Tunable photoluminescence properties of selenium nanoparticles: biogenic versus chemogenic synthesis

Various technological and biomedical applications rely on the ability of materials to emit light (photoluminescence [PL]), and, among them, metal nanoparticles (NPs) and semi-conductor Quantum Dots (QDs) represent ideal candidates as sensing probes and imaging tools, portraying better PL features than conventional organic dyes. However,theknowledgeofPLbehaviorofsemiconductorNPs – i.e., selenium; SeNPs – is still in its infancy, especially for those synthesized by microorganisms. Considering the essential role played by biogenic SeNPs as antimicrobial, anticancer, and antioxidant agents, or food supplements, their PL properties must be explored to take full advantage of them as eco-friendly and versatile tools. Here, PL features of SeNPs produced by the Se-tolerant Stenotrophomonasmaltophilia SeITE02 strain, compared with chemogenic ones, are investigated, highlighting the PL dependency on the NP size. Indeed, PL emission shifted from indigo-blue (emission wavelength λem 400–450 nm) to green-yellow (λem 480– 570 nm) and orange-red (λem 580–700 nm) for small (ca. 50 nm) and big (ca. 100 nm) SeNPs respectively, revealing the versatility of an environmental bacterial isolate to synthesize diverse PL probes. Besides, biogenic SeNPs show PL lifetime comparable to those of the most used fluorophores, supporting their potential application as markers for (bio)imaging

Influence of bacterial physiology on processing of selenite, biogenesis of nanomaterials and their thermodynamic stability

We explored how Ochrobactrum sp. MPV1 can convert up to 2.5 mM selenite within 120 h, surviving the challenge posed by high oxyanion concentrations. The data show that thiol-based biotic chemical reaction(s) occur upon bacterial exposure to low selenite concentrations, whereas enzymatic systems account for oxyanion removal when 2 mM oxyanion is exceeded. The selenite bioprocessing produces selenium nanomaterials, whose size and morphology depend on the bacterial physiology. Selenium nanoparticles were always produced by MPV1 cells, featuring an average diameter ranging between 90 and 140 nm, which we conclude constitutes the thermodynamic stability range for these nanostructures. Alternatively, selenium nanorods were observed for bacterial cells exposed to high selenite concentration or under controlled metabolism. Biogenic nanomaterials were enclosed by an organic material in part composed of amphiphilic biomolecules, which could form nanosized structures independently. Bacterial physiology influences the surface charge characterizing the organic material, suggesting its diverse biomolecular composition and its involvement in the tuning of the nanomaterial morphology. Finally, the organic material is in thermodynamic equilibrium with nanomaterials and responsible for their electrosteric stabilization, as changes in the temperature slightly influence the stability of biogenic compared to chemogenic nanomaterials

Physical–Chemical Properties of Biogenic Selenium Nanostructures Produced by Stenotrophomonas maltophilia SeITE02 and Ochrobactrum sp. MPV1

