Extraction of sterols in brown macroalgae from Antarctica and their identification by liquid chromatography coupled with tandem mass spectrometry

This study reports for the first time the extraction and quantification of sterols in six species of brown macroalgae from Antarctica: Adenocystis utricularis, Ascoseira mirabilis, Cystosphaera jacquinotii, Desmarestia anceps, Desmarestia antarctica, and Himantothallus grandifolius. Ultrasound irradiation was used as a promotor to extract sterols from algal biomass. The extracts were analyzed by high-performance liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) for sterol quantization (ergosterol, brassicasterol, fucosterol, β-sitosterol, campesterol, cholesterol, and stigmasterol). In general, fucosterol was the most abundant (6.60 to 48.13 mg kg^?1), followed by β-sitosterol (5.29 to 16.49 mg kg^?1), stigmasterol (2.69 to 14.84 mg kg^?1) in five of the six examined algae. The sterol campesterol was found in lower concentrations (0.07 to 0.15 mg kg^?1) in all studied samples.     

Functional Analysis of Sinorhizobium meliloti Genes Involved in Biotin Synthesis and Transport

External biotin greatly stimulates bacterial growth and alfalfa root colonization by Sinorhizobium meliloti strain 1021. Several genes involved in responses to plant-derived biotin have been identified in this bacterium, but no genes required for biotin transport are known, and not all loci required for biotin synthesis have been assigned. Searches of the S. meliloti genome database in combination with complementation tests of Escherichia coli biotin auxotrophs indicate that biotin synthesis probably is limited in S. meliloti 1021 by the poor functioning or complete absence of several key genes. Although several open reading frames with significant similarities to genes required for synthesis of biotin in gram-positive and gram-negative bacteria were found, only bioB, bioF, and bioH were demonstrably functional in complementation tests with known E. coli mutants. No sequence or complementation evidence was found for bioA, bioC, bioD, or bioZ. In contrast to other microorganisms, the S. meliloti bioB and bioF genes are not localized in a biotin synthesis operon, but bioB is cotranscribed with two genes coding for ABC transporter-like proteins, designated here bioM and bioN. Mutations in bioM and bioN eliminated growth on alfalfa roots and reduced bacterial capacity to maintain normal intracellular levels of biotin. Taken together, these data suggest that S. meliloti normally grows on exogenous biotin using bioM and bioN to conserve biotin assimilated from external sources.     

Hydrogen uptake by Robinia pseudoacacia nodules

Summary Hydrogen uptake is thought to increase the efficiency of nitrogen fixation by recycling H₂ produced by nitrogenase that would otherwise be lost by diffusion. Here we demonstrate the capacity of eight Rhizobium strains to take up molecular hydrogen. Uptake by nodule homogenates from Robinia pseudoacacia was measured amperometrically under nitrogenase repression. Markedly lower activities were found than in soybean nodules. In addition hydrogenase activity was detected by the ability of bacteroids to reduce methylene blue in the presence of hydrogen. It was demonstrated that hydrogenase structural genes are present in the black locust symbiont, Rhizobium sp. strain R1, using hybridization with a plasmid, which contained hydrogenase genes from R. leguminosarum bv. viceae.     

Transmitter concentration profiles in the synaptic cleft: an analytical model of release and diffusion.

A three-dimensional model for release and diffusion of glutamate in the synaptic cleft was developed and solved analytically. The model consists of a source function describing transmitter release from the vesicle and a diffusion function describing the spread of transmitter in the cleft. Concentration profiles of transmitter at the postsynaptic side were calculated for different transmitter concentrations in a vesicle, release scenarios, and diffusion coefficients. From the concentration profiles the receptor occupancy could be determined using alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor kinetics. It turned out that saturation of receptors and sufficiently fast currents could only be obtained if the diffusion coefficient was one order of magnitude lower than generally assumed, and if the postsynaptic receptors formed clusters with a diameter of roughly 100 nm directly opposite the release sites. Under these circumstances the gradient of the transmitter concentration at the postsynaptic membrane outside the receptor clusters was steep, with minimal cross-talk among neighboring receptor clusters. These findings suggest that for each release site a corresponding receptor aggregate exists, subdividing an individual synapse into independent functional subunits without the need for specific lateral diffusion barriers.     

The Penn State Safety Floor: Part II--Reduction of fall-related peak impact forces on the femur.

The goal of this study was to develop and validate a finite element model (FEM) for use in the design of a flooring system that would provide a stable walking surface during normal locomotion but would also deform elastically under higher loads, such as those resulting from falls. The new flooring system is designed to reduce the peak force on the femoral neck during a lateral fall onto the hip. The new flooring system is passive in nature and exhibits two distinct stiffnesses. During normal activities, the floor remains essentially rigid. Upon impact, the floor collapses and becomes significantly softer. The flooring system consists of a multitude of columns supporting a continuous walking surface. The columns were designed to remain stiff up to a specific load and, after exceeding this load, to deform elastically. The flooring returns to its original shape after impact. Part I of this study presented finite element and experimental results demonstrating that the floor deflection during normal walking remained less than 2 mm. To facilitate the floor's development further, a nonlinear finite element model simulating the transient-impact response of a human hip against various floor configurations was developed. Nonlinearities included in the finite element models were: changing topology of deformable-body-to-deformable-body contact, snap-through buckling, soft tissue stiffness and damping, and large deformations. Experimental models developed for validating the finite element model included an anthropomorphic hip, an impact delivery mechanism, a data collection system, and four hand-fabricated floor tiles. The finite element model discussed in this study is shown to capture experimentally observed trends in peak femoral neck force reduction as a function of flooring design parameters. This study also indicates that a floor can be designed that deflects minimally during walking and reduces the peak force on the femoral neck during a fall-related impact by 15.2 percent.     

Establishment and maintenance of the border of the neural plate in the chick: involvement of FGF and BMP activity.

We have investigated the cell interactions and signalling molecules involved in setting up and maintaining the border between the neural plate and the adjacent non-neural ectoderm in the chick embryo at primitive streak stages. msx-1, a target of BMP signalling, is expressed in this border at a very early stage. It is induced by FGF and by signals from the organizer, Hensen's node. The node also induces a ring of BMP-4, some distance away. By the early neurula stage, the edge of the neural plate is the only major site of BMP-4 and msx-1 expression, and is also the only site that responds to BMP inhibition or overexpression. At this time, the neural plate appears to have a low level of BMP antagonist activity. Using in vivo grafts and in vitro assays, we show that the position of the border is further maintained by interactions between non-neural and neural ectoderm. We conclude that the border develops by integration of signals from the organizer, the developing neural plate, the paraxial mesoderm and the non-neural epiblast, involving FGFs, BMPs and their inhibitors. We suggest that BMPs act in an autocrine way to maintain the border state.     

An approach to multiscale modelling with graph grammars

Background and Aims

Functional–structural plant models (FSPMs) simulate biological processes at different spatial scales. Methods exist for multiscale data representation and modification, but the advantages of using multiple scales in the dynamic aspects of FSPMs remain unclear. Results from multiscale models in various other areas of science that share fundamental modelling issues with FSPMs suggest that potential advantages do exist, and this study therefore aims to introduce an approach to multiscale modelling in FSPMs.

Methods

A three-part graph data structure and grammar is revisited, and presented with a conceptual framework for multiscale modelling. The framework is used for identifying roles, categorizing and describing scale-to-scale interactions, thus allowing alternative approaches to model development as opposed to correlation-based modelling at a single scale. Reverse information flow (from macro- to micro-scale) is catered for in the framework. The methods are implemented within the programming language XL.

Key Results

Three example models are implemented using the proposed multiscale graph model and framework. The first illustrates the fundamental usage of the graph data structure and grammar, the second uses probabilistic modelling for organs at the fine scale in order to derive crown growth, and the third combines multiscale plant topology with ozone trends and metabolic network simulations in order to model juvenile beech stands under exposure to a toxic trace gas.

Conclusions

The graph data structure supports data representation and grammar operations at multiple scales. The results demonstrate that multiscale modelling is a viable method in FSPM and an alternative to correlation-based modelling. Advantages and disadvantages of multiscale modelling are illustrated by comparisons with single-scale implementations, leading to motivations for further research in sensitivity analysis and run-time efficiency for these models.     

Disjunct distribution of the Mediterranean freshwater crab Potamon fluviatile—natural expansion or human introduction?

Human mediated biological invasions are seen as an increasing danger for biodiversity. On the other hand, range expansions are natural processes. It is often practically not possible to tell these processes apart, like in the case of the freshwater crab Potamon fluviatile. This species has a disjunct distribution on the Balkan Peninsula, Italy, Sicily and Malta. An innovative analysis framework involving phylogeographic model selection and temporal coalescent analyses on a mitochondrial dataset (COI and NADH1) could clarify that the origin of the species was on the Balkans and the colonisation of Italy proceeded from the northern Balkans via southern Italy in the Otranto Strait region. The population expansion associated with this invasion was estimated to have taken place 15,000 years before present (95% c.f. 10,000–24,000 years BP). An anthropogenic introduction is therefore implausible and a natural expansion likely. We argue that the species should thus be included in the national conservation management in Italy.