by a solvothermal method for generation of reactive oxygen species under visible light

Carbon nanodots can function as photosensitizers that have the ability to generate reactive oxygen species such as singlet oxygen, hydroxy (OH) radicals, and superoxide ions. However, most of these can only be generated upon ultraviolet light excitation. Additionally, the mechanism of reactive oxygen species generation by carbon nanodots remains unclear. The development of carbon nanodots that can photosensitize under visible light irradiation is desirable for applications such as photodynamic therapy and pollutant decomposition under visible light. Here, we report novel carbon nanodot-based photosensitizers that generate reactive oxygen species under visible light; they were synthesized using a solvothermal method with two solvents (formamide and water) and amidol as the carbon source. Carbon nanodots from the solvothermal synthesis in formamide showed blue fluorescence, while those obtained in water showed green fluorescence. The photo-excited blue-fluorescent carbon nanodots produced OH radicals, superoxide ions, and singlet oxygen, and therefore could function as both type I and type II photosensitizers. In addition, photo-excited green-fluorescent carbon nanodots generated only singlet oxygen, therefore functioning as type II photosensitizers. It is proposed that the two photosensitizers have different origins of reactive oxygen species generation: the enrichment of graphitic N for blue-fluorescent carbon nanodots and molecular fluorophores for green-fluorescent carbon nanodots.     

沙漠腹地天然绿洲不同林龄胡杨水分利用来源

了解干旱荒漠绿洲区主要植被的水分利用来源,能为该区域植被保护和水资源的合理分配提供科学依据.本研究以达里雅布依天然绿洲胡杨幼龄木(胸径DBH≤10 cm)、成熟木(10 cm＜DBH≤40 cm)和过熟木(DBH＞40 cm)为对象,测定不同林龄胡杨木质部水和潜在水源(地表水、0～3m土层土壤水、地下水)的氧同位素,运...     

模拟光条件下禾本科植物和藜科植物蒸腾特性与水分利用效率比较

利用人工模拟光源研究了两种 C4 光合途径禾本科植物 (虎尾草、狗尾草 )和两种 C3光合途径藜科植物 (藜、绿藜 )的光合速率 ( Pn)、蒸腾速率 ( Tr)、水分利用率 ( WUE)、气孔导度 ( Gs)、胞间 CO2 浓度 ( Ci)及叶面饱和蒸气压亏缺 ( Vpdl)随模拟光辐射 ( SPR)增强的变化规律及 Gs、Ci、Vpdl对 Tr和 WUE的影响。结果表明 :( 1 ) 4种植物的 Pn和 Tr均随 SPR增强而增大 ,两种藜科植物最大净 Pn和 Tr均高于两种禾本科植物的最大净 Pn和 Tr。 ( 2 ) WUE随 SPR增强先增大后减小 ,两种禾本科植物和两种藜科植物分别在SPR为 40 0、1 2 0 0 μmol/( m2·s)时达到最大值 ,禾本科植物的最大 WUE明显高于藜科植物。 ( 3) 4种植物的 Gs、Ci均随 SPR的增强而减小 ,两种藜科植物的 Gs和 Ci均显著高于两种禾本科植物。4种植物的 Vpdl均随 SPR增强而增大 ,禾本科植物高于藜科植物。实验表明 ,在以水分为限制因素的半干旱草原区 ,禾本科植物具有更好的保水机制和更高的水分利用效率 ,与藜科植物相比 ,在水分生态上具有一定的竞争优势。