Diversity and assessment of potential risk factors of Gram-negative isolates associated with French cheeses

The goal of this study was to identify at the species level a large collection of Gram-negative dairy bacteria isolated from milks or semi-hard and soft, smear-ripened cheeses (cheese core or surface samples) from different regions of France. The isolates were then assessed for two risk factors, antibiotic resistance and volatile and non-volatile biogenic amine production in vitro. In total, 173 Gram-negative isolates were identified by rrs and/or rpoB gene sequencing. A large biodiversity was observed with nearly half of all Gram-negative isolates belonging to the Enterobacteriaceae family. Overall, 26 different genera represented by 68 species including potential new species were identified among the studied Gram-negative isolates for both surface and milk or cheese core samples. The most frequently isolated genera corresponded to Pseudomonas, Proteus, Psychrobacter, Halomonas and Serratia and represented almost 54% of the dairy collection. After Pseudomonas, Chryseobacterium, Enterobacter and Stenotrophomonas were the most frequently isolated genera found in cheese core and milk samples while Proteus, Psychrobacter, Halomonas and Serratia were the most frequently isolated genera among surface samples. Antibiotic resistance profiles indicated that resistances to the aminosid, imipemen and quinolon were relatively low while more than half of all tested isolates were resistant to antibiotics belonging to the monobactam, cephem, fosfomycin, colistin, phenicol, sulfamid and some from the penam families. Thirty-six% of isolates were negative for in vitro biogenic amine production. Among biogenic amine-producers, cadaverine was the most frequently produced followed by isoamylamine, histamine and putrescine. Only low levels (<75 mg/l) of tyramine were detected in vitro.     

Mechanical simulation of a Proton Exchange Membrane Fuel Cell stack using representative elementary volumes of stamped metallic bipolar plates

The control of the performance of a fuel cell needs the knowledge of mechanical stresses. A finite element model submitted to operational static loads is developed for pure mechanical analysis of a stack. Adapted to practical implementation in the frame of industrial projects, the tool runs on work stations. Modelling and simulations at the early stage of the stack architecture development are mandatory to lower the costs of the stack and to contribute in designing component dimensions and forms, particularly of stamped metallic bipolar plates or clamping systems. The model should also be useful for accurate local analyses and channel geometry of metallic bipolar plates must be modelled in detail. But the number of degrees of freedom is huge and some model simplification is required to compute a whole stack. The homogenisation technique was applied, replacing cell parts with composite finite elements or homogenised representative elementary volumes.     

Milk fat composition modifies the texture and appearance of Cantal-type cheeses but not their flavor

Although the effects of cow diet on cheese sensory properties have been well documented, the putative interactions between the biochemical and microbial milk components and their respective roles in the development of the sensory properties of cheeses have yet to be explored in depth. The aim of this study was to evaluate the specific contribution of milk fat composition to the formation of cheese sensory properties. Two creams with different fat compositions were obtained from cows fed either pasture or maize silage. Cheeses were manufactured from the same skim milk (identical chemical and microbial composition) with either the pasture- or maize silage-origin pasteurized cream added. The gross composition and microbial composition of milks did not vary with cream origin. In milks and cheeses, the fatty acid (FA) profiles were modified by the origin of the cream. The concentrations of C18:0 and unsaturated FA such as cis-9 C18:1, trans-11 C18:1, C18:3n-3, total conjugated linoleic acids, and mono- and polyunsaturated FA were higher in milks and cheeses with the pasture-origin cream than in those with the maize-origin cream. In contrast, the maize milks and cheeses had higher concentrations of short- and medium-chain saturated FA, C16:0, and C18:2n-6. The level of lipolysis was 11% in the cheese rind and only 0.30% in the cheese core. The rind of pasture cheeses had a higher concentration of free C18:0 and C18:3n-3 and a lower concentration of free C14:0 and free C16:0 than the rind of maize cheeses. The levels of major microbial groups were similar in pasture and maize cheeses at different stages of ripening. The pasture cheeses had a more elastic and creamier texture, a yellower color, and a thinner rind than the maize cheeses, but the odor and aroma of cheeses were not affected by the origin of the cream, despite a few modifications in the balance of volatile compounds from FA catabolism. Based on these results, we conclude that milk fat composition modulated by cow diet had a direct role in the texture of the cheese but no effect on flavor. The high degree of lipolysis in cheese rind, along with the higher concentration of long-chain unsaturated free FA in pasture cheeses may be responsible for antimicrobial activity, which could explain differences in the appearance of cheese rind.     

Reg-1α, a New Substrate of Calpain-2 Depending on Its Glycosylation Status

Reg-1α/lithostathine, a protein mainly associated with the digestive system, was previously shown to be overexpressed in the pre-clinical stages of Alzheimer’s disease. In vitro, the glycosylated protein was reported to form fibrils at physiological pH following the proteolytic action of trypsin. However, the nature of the protease able to act in the central nervous system is unknown. In the present study, we showed that Reg-1α can be cleaved in vitro by calpain-2, the calcium activated neutral protease, overexpressed in neurodegenerative diseases. Using chemical crosslinking experiments, we found that the two proteins can interact with each other. Identification of the cleavage site using mass spectrometry, between Gln⁴ and Thr⁵, was found in agreement with the in silico prediction of the calpain cleavage site, in a position different from the one reported for trypsin, i.e., Arg¹¹-Ile¹² peptide bond. We showed that the cleavage was impeded by the presence of the neighboring glycosylation of Thr⁵. Moreover, in vitro studies using electron microscopy showed that calpain-cleaved protein does not form fibrils as observed after trypsin cleavage. Collectively, our results show that calpain-2 cleaves Reg-1α in vitro, and that this action is not associated with fibril formation.     

A theoretical model for the prediction of initial growth angles and sites of fretting fatigue cracks

The crack initiation mechanisms under fretting fatigue conditions are investigated. Fretting fatigue tests have been conducted on an aluminium alloy. Two major crack initiation mechanisms are experimentally observed. They are theoretically identified by employing a simple dislocation dipole model and taking into consideration the reverse sliding along dislocation layers and the influence of the distance between these layers. It is shown that cracks may initiate either by an extrusion-intrusion mechanism or a fatigue tensile process. Two parameters respectively linked to each of these initiation mechanisms are proposed to predict crack location. The theoretical crack initial growth directions and locations are shown to correlate very well with the experimental ones. With regards to these initiation processes, a spall detachment mechanism is proposed considering the interaction of microcracks.     

Gold-nanoparticle-cored Polyferrocenyl Dendrimers: Modes of Synthesis and Functions as Exoreceptors of Biologically Important Anions and Re-usable Redox Sensors

Polyamidoferrocenylalkylthiolate-Au nanoparticles (AuNP) and AuNP-cored polyferrocenyl dendrimers have been assembled either by the ligand-substitution method from dodecanethiolate-AuNP (AB₃ units) or Brust-type direct synthesis from a 1-1 mixture of dodecanethiol and dendronized thiol (AB₉ units). The AuNP-cored polyferrocenyl dendrimers are a new type of dendrimers with a AuNP core. AuNPs containing a nonasilylferrocenyl dendron have been synthesized; they bear respectively 180 and 360 ferrocenyl units at the periphery. These AuNPs selectively recognize the anions H₂PO₄^– and adenosine-5-triphosphate (ATP^2–) with a positive dendritic effect. Recognition is monitored by the appearance of a new wave at a less positive potential in cyclic voltammetry (CV). These AuNP-cored polyferrocenyl dendrimers can form robust modified electrodes that serve as re-usable sensors of ATP^2– by simple washing with CH₂Cl₂.     

Para Miner: a generic pattern mining algorithm for multi-core architectures

In this paper, we present Para Miner which is a generic and parallel algorithm for closed pattern mining. Para Miner is built on the principles of pattern enumeration in strongly accessible set systems. Its efficiency is due to a novel dataset reduction technique (that we call EL-reduction), combined with novel technique for performing dataset reduction in a parallel execution on a multi-core architecture. We illustrate Para Miner’s genericity by using this algorithm to solve three different pattern mining problems: the frequent itemset mining problem, the mining frequent connected relational graphs problem and the mining gradual itemsets problem. In this paper, we prove the soundness and the completeness of Para Miner. Furthermore, our experiments show that despite being a generic algorithm, Para Miner can compete with specialized state of the art algorithms designed for the pattern mining problems mentioned above. Besides, for the particular problem of gradual itemset mining, Para Miner outperforms the state of the art algorithm by two orders of magnitude.     

Effect of Biaxial Strain on Electronic and Thermoelectric Properties of Mg2Si

The electronic and thermoelectric properties of biaxially strained magnesium silicide Mg₂Si are analyzed by means of first-principle calculations and semiclassical Boltzmann theory. Electron and hole doping are examined for different doping concentrations and temperatures. Under strain the degeneracy of the electronic orbitals near the band edges is removed, the orbital bands are warped, and the energy gap closes up. These characteristics are rationalized in the light of the electron density transfers upon strain. The electrical conductivity increases with the biaxial strain, whereas neither the Seebeck coefficient nor the power factor (PF) follow this trend. Detailed analysis of the evolution of these thermoelectric properties is given in terms of the in-plane and cross-plane components. Interestingly, the maximum value of the PF is shifted towards lower temperatures when increasingly intensive strain is applied.