Stenotrophomonas maltophilia SeITE02 and Ochrobactrum sp. MPV1 were isolated from the rhizosphere soil of the selenium-hyperaccumulator legume Astragalus bisulcatus and waste material from a dumping site for roasted pyrites, respectively. Here, these bacterial strains were studied as cell factories to generate selenium-nanostructures (SeNS) under metabolically controlled growth conditions. Thus, a defined medium (DM) containing either glucose or pyruvate as carbon and energy source along with selenite () was tested to evaluate bacterial growth, oxyanion bioconversion and changes occurring in SeNS features with respect to those generated by these strains grown on rich media. Transmission electron microscopy (TEM) images show extra- or intra-cellular emergence of SeNS in SeITE02 or MPV1 respectively, revealing the presence of two distinct biological routes of SeNS biogenesis. Indeed, the stress exerted by upon SeITE02 cells triggered the production of membrane vesicles (MVs), which surrounded Se-nanoparticles (SeNPsSeITE02-G_e and SeNPsSeITE02-P_e with average diameter of 179 ± 56 and 208 ± 60 nm, respectively), as highlighted by TEM and scanning electron microscopy (SEM), strongly suggesting that MVs might play a crucial role in the excreting mechanism of the SeNPs in the extracellular environment. On the other hand, MPV1 strain biosynthesized intracellular inclusions likely containing hydrophobic storage compounds and SeNPs (123 ± 32 nm) under pyruvate conditioning, while the growth on glucose as the only source of carbon and energy led to the production of a mixed population of intracellular SeNPs (118 ± 36 nm) and nanorods (SeNRs; average length of 324 ± 89). SEM, fluorescence spectroscopy, and confocal laser scanning microscopy (CLSM) revealed that the biogenic SeNS were enclosed in an organic material containing proteins and amphiphilic molecules, possibly responsible for the high thermodynamic stability of these nanomaterials. Finally, the biogenic SeNS extracts were photoluminescent upon excitation ranging from 380 to 530 nm, whose degree of fluorescence emission (λem = 416–640 nm) was comparable to that from chemically synthesized SeNPs with L-cysteine (L-cys SeNPs). This study offers novel insights into the formation, localization, and release of biogenic SeNS generated by two different Gram-negative bacterial strains under aerobic and metabolically controlled growth conditions. The work strengthens the possibility of using these bacterial isolates as eco-friendly biocatalysts to produce high quality SeNS targeted to possible biomedical applications and other biotechnological purposes

Microbial-Based Bioremediation of Selenium and Tellurium Compounds

The chalcogens selenium (Se) and tellurium (Te) are rare earth elements, which are mainly present in the environment as toxic oxyanions, due to the anthropogenic activities. Thus, the increased presence of these chalcogen-species in the environment and the contamination of wastewaters nearby processing facilities led to the necessity in developing remediation strategies aimed to detoxify waters, soils and sediments. Among the different decontamination approaches, those based on the ability of microorganisms to bioaccumulate, biomethylate or bioconvert Se- and/or Te-oxyanions are considered the leading strategy for achieving a safe and eco-friendly bioremediation of polluted sites. Recently, several technologies based on the use of bacterial pure cultures, bacterial biofilms or microbial consortia grown in reactors with different configurations have been explored for Se- and Te-decontamination purposes. Further, the majority of microorganisms able to process chalcogen-oxyanions have been described to generate valuable Se- and/or Te-nanomaterials as end-products of their bioconversion, whose potential applications in biomedicine, optoelectronics and environmental engineering are still under investigation. Here, the occurrence, the use and the toxicity of Se- and Te-compounds will be briefly overviewed, while the microbial mechanisms of chalcogen-oxyanions bioprocessing, as well as the microbial-based strategies used for bioremediation approaches will be extensively described

Chemogenic versus biogenic synthesis of Selenium nanoparticles: a structural characterization

Among the plethora of available metal- and metalloid-based nanomaterials (NMs), selenium nanostructures (SeNSs) are one of the most interesting from an applicative perspective due to their intermediate properties between metals and non-metals, as well as their high biocompatibility. In this regard, the capability of microorganisms to biotransform toxic Se-oxyanions – i.e., selenite (SeO32-) and selenate (SeO42-) – into their less bioavailable elemental forms [Se(0)], mostly generating Se nanoparticles (SeNPs), represents as a useful and green alternative over chemogenic synthesis allowing to obtain highly thermodynamically stable NMs. However, their structural characterization, in terms of biomolecules and interactions stabilizing the biogenic colloidal solution, is still a black hole in the microbial nanotechnology field, impairing the exploitation of biogenic SeNP full potential. Here, a parallel characterization between biogenic and chemogenic SeNPs was carried out through Fourier Transform Infrared spectroscopy in Attenuated Total Reflectance (ATR-FTIR) mode, Nuclear Magnetic Resonance (NMR) spectroscopy, and Density Functional Theory (DFT) calculations, to better understand which functional groups, hence biomolecules, contribute the most to the stabilization of biogenic SeNPs

Physical–chemical properties of biogenic selenium nanostructures produced by Stenotrophomonas maltophilia SeITE02 and Ochrobactrum sp. