Oligopeptide Signaling through TbGPR89 Drives Trypanosome Quorum Sensing

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Modeling leaf CO2 assimilation and Photosystem II photochemistry from chlorophyll fluorescence and the photochemical reflectance index

We present a simple model to assess the quantum yield of photochemistry (Φ_P) and CO₂ assimilation rate from two parameters that are detectable by remote sensing: chlorophyll (chl) fluorescence and the photochemical reflectance index (PRI). Φ_P is expressed as a simple function of the chl fluorescence yield (Φ_F) and nonphotochemical quenching (NPQ): Φ_P = 1–bΦ_F(1 + NPQ). Because NPQ is known to be related with PRI, Φ_P can be remotely assessed from solar‐induced fluorescence and the PRI. The CO₂ assimilation rate can be assessed from the estimated Φ_P value with either the maximum carboxylation rate (V_cmax), the intercellular CO₂ concentration (C_i), or parameters of the stomatal conductance model. The model was applied to experimental data obtained for Chenopodium album leaves under various environmental conditions and was able to successfully predict Φ_F values and the CO₂ assimilation rate. The present model will improve the accuracy of assessments of gas exchange rates and primary productivity by remote sensing.     

绿针假单胞菌GP72中aurI/aurR系统调控功能

【背景】绿针假单胞菌(Pseudomonas chlororaphis) GP72是一株可生产吩嗪类抗生素吩嗪-1-羧酸(PCA)和2-羟基吩嗪(2-OH-PHZ)的生防根际促生菌。基因组比对发现GP72菌中存在aurI/aurR双元调控系统。【目的】研究该系统对GP72中吩嗪类物质的调控作用。【方法】将aurI基因在大肠杆菌中异源表达,用紫色杆菌CV026和根癌农杆菌NTL4做显色实验。构建基因敲除菌株和回补菌株,发酵测量突变株的生长曲线与总吩嗪产量。构建转录融合质粒,测定吩嗪合成基因启动子的转录水平。【结果】显色实验显示,aurI能产生多种信号分子,使CV026显紫色、NTL4显蓝色。分别单独敲除aurI和aurR基因,同时敲除aurI/aurR基因,吩嗪产量均会升高,而回补菌株吩嗪产量降为野生型水平。β-半乳糖苷酶活性测定结果显示,突变株的酶活比野生型高。【结论】aurI/aurR负调控GP72的吩嗪合成,通过抑制吩嗪合成启动子的转录而影响吩嗪类物质的产量。     

Validation of magneto-inertial measuring units for measuring hip joint angles

Camera-based motion capture systems are the current gold standard for motion analysis. However, the use of wireless inertial sensor-based systems is increasing in popularity, largely due to convenient portability. The purpose of this study was to validate the use of wireless inertial sensors for measuring hip joint motion with a functional calibration requiring only one motion (walking) and neutral standing. Data were concurrently collected using a 10-camera motion capture system and a wireless inertial sensor-based system. Hip joint angles were measured for 10 participants during walking, jumping jack, and bilateral squat tasks and for a subset (n = 5) a jump turn task. Camera-based system hip joint angles were calculated from retro-reflective marker positions and sensor-based system angles were calculated in MATLAB using the sensor output quaternions. Most hip joint angles measured with the sensor-based system were within 6° of angles measured with the camera motion capture system. Accurate measurement of motion outside of a laboratory setting has broad implications for diagnosing movement abnormalities, monitoring sports performance, and assessing rehabilitation progress.     

Synthesis of d-desthiobiotin-AI-2 as a novel chemical probe for autoinducer-2 quorum sensing receptors

In processes regulated by quorum sensing (QS) bacteria respond to the concentration of autoinducers in the environment to engage in group behaviours. Autoinducer-2 (AI-2) is unique as it can foster interspecies communication. Currently, two AI-2 receptors are known, LuxP and LsrB, but bacteria lacking these receptors can also respond to AI-2. In this work, we present an efficient and reproducible synthesis of a novel chemical probe, d-desthiobiotin-AI-2. This probe binds both LuxP and LsrB receptors from different species of bacteria. Thus, this probe is able to bind receptors that recognise the two known biologically active forms of AI-2, presenting the plasticity essential for the identification of novel unknown AI-2 receptors. Moreover, a protocol to pull down receptors bound to d-desthiobiotin-AI-2 with anti-biotin antibodies has also been established. Altogether, this work highlights the potential of conjugating chemical signals to biotinylated derivatives to identify and tag signal receptors involved in quorum sensing or other chemical signalling processes.     

Using time-lapse digital video recording for a nesting study of birds of prey

Remote photography using various photo, movie or video devices has been employed in numerous studies in wildlife research during the last 50 years. Given the rapid advances in digital technologies, digital video and photo techniques are becoming more common in use, and publications that introduce a new method or equipment for video surveillance in wildlife research (and in ornithological studies particularly) are appearing almost every year. However, still no special guide to the great variety of equipment and methods is available, and the choice and use of suitable gear for scientific purposes may be difficult for non-specialists. In this paper, we review the most common surveillance techniques used in today’s nest studies, as well as the most essential properties of image recording equipment. We also describe the digital video recording technique, which we used for observations of raptor nests, and summarise our experience of its operation. As an example of the obtained data, we present the timing of prey deliveries of goshawks and common buzzards.     

