The structural and the photoelectrochemical properties of ZnO–ZnS/ITO 1D hetero-junctions prepared by tandem electrodeposition and surface sulfidation: on the material processing limits

ZnO nanorods were electrodeposited on ITO and immersed in a Na₂S solution for a variable time. As a function of this experimental parameter, different ZnS surface growth mechanisms take place, leading to specific microstructures.

Photoelectrochemical properties of nanocrystalline ZnS discrete versus continuous coating of ZnO nanorods prepared by electrodeposition

The photoelectrochemical properties of nanocrystalline ZnS discrete versus continuous coating of ZnO nanorods prepared by electrodeposition were investigated.

Isolation and characterization of plant growth promoting traits of a rhizobacteria: Pantoea agglomerans lma2

The use of microbial technology in agriculture is expanding quickly with the identification of new bacterial strains which are more effective in promoting the growth of plants. The rhizobacteria that promote the growth of plants can have a positive effect on the productivity of crops especially when subjected to salt stress. A nitrogen-fixing bacterium was isolated from the wheat rhizosphere of an arid region. The strain was identified on the basis of tests API20E and 16S rRNA sequencing, as Pantoea agglomerans lma2. This strain degraded several carbon sources: sugars (fructose, ribose, dextrin, salicin...), lipids (lecithin, tributyrin and tween 80), proteins (gelatin, casein), grew on KCN and could grow from pH 4 to 8 and had an optimum at pH 7. The growth temperature showed a maximum at 30 degrees C and the bacteria could tolerate from 4 to 41 degrees C and the growth rate was higher when the NaCl concentration was between 100 and 300 mM. The performance of activities enhancing the growth of plants of P. agglomerans lma2 was significantly better in the presence of salt. Rates of Indole Acetic Acid (IAA), siderophores production and solubilization of phosphate increased between 100 and 400 mM NaCl compared to the control without salt. The maximum values were saved to 300 mM for the production of siderophores (18.32%) and solubilization of phosphate (1061.49 microg mL(-1)) and 100 mM for the production of IAA (161 microg mL(-1)). A significant correlation existed between these three activities. These results showed that P. agglomerans lma2 with its Plant Growth Promoting Rhizobacteria (PGPR) and halophilic properties could constitute a good fertilizer in arid and saline zone.

Cytotoxic, genotoxic and antigenotoxic potencies of oligorutins

Rutin has been enzymatically oligomerized by laccase from Trametes versicolor. Five fractions of oligomers were obtained from the monomers having high solubility in water, which can reach 351-times that of rutin. Cytotoxicity of rutin and oligorutin fractions was evaluated towards K562 cells. Oligorutin fractions showed a lower antiproliferative effect compared with its monomer. The genotoxic potential of rutin and oligorutin fractions was assessed, at the limit of the solubility of each molecule, using the comet test. None of the tested concentrations of either rutin or oligorutin fractions has showed a genotoxic effect. Similarly, the antigenotoxic effect of these flavonoids was tested using the same assay. The obtained results showed a higher ability of oligorutin fractions to reduce the genotoxicity induced by hydrogen peroxide compared with monomeric rutin.

Effect of Azotobacter vinelandii and compatible solutes on germination wheat seeds and root concentrations of sodium and potassium under salt stress

The effect of plant growth-promoting Rhizobacteria (PGPR) and exogenous application of compatible solutes on seed germination and root concentrations of sodium and potassium of two wheat varieties (Triticum durum L.) were evaluated under saline stress. In this experiment, Azotobacter vinelandii strain DSM85, glycine betaine and proline were used. Inoculated seeds for each variety were placed on Whatman paper in 9 cm Petri dishes containing 15 mL of distilled water or NaCl solutions at various concentrations (control, 100, 200, 300 mM) supplemented with or without glycine betaine (GB) or proline at 5 mM. The results indicated that addition of proline (5 mM) stimulated the production of indol acetic acid and the growth of A. vinelandii at 200 and 300 mM NaCl, respectively. The germination rate index and the germination final percentage decreased significantly (p < 0.05) with increasing salinity level. The germination was significantly diminished at 300 mM with significant variation among varieties and Waha variety had higher germination percentage than Bousselam variety. Inoculation of seeds by A. vinelandii and exogenous application of proline had significantly positive effect on the germination at this concentration of NaCl. The rate of accumulation of Na+ in roots was important at 100 mM and increased at 200 mM. The concentration of K+ decreased when salinity increased. The effect of inoculation or inoculation with proline decreased the accumulation of Na' and reduced the loss of K+ under salt stress. From the present study we can conclude that the use of A. vinelandii strain DSM85 and external application of low concentrations of proline on seeds might be considered as a strategy for the protection of plants under saline stress.

Phase behavior and rheological properties of enzymatically synthesized trehalose decanoate aqueous solutions

Surface tension properties of an enzymatically synthesized equimolar mixture of trehalose mono- and didecanoate in aqueous solutions have been determined. At 20 degrees C a critical micellar concentration (CMC) of 50 micromol/l and a minimal surface tension of 28 mN/m have been obtained. Above the CMC, it has been shown that up to a concentration of 42 wt%, and in a 20-60 degrees C temperature range the sugar ester aqueous solutions do not form any crystalline structure, nor present any phase transition, and the trehalose decanoate molecules form an isotropic worm-like micellar phase. The rheological properties indicate however a more complicated picture in the same concentration and temperature ranges. In steady shear, the viscosity of the trehalose decanoate solutions do not exhibit any shear rate dependence from 1 to 100 s(-1) for concentrations up to 42 wt%. Below 0.8 wt%, the viscosity remains constant and close to that of water; then, between 0.8 and 23 wt%, the viscosity shows a quadratic increase with surfactant concentration. For higher concentrations, up to 42 wt%, no further significant increase in viscosity is observed. In oscillatory shear experiments, the solutions exhibit viscoelastic properties. The observed rheological behavior as a function of concentration and temperature may be due to a progressive evolution of the trehalose decanoate molecular associations: as the concentration increases, the system evolves towards an entangled and/or partially branched or cross-linked micellar network, and eventually a multiconnected network of cross-linked micelles.

Effect of acyl donor chain length and substitutions pattern on the enzymatic acylation of flavonoids

Rutin and esculin were enzymatically acylated with different aliphatic acids as acyl donors (fatty acids, dicarboxylic acids and omega-substituted fatty acids) by an immobilized lipase from Candida antarctica. The effect of the water content and the acyl donors pattern on the flavonoid initial acylation rate and conversion yield were investigated. The obtained results indicated that the water content of the medium has a strong effect on the performance of these reactions. The best conversion yields were reached when the water content was kept lower than 200 ppm. At low water content of the medium, these syntheses are influenced by carbon chain length and substitution pattern of the acyl donors. Higher conversion yields of esculin and rutin (>70%) were obtained with aliphatic acids having high carbon chain length (>12). Moreover, it has been found that the amine and thiol groups on omega-substituted fatty acid chain were unfavourable to these reactions. The 1H NMR and 13C NMR analyses of some synthesized esters (esculin and rutin palmitate) show that only monoesters were produced and that the esterification takes place on the primary OH of glucose moiety of the esculin and on the secondary 4"'-OH of the rhamnose residue of rutin.

Uptake of heavy metals from synthetic aqueous solutions using modified PEI-silica gels

The decontamination of synthetic Pb(II), Zn(II), Cd(II), Ni(II) solutions was investigated, using silica gels chemically modified with poly(ethyleneimine) (PEI) as sorbents. Two families of sorbents, i.e. silica/PEI and crosslinked silica/PEI, were prepared and characterized. Then the removal of metal ions from synthetic aqueous solutions was studied by static tests. They revealed that the sorption capacities depend on the pH, the initial concentration and to some extent on the nature of the metal. The recovery of the metal cations from the saturated sorbents was possible with diluted acid, only for the crosslinked supports. In this case, the regeneration and reuse without sorption decrease, was demonstrated. The presence of other cations (as Na(+), Ca(2+)) and metals does not affect the sorption capacities.

Study of the effects of temperature, pH and yeast extract on growth and exopolysaccharides production by Propionibacterium acidi-propionici on milk microfiltrate using a response surface methodology

AIMS

To study the effects of temperature, pH and yeast extract (YE) concentration on growth and exopolysaccharide (EPS) production by Propionibacterium acidi-propionici DSM 4900 cultivated on milk microfiltrate.

METHODS AND RESULTS

A multifactorial approach using a Response Surface Methodology (RSM) was followed. The results indicated that both growth, and EPS and organic acids production, were influenced by pH, temperature and YE concentration. Biomass and organic acids production occurred in all the tested domains, whereas EPS production was only possible in a narrow pH range (5.3-6.5). The results clearly showed that the optimal conditions for EPS production were different to those for optimal growth. The effect of YE on EPS production was not only due to an increase in growth but also to a direct effect on the production of EPS. The temperature played a major role. A decrease of temperature induced a slowing down of both growth and organic acids production, making the essential factors of the medium and the precursors of EPS biosynthesis more available and hence, leading to an increase in EPS production.

CONCLUSION

The effects of pH, temperature and YE were determined, allowing the definition of favourable, though non-optimal, conditions for EPS production: 23 degrees C, pH 6 and 3 g l(-1) YE concentration.

SIGNIFICANCE AND IMPACT OF THE STUDY

The use of a multifactorial approach for investigating the effect of fermentation conditions on EPS production has been demonstrated.

Exopolysaccharide production by Propionibacterium acidi-propionici on milk microfiltrate

AIMS

The aims of this work were to evaluate growth and exopolysaccharide (EPS) production properties of Propionibacterium acidi-propionici DSM 4900 on milk permeate.

METHODS AND RESULTS

Anaerobic growth on milk permeate was only possible if supplemented with yeast extract (YE). Fermentation capacities of the strain were significantly improved by further increasing the supplemented YE. At 5 g l(-1) YE, consumption of 45 g l(-1) lactose to produce 9 g l(-1) biomass, 34 g l(-1) organic acids and 0.65 g l(-1) EPS was observed. From a kinetic point of view, EPS production occurred during the bacteria growth phase. At the excreted polysaccharide level, the medium showed shear-thinning behaviour with a relatively high apparent viscosity of up to 30 mPa.s (milli.Pascal.second) at a shear rate of 17 s(-1).

CONCLUSION

EPS production by P. acidi-propionici DSM 4900 on milk permeate showed promising rheological behaviour of the milk-derived medium obtained, even at a low production level.

SIGNIFICANCE AND IMPACT OF THE STUDY

A kinetic study on EPS production by a food-grade bacterium that could be used in situ in alimentation was carried out.

High-pressure effects on lysosome integrity and lysosomal enzyme activity in bovine muscle

This study was conducted to determine whether the application of high hydrostatic pressure could modify the enzymatic activity and membrane integrity of lysosomes in muscle. Several combinations of pressure (0-600 MPa) and time (0-300 s) were applied to two types of samples: purified enzymes (cathepsin D and acid phosphatase) in buffer solution and intact muscle (biceps femoris). The enzymes studied showed varying degrees of susceptibility depending on the level of pressure, holding time, and environment. Acid phosphatase activity was minimally affected by pressure in buffer solution, whereas cathepsin D was modulated significantly by the pressure and time applied. The activities of the enzymes extracted from meat increased with pressure. The cytochemical observations showed the presence of primary and secondary lysosomes in muscles. After pressurization, the membrane integrity of the lysosomes was modified. A correlation could be established between lysosomal enzymatic activities and the lysosome membrane breakdown.

Marine macroalgae as a source for osmoprotection for Escherichia coli

At elevated osmolarity of the mineral medium M63, marine macroalgae constitute important osmoprotectants and nutrients sources for Escherichia coli. Growth of bacterial population (16 strains) was improved by supplementing M63 salts medium with either aqueous or ethanolic algal extracts obtained from Ascophyllum nodosum, Fucus serratus, Enteromorpha ramulosa, Ulva lactuca, and Palmaria palmata. In their presence, growth was still observed even at 1.02 M NaCl. Furthermore, the E. coli ZB400 growth in presence of whole macroalgae thalli in M63/0.85 M NaCI reached its maximum within 24 h (5 × 10(7) - 5 × 10(8) colony-forming units [CFU] per milliliter). In the presence of A. nodosum, bacterial growth was inhibited. In the same experimental conditions, ethanolic extracts improved E. coli growth significantly, because the yield reached 10(11) CFU per milliliter. Ulva lactuca and P. palmata allowed the better growth. The Dragendorff-positive compounds extracted from bacterial cells growing on each ethanolic extract exhibited an osmoprotective effect as proved by a disk-diffusion assay. On the other hand, the -onium compounds (quaternary ammonium [betaines] and tertiary sulphonium) and total free amino acid contents of U. lactuca ethanolic extracts were higher than in others. Fucaceae extracts demonstrated especially high protein content. Algal extracts constitute not only an appreciable osmoprotection source for E. coli but also nutrient sources.

Effect of carbonyl cyanide m-chlorophenylhydrazone on Escherichia coli halotolerance

The growth-inhibitory effect of carbonyl cyanide m-chlorophenylhydrazone (CCCP) was less on members of the family Enterobacteriaceae (halotolerant organisms) than it was on species of Vibrio (moderately halophilic organisms). When sodium chloride concentration increased from 0.5 to 0.85 M, this effect was more pronounced for Escherichia coli; it remained relatively stable for Vibrio spp. The effect of carbonyl cyanide m-chlorophenylhydrazone was antagonized by the addition of glycine betaine or proline or by growth in a rich medium.

[Comparative study of the growth of Trichoderma reesei and Penicillium occitanie]

During the last years, a great deal of research on the production of energetic substances was directed to the use of cellulosic by-products. A technique of special interest is the production of fermentissible sugars by the enzymatic hydrolysis of cellulose. Mandels and Reese (1960) showed that a fungi strain of Trichoderma reesei is the best performant microorganism in the production of cellulolytic enzymes. Nevertheless, recent investigation indicated that the rate and the yield of conversion of cellulose to glucose of this strain are limited by its poor beta-glucosidase activity. In order to increase the efficiency of the hydrolytic power of the cellulasic complex two approaches can be considered. Beta-glucosidase enrichment of Trichoderma reesei enzymes. The selection and use of strains with a better performance. In our laboratory, we chose the second approach using Penicillium occitanie comparing it to Trichoderma reesei.