This work discusses the self-assembly properties of thermoresponsive hybrid oligosaccharide-block-poly(N-isopropylacrylamide) copolymer systems: maltoheptaose-block-poly(N-isopropylacrylamide) (Mal(7)-b-PNIPAM(n)) copolymers. Those systems at different molar masses and volume fractions were synthesized using Cu(I)-catalyzed 1,3-dipolar azide/alkyne cycloaddition, so-called "click" chemistry, between an alkynyl-functionalized maltoheptaose (1) and poly(N-isopropylacrylamide) having a terminal azido group (N(3)-PNIPAM(n)) prepared by atom transfer radical polymerization (ATRP). While the cloud point (T(cp)) of the N(3)-PNIPAM(n) ranged from 36.4 to 51.5 degrees C depending on the degree of polymerization, those obtained of the diblock copolymers ranged from 39.4 to 73.9 degrees C. The self-assembly of such systems is favored due to the hydrophobicity of the PNIPAM in water above the T(cp). While the N(3)-PNIPAM(n) present polydisperse globular shape with a mean diameter of 500 nm, well-defined vesicular morphologies with an approximate diameter of 300 nm are obtained in diblock copolymer systems. These results were obtained and confirmed using static and dynamic light scattering as well as imaging techniques such as transmission electron microscope experiments.

Ralstonia metallidurans CH34 (formerly Alcaligenes eutrophus CH34) is a soil bacterium characteristic of metal-contaminated biotopes, as it is able to grow in the presence of a variety of heavy metals. R. metallidurans CH34 is reported now to resist up to 6 mM selenite and to reduce selenite to elemental red selenium as shown by extended X-ray absorption fine-structure analysis. Growth kinetics analysis suggests an adaptation of the cells to the selenite stress during the lag-phase period. Depending on the culture conditions, the medium can be completely depleted of selenite. Selenium accumulates essentially in the cytoplasm as judged from electron microscopy and energy-dispersive X-ray analysis. Elemental selenium, highly insoluble, represents a nontoxic storage form for the bacterium. The ability of R. metallidurans CH34 to reduce large amounts of selenite may be of interest for bioremediation processes targeting selenite-polluted sites.In aerated environments, selenium can exist in several redox forms, including the elemental form, Se(0), which is a solid, and the oxidized forms, selenite (SeO 3 2Ϫ ) and selenate (SeO 4 2Ϫ ), which are bioavailable, mobile, and toxic for many organisms (5). Selenium is widely distributed in virtually all materials of the earth's crust, but accumulation of toxic compounds of selenium can also have an anthropogenic source. Selenium and its derivatives are widely used in industrial products, and the problem of selenium accumulation remains in mind after the ecological disaster of Kesterson National Wildlife Refuge, in California, due to agricultural drainage released in the Kesterson Reservoir (19). Since microorganisms are involved in the geochemical cycle of selenium, soil bacteria may thus be used in bioremediation processes. Some of them are able to resist high concentrations of a variety of metals and oxyanions (16), and the reduction of selenite to selenium by the common aerobic soil bacterium Bacillus subtilis (10) or the phototrophic purple nonsulfur bacterium Rhodospirillum rubrum (12) has been reported. The accumulation of selenium by Rhodobacter sphaeroides has been also reported very recently (23).Ralstonia metallidurans CH34 (formerly Alcaligenes eutrophus CH34) is a microorganism characteristic of metal-contaminated biotopes (14 . Resistance is due mainly to plasmid-mediated efflux followed by postefflux events such as bioprecipitation or biological sequestration (1, 7). In this report, the ability of R. metallidurans CH34 to resist also selenite is described for the first time. The physiological and morphological changes resulting from the presence of selenite in the culture medium were studied by using direct chemical assay for selenite, electron microscopy, and electron-dispersive X-ray analysis. The speciation of selenium was determined by X-ray absorption spectroscopy techniques. MATERIALS AND METHODSStrain and growth media. R. metallidurans CH34 was grown under aerobic conditions at 29°C in the minimal mineral medium described in reference 15. As this medium ...