基于GS和GIS的春尺蠖种群分布动态研究

本文利用杀虫灯诱杀春尺蠖雄成虫的数据,采用地统计学空间插值方法,借助遥感（RS）和地理信息系统（GIS）技术,得出2001～2003年和田地区春尺蠖种群空间分布格局及其动态。结果显示,3年中春尺蠖种群均为聚集分布,但聚集程度、种群空间分布和数量处于动态变化之中。通过TM卫片解译提取和田地区森林图层,在ARCGIS中完成对插值模拟图的切割,从而把春尺蠖种群动态的年际分布显示在具体的森林斑块内。研究结果可作为进一步研究春尺蠖种群暴发机理和系统控制的基础。     

Evidence for Megalake Chad, north-central Africa, during the late Quaternary from satellite data

The existence of a very large Lake Chad during the late Quaternary, Megalake Chad, has long been questioned. A Megalake Chad would present strong evidence for climatic fluctuations of great magnitude during the Holocene in tropical Africa. In this paper we used satellite data from Landsat and Modis sensors to collect and analyse new information on landforms in a 2 000 000 km² region of the Lake Chad Basin. We detected 2300 km of remains marking the ancient shoreline of Megalake Chad. The satellite data also indicated many Saharan rivers and relict deltas leading to the long paleoshoreline. Large dunefield flattenings were observed and interpreted as the result of wave-cut erosion by the paleolake. Similarities were noticed between the landforms observed along the paleoshoreline of Megalake Chad and that of the former Aral Sea. This finding has significant consequences for reconstructing paleohydrology and paleoenvironments through the Lake Chad basin, and continental climate change.     

Effect of sediment type on microphytobenthos vertical distribution: Modelling the productive biomass and improving ground truth measurements

Intertidal flats are frequently colonised by microphytobenthos (MPB) assemblages that form transient biofilms at the sediment surface which are responsible for large fractions of estuarine primary production. The large spatio-temporal variability in MPB biomass distribution in concert with the fact that tidal flats can cover many km² makes the use of remote sensing particularly useful in assessing MPB distribution. Water content, sediment type and MPB vertical migration are variables that affect the relationship between ground truth measurements and remote sensing of benthic chlorophyll. The effect of chlorophyll depth distribution (top 2 mm) on the relationship between benthic chlorophyll and several remote sensing indices (NDVI, PI, R562/R647, derivative indices and PAM fluorescence) was investigated over a 2 year sampling period at 6 sites (Tagus estuary, Portugal). Additionally, the effect of the dark adaptation time required to measure the minimum fluorescence parameter (F₀) was also tested. Sediment type strongly affected MPB depth distribution with muddy sites showing a strong negative exponential decay in chlorophyll with distance from the surface while sandy sites had a homogenous distribution over the same scale (2 mm). Chlorophyll content (mass per unit mass, μg g^− 1) in the top 2 mm was better correlated with remote sensing indices than concentration (mass per unit volume, mg m^− 3), both for NDVI (0.72 vs. 0.45) and for PAM fluorescence (0.70 vs. 0.55). Separating the data by transect increased the correlation values in all situations. A fitted model of chlorophyll depth distribution showed that the effect of asymmetrical chlorophyll depth distribution was stronger on the correlations between chlorophyll concentration and NDVI than on chlorophyll content and NDVI (0.46-2 mm vs. 0.74-125 μm, muddy site) the same was valid for fluorescence (0.66-2 mm vs. 0.92-125 μm, muddy site). Dark adapting the samples for more than 5 min did not result in any significant difference in the relationship between F₀ and chlorophyll a. The residuals from the regression of chlorophyll content on NDVI were positively correlated (0.7) with the mass per unit of mass of sediment < 63 μm and negatively (− 0.6) with chlorophyll concentration, this indicates that if no correction is performed to account for chlorophyll depth distribution both units will be strongly affected by the mass of < 63 μm particles. The results demonstrate that although expressing chlorophyll a as concentration is generally a better option for ground truth measurements care should be taken to account for chlorophyll depth distribution since strong asymmetries within the sampling depth can introduce large errors.     

Seasonal changes in chlorophyll distributions in Amazon floodplain lakes derived from MODIS images

To assess seasonal changes in phytoplanktonic chlorophyll distributions in Amazon floodplain lakes, a linear mixing model was applied to Moderate Resolution Imaging Spectroradiometer (MODIS) reflectance data acquired at four river stages: rising (April), high (June), decreasing (September), and low (November). The study area is located in a floodplain reach from Parintins (Amazonas) to near Almeirim (Pará). A three-end-member mixing model designed to uncouple three fractions [high suspended inorganic matter (ip), low inorganic suspended matter (w), and high chlorophyll a (Chl)] was tested in Lake Curuaí (1.5°S 55.43°W) based on field sampling done almost concurrently with satellite overpasses. During high water, phytoplankton patches are confined to lakes closer to terra firme under the influence of clear water inflow, whereas during the low and decreasing water stages, the patches are more evenly distributed over the floodplain.