Multiscale optical flow computation from the monogenic signal

We have developed an algorithm for the estimation of cardiac motion from medical images. The algorithm exploits monogenic signal theory, recently introduced as an N-dimensional generalization of the analytic signal. The displacement is computed locally by assuming the conservation of the monogenic phase over time. A local affine displacement model replaces the standard translation model to account for more complex motions as contraction/expansion and shear. A coarse-to-fine B-spline scheme allows a robust and effective computation of the models parameters and a pyramidal refinement scheme helps handle large motions. Robustness against noise is increased by replacing the standard pointwise computation of the monogenic orientation with a more robust least-squares orientation estimate. This paper reviews the results obtained on simulated cardiac images from different modalities, namely 2D and 3D cardiac ultrasound and tagged magnetic resonance. We also show how the proposed algorithm represents a valuable alternative to state-of-the-art algorithms in the respective fields.     

Hydrogen production by the hyperthermophilic bacterium <Emphasis Type="Italic">Thermotoga maritima</Emphasis> part I: effects of sulfured nutriments,with thiosulfate as model,on hydrogen production and growth

Background

Thermotoga maritima and T. neapolitana are hyperthermophile bacteria chosen by many research teams to produce bio-hydrogen because of their potential to ferment a wide variety of sugars with the highest theoretical H₂/glucose yields. However, to develop economically sustainable bio-processes, the culture medium formulation remained to be optimized. The main aim of this study was to quantify accurately and specifically the effect of thiosulfate, used as sulfured nutriment model, on T. maritima growth, yields and productivities of hydrogen. The results were obtained from batch cultures, performed into a bioreactor, carefully controlled, and specifically designed to prevent the back-inhibition by hydrogen.

Results

Among sulfured nutriments tested, thiosulfate, cysteine, and sulfide were found to be the most efficient to stimulate T. maritima growth and hydrogen production. In particular, under our experimental conditions (glucose 60 mmol L^?1 and yeast extract 1 g L^?1), the cellular growth was limited by thiosulfate concentrations lower than 0.06 mmol L^?1. Under these conditions, the cellular yield on thiosulfate (Y X/Thio) could be determined at 3617 mg mmol^?1. In addition, it has been shown that the limitations of T. maritima growth by thiosulfate lead to metabolic stress marked by a significant metabolic shift of glucose towards the production of extracellular polysaccharides (EPS). Finally, it has been estimated that the presence of thiosulfate in the T. maritima culture medium significantly increased the cellular and hydrogen productivities by a factor 6 without detectable sulfide production.

Conclusions

The stimulant effects of thiosulfate at very low concentrations on T. maritima growth have forced us to reconsider its role in this species and more probably also in all thiosulfato-reducer hyperthermophiles. Henceforth, thiosulfate should be considered in T. maritima as (1) an essential sulfur source for cellular materials when it is present at low concentrations (about 0.3 mmol g^?1 of cells), and (2) as both sulfur source and detoxifying agent for H₂ when thiosulfate is present at higher concentrations and, when, simultaneously, the pH₂ is high. Finally, to improve the hydrogen production in bio-processes using Thermotoga species, it should be recommended to incorporate thiosulfate in the culture medium.

     

Tyrosol degradation via the homogentisic acid pathway in a newly isolated Halomonas strain from olive processing effluents

Aims: To isolate a new Halomonas sp. strain capable of degrading tyrosol, a toxic compound present in olive mill wastewater, through the homogentisic acid (HGA) pathway. Methods and Results: A moderately halophilic Gram‐negative bacterium belonging to the Halomonas genus and designated strain TYRC17 was isolated from olive processing effluents. This strain was able to completely degrade tyrosol (2‐(p‐hydroxyphenyl)‐ethanol), a toxic compound found in such effluent. Tyrosol degradation begins by an oxidation to 4‐hydroxyphenylacetic acid (HPA), which is then converted into HGA by an HPA 1‐monooxygenase, while closest Halomonas species degrade tyrosol through 3,4‐dihydroxyphenylacetic acid (DHPA). In the presence of transition metals, HGA underwent a pH‐dependent abiotic conversion into benzoquinone acetic acid, then into 2,5‐dihydroxybenzaldehyde (gentisaldehyde) and pyomelanin, by oxidative decarboxylation and polymerization, respectively. Conclusions: Tyrosol degradation via HGA by the new Halomonas sp. strain TYRC17 was complete in the absence of trace elements. In their presence, HGA was abiotically converted into gentisaldehyde and pyomelanin. Significance and Impact of the Study: This is the first report on tyrosol degradation via the HGA pathway under hypersaline conditions and on the oxidative decarboxylation of HGA into gentisaldehyde. It underlines the importance of the Halomonas genus in the bioremediation of toxic‐contaminated sites.     

Bioconversion of tyrosol into hydroxytyrosol and 3,4-dihydroxyphenylacetic acid under hypersaline conditions by the new Halomonas sp. strain HTB24

This paper reports the characterization of a Halomonas sp. strain (named HTB24) isolated from olive-mill wastewater and capable of transforming tyrosol into hydroxytyrosol (HT) and 3,4-dihydroxyphenylacetic acid (DHPA) in hypersaline conditions. This is the first time that a halophile has been shown to perform such reactions. The potent natural antioxidant HT was obtained through a C3 hydroxylation on the ring cycle, whereas DHPA was synthesized via the 4-hydroxyphenylacetic acid (HPA) pathway, which has been well described from other bacterial sources. HT was produced first, and then DHPA was detected in the medium accompanied by traces of HPA. HPA involved another pathway resulting from the activity of an aryl-dehydrogenase, which is suggested to be responsible for both tyrosol and hydroxytyrosol oxidation. Maximal HT content (2.30 mM) and maximal DHPA (5.15+/-0.42 mM) were obtained from a culture inoculated in the presence of 20 mM tyrosol and 0.5 g L(-1) yeast extract. Following this, DHPA was quickly degraded into 5-carboxymethyl-2-hydroxymuconic semialdehyde by a 2,3-dioxygenase, finally resulting in succinate and pyruvate. Phylogenetic analysis of the 16S rRNA gene revealed that this isolate was a member of the genus Halomonas. Strain HTB24, with a G+C content of 55.3 mol%, is closely related to Halomonas neptunia DSM 15720(T), 'Halomonas alkaliantarctica' DSM 15686(T) and Halomonas boliviensis DSM 15516(T).     

Computational model of the movement of the human muscles of mastication during opening and closing of the jaw

Muscle fibre bundles comprising the four major muscles of mastication in the human being were studied in cadavers. Markers were placed along each muscle fibre bundle by means of serial dissections. The 3D coordinates of each marker were tabulated and imported to Cinema 4D, a software animation program. Origins and insertions of each fibre bundle were also digitized and imported, as were the coordinates of the surface of the skull, the mandible and temporomandibular joint. It was then possible to visualize the movement of all relevant fibre bundles during the passive motions of the mandible. An animated film depicts the positions of all relevant muscle fibres during passive movement of the mandible. The properties of the masseter muscle were documented as a prototype for the eventual study of all the muscles of mastication. One can now proceed to study the inverse problem, namely the forces within each fibre bundle that actively generate mandibular motion. It is hoped that these studies will aid in the management of conditions affecting the temporomandibular joint.     

Hydrogen production by the hyperthermophilic bacterium <Emphasis Type="Italic">Thermotoga maritima</Emphasis> Part II: modeling and experimental approaches for hydrogen production

Background

Thermotoga maritima is a hyperthermophilic bacterium known to produce hydrogen from a large variety of substrates. The aim of the present study is to propose a mathematical model incorporating kinetics of growth, consumption of substrates, product formations, and inhibition by hydrogen in order to predict hydrogen production depending on defined culture conditions.

