Grapevine berry skin is a complex structure that contributes to the final size and shape of the fruit and affects its quality traits. The organization of cell wall polysaccharides in situ and their modification during ripening are largely uncharacterized.

Bacteria have developed different mechanisms for the transformation of metalloid oxyanions to non-toxic chemical forms. A number of bacterial isolates so far obtained in axenic culture has shown the ability to bioreduce selenite and tellurite to the elemental state in different conditions along with the formation of nanoparticles—both inside and outside the cells—characterized by a variety of morphological features. This reductive process can be considered of major importance for two reasons: firstly, toxic and soluble (i.e. bioavailable) compounds such as selenite and tellurite are converted to a less toxic chemical forms (i.e. zero valent state); secondly, chalcogen nanoparticles have attracted great interest due to their photoelectric and semiconducting properties. In addition, their exploitation as antimicrobial agents is currently becoming an area of intensive research in medical sciences. In the present study, the bacterial strain Ochrobactrum sp. MPV1, isolated from a dump of roasted arsenopyrites as residues of a formerly sulfuric acid production near Scarlino (Tuscany, Italy) was analyzed for its capability of efficaciously bioreducing the chalcogen oxyanions selenite (SeO3 2−) and tellurite (TeO3 2−) to their respective elemental forms (Se0 and Te0) in aerobic conditions, with generation of Se- and Te-nanoparticles (Se- and TeNPs). The isolate could bioconvert 2 mM SeO3 2− and 0.5 mM TeO3 2− to the corresponding Se0 and Te0 in 48 and 120 h, respectively. The intracellular accumulation of nanomaterials was demonstrated through electron microscopy. Moreover, several analyses were performed to shed light on the mechanisms involved in SeO3 2− and TeO3 2− bioreduction to their elemental states. Results obtained suggested that these oxyanions are bioconverted through two different mechanisms in Ochrobactrum sp. MPV1. Glutathione (GSH) seemed to play a key role in SeO3 2− bioreduction, while TeO3 2− bioconversion could be ascribed to the catalytic activity of intracellular NADH-dependent oxidoreductases. The organic coating surrounding biogenic Se- and TeNPs was also characterized through Fourier-transform infrared spectroscopy. This analysis revealed interesting differences among the NPs produced by Ochrobactrum sp. MPV1 and suggested a possible different role of phospholipids and proteins in both biosynthesis and stabilization of such chalcogen-NPs. In conclusion, Ochrobactrum sp. MPV1 has demonstrated to be an ideal candidate for the bioconversion of toxic oxyanions such as selenite and tellurite to their respective elemental forms, producing intracellular Se- and TeNPs possibly exploitable in biomedical and industrial applications.

The evaluation of cell parietal components of yeasts is an important criterium for the selection of wine starters since they play a key role in the vinification process. The aim of this study was to characterize and compare the cell wall composition of four industrial (BM45, D47, EC1118, K1) and three native Saccharomyces cerevisiae (MY8, MY11, PEDRO2000E) wine strains by means of scanning and transmission electron microscopy and ATR-FTIR microspectroscopy. A statistically significant variability in the cell wall thickness and cell diameter was observed among the yeast cells, with native strains showing higher cell diameter values. FTIR microspectroscopy applied on the intact cells without any previous invasive treatment and on the separated cell walls highlighted profound differences among the strains in terms of the overall content of parietal polysaccharides as related to the thickness of the cell walls and in terms of the relative concentration of β-glucans and mannans in the cell walls. The strains EC1118, MY11, and PEDRO2000E showed a higher overall content of β-glucans and mannans, whose lower relative concentration in PEDRO2000E was compensated by a thicker cell wall; BM45 and D47 were characterized by a high relative concentration of polysaccharides in a thinner wall, while K1 and MY8 displayed a low relative concentration of polysaccharides. ATR-FTIR microspectroscopy allows identifying polysaccharide-rich yeast strains and can become a smart option for the selection of starter cultures to be used in oenology and for other applications in food industry, thanks to the interesting technological properties of parietal polysaccharides. Graphical Abstract

The role of virtual simulations in the evolution of primary school students' mental models about electrostatics is investigated by analysing the answers of two groups of 9–10 years old pupils inside instructional sequences that combine two hands-on activities using balloons and jackets with the same activities using PhET simulations: one group followed a sequence where the real experiments were conducted before the virtual simulations, the other group followed a sequence where the virtual simulations where proposed before the real experiments. Students’ answers were categorized into a descriptive dimension (accordance with the phenomena) and into an explanatory dimension (level of adequacy with the microscopic model based on elementary charges). Our results show that, although virtual simulations improve the level of adequacy of students' answers to the target model, this improvement is not transferred to new phenomena, so that the capability of relating the developed model to the real world is the same in both sequences. Moreover, about 40% of pupils remained at their starting non-explanatory level in both teaching sequences. We conclude that simulations per se do not help students in evaluating and refining their models, indicating the need for teachers’ support in modelling-based instruction involving not visible physical entities.