Biogenic metal/metalloid nanoparticles of microbial origin retain a functional biomolecular capping layer that confers structural stability. Little is known about the composition of such capping material. In this study, selenium nanoparticles (SeNPs) synthesized by five different bacterial strains underwent comparative analysis with newly proposed protocols for quantifying the concentration of carbohydrates, proteins and lipids present in capping layers. SeNPs were therefore treated with two different detergents to remove portions of the surrounding caps in order to assess the resulting effects. Capping material quantification was carried out along with the measure of parameters such as hydrodynamic diameter, polydispersity and surface charge. SeNPs from the five strains showed differences in their distinct biomolecule ratios. On the other hand, structural changes in the nanoparticles induced by detergents did not correlate with the amounts of capping matrix removed. Thus, the present investigation suggests a hypothesis to describe capping layer composition of the bacterial SeNPs: some biomolecules are bound more strongly than others to the core metalloid matrix, so that the diverse capping layer components differentially contribute to the overall structural characteristics of the nanoparticles. Furthermore, the application of the approach here in combining quantification of cap-associated biomolecules with the measurement of structural integrity-related parameters can give the biogenic nanomaterial field useful information to construct a data bank on biogenically synthesized nanostructures.

Fruits of the sweet cherry (Prunus avium L.) accumulate a range of antioxidants that can help to prevent cardiovascular disease, inflammation and cancer. We tested the in vitro antioxidant activity of 18 sweet cherry cultivars collected from 12 farms in the protected geographical indication region of Marostica (Vicenza, Italy) during two growing seasons. Multiple targeted and untargeted metabolomics approaches (NMR, LC-MS, HPLC-DAD, HPLC-UV) as well as artificial simplified phytocomplexes representing the cultivars Sandra Tardiva, Sandra and Grace Star were then used to determine whether the total antioxidant activity reflected the additive effects of each compound or resulted from synergistic interactions. We found that the composition of each cultivar depended more on genetic variability than environmental factors. Furthermore, phenolic compounds were the principal source of antioxidant activity and experiments with artificial simplified phytocomplexes indicated strong synergy between the anthocyanins and quercetins/ascorbic acid specifically in the cultivar Sandra Tardiva. Our data therefore indicate that the total antioxidant activity of sweet cherry fruits may originate from cultivar-dependent interactions among different classes of metabolite.

Abstract. The exploitation of biological systems (i.e. plants, fungi and bacteria) for the production of nanomaterials relies on their ability to bioconvert toxic metal(loid) ions into their less toxic and bioavailable elemental states forming mainly nanoparticles (NPs) or nanorods (NRs). Further, these methods of nanomaterial production are nowadays recognized as eco-friendly alternatives to the chemical synthesis processes. A common feature among the so-called biogenic nanomaterials is the presence of an organic layer surrounding them. However, we are just learning the existing relation between biogenic nanostructures and their organic material. Our work is focused on the study of bacterial strains for the production of selenium nanoparticles (SeNPs) as end product of selenite (SeO 3 2-) bioconversion. In this context, our previous reports described the ability of two bacteria, namely Bacillus mycoides SelTE01 and Stenotrophomonas maltophilia SelTE02, to generate SeNPs, which were surrounded by organic material. Here, the potential role of this organic material as stabilizing agent of SeNPs was investigated altering both the bacteria cells culturing and the SeNPs extraction procedure, in order to understand the interaction between these two elements in suspension. As a result, SeNPs produced by both bacterial strains showed the tendency to aggregate when subjected to the treatments tested, suggesting an involvement of the surrounding organic material in their stabilization in suspension.

Extended AbstractSelenium nanoparticles (SeNPs), which range in size from 50 to 300 nm, show broad applications such as antioxidant, immunoprotective, anti-tumor, antimicrobial and antobiofilm activities [1]. They also can be exploited in bioremediation, production of quantum dots and biosensors.SeNPs can be synthesized chemically (ChSeNPs) or biologically (BioSeNPs). BioSeNPs can be obtained by various microorganisms, plant extracts or enzymatic preparations. Biosynthesis offers advantages over chemical synthesis such as minor costs, absence of toxic by products and energy saving (i.e. carried out under mild environmental conditions). BioSeNPs also present an outer layer, mainly consisting of a proteinaceous material, that seems to greatly influence the reactivity of SeNPs in terms of antimicrobial and antibiofilm effects. It has been proved that antimicrobial activity of BioSeNPs is significantly more than ChSeNPs.To better understand possible mechanisms of this antimicrobial/antibiofilm efficacy of BioSeNPs, the nature of their outer layer should be characterized in details. In fact, the description of such surface-associated proteins and specificity of their binding to metal nanoparticles might allow to formulate new hypotheses on the biosynthetic route of SeNPs. Likely, nanoparticle-associated proteins are involved in the synthesis and maturation of SeNPs themselves.This study focuses on the proteomic characterization of BioSeNPs external layer. For biogenic production of SeNPs, we used Bacillus mycoides SeITE01, an environmental strain isolated from the selenium-hyperaccumulator legume Astragalus bisulcatus rizosphere, capable of tolerating up to 25mM selenite [2].The first step of the research was the characterization of protein associated to BioSeNPs through SDS-PAGE and mass spectrometry after 24 hours growth in the presence of selenite. Moreover, we studied the specificity of the protein-NP bond. Since ChSeNPs can also bind proteins when exposed to a cell free protein extract, a comparison between proteins associated to BioSeNPs and exposed ChSeNPs is currently ongoing.We identified BioSeNPs-associated proteins for B. mycoides, which belong to primary and secondary metabolism, especially protein and amino acid metabolisms. As expected, proteins capable of reductase activity were found which are possibly involved in selenite reduction to zero-valent SeNPs: pyridine-nucleotide disulphide oxidoreductase, enoyl-ACP reductase (fatty acid biosynthesis) and FMN-dependent NADH azoreductase. Some membrane transporter and proteins involved in cell wall metabolism were also found, such as: penicillin-binding protein and lysozyme (peptidoglycan synthesis and degradation pathways, respectively) and ABC transporters. Several proteins involved in polypeptide synthesis and aminoacid metabolism were identified including: elongation factors Tu and G, ribosomal proteins, peptidases and a protease; glutamate and alanine dehydrogenases. Some of these are also involved in the sporulation process: elongation factors, ATPase, ...