Results

Our mathematical model, incorporating data concerning growth, substrates, and products, was developed to predict hydrogen production from batch fermentations of the hyperthermophilic bacterium, T. maritima. It includes the inhibition by hydrogen and the liquid-to-gas mass transfer of H₂, CO₂, and H₂S. Most kinetic parameters of the model were obtained from batch experiments without any fitting. The mathematical model is adequate for glucose, yeast extract, and thiosulfate concentrations ranging from 2.5 to 20 mmol/L, 0.2–0.5 g/L, or 0.01–0.06 mmol/L, respectively, corresponding to one of these compounds being the growth-limiting factor of T. maritima. When glucose, yeast extract, and thiosulfate concentrations are all higher than these ranges, the model overestimates all the variables. In the window of the model validity, predictions of the model show that the combination of both variables (increase in limiting factor concentration and in inlet gas stream) leads up to a twofold increase of the maximum H₂-specific productivity with the lowest inhibition.

Conclusions

A mathematical model predicting H₂ production in T. maritima was successfully designed and confirmed in this study. However, it shows the limit of validity of such mathematical models. Their limit of applicability must take into account the range of validity in which the parameters were established.

     

Identification of different alkane hydroxylase systems in Rhodococcus ruber strain SP2B,an hexane‐degrading actinomycete

Aims: To investigate the alkane‐hydroxylating system of isolate SP2B, closely related to Rhodococcus ruber DSM 43338^T and uncharacterized so far for its alkane degradation genes. Methods and Results: Although isolate SP2B and reference strain can grow on by‐products from hexane degradation, the type strain R. ruber was unable, unlike SP2B isolate, to use short‐chain alkanes, as assessed by gas chromatography. Using PCR with specific or degenerated primers, inverse PCR and Southern blot, two alkane hydroxylase encoding genes (alkB) were detected in both bacteria, which is in agreement with their alkane range. The first AlkB was related to Rhodococcus AlkB7 enzymes and contains a nonbulky residue at a specific position, suggesting it might be involved in medium‐ and long‐chain alkane oxidation. The second partial alkB gene potentially belongs to alkB5‐type, which was found in bacteria unable to use hexane. Moreover, a partial P450 cytochrome alkane hydroxylase, thought to be responsible for the hexane degradation, was detected only in the isolated strain. Conclusions: Rhodococcus ruber SP2B should prove to be a promising candidate for bioremediation studies of contaminated sites because of its large degradation range of alkanes. Significance and Impact of the Study: This is the first thorough study on R.ruber alkane degradation systems.     

Rhizosphere bacterial populations of metallophyte plants in heavy metal-contaminated soils from mining areas in semiarid climate

Rhizosphere bacterial populations associated with four metallophyte plants in one of major polymetallic (Pb–Zn–Cu) semiarid Moroccan Hercynian province (Draâ Sfar, Marrakech, Morocco) presenting long-term contamination mainly with Zn and Pb were analysed and compared to selected control soils. In the highly Zn-, Cu-, Pb- and Cd- contaminated soils, the total number of culturable heterotrophic bacteria were found in low proportions (< 2.6 × 10² – 1.6 × 10⁴ g^–1soil). This bacterial content was slightly similar to that found in moderately polluted and controls soils (6.7 × 10⁴ – 5.8 × 10⁶). However, the bacterial diversity and the rhizosphere/soil ratio, which compares the bacterial content (or bacterial charge) around the metallophyte plants with that in non-rhizosphere soil, were the bacteriological parameters mostly affected by heavy metal contamination. The chronic Zinc-stress results in an increase of tolerance to this metal of both the rhizosphere and non-rhizosphere bacterial communities. However, in general, the rhizosphere bacterial populations exhibited less tolerance to Zn toxicity than the bacterial population of non-rhizosphere soils. This result suggests that toxic effects of Zn decrease in the rhizosphere soils of the metallophyte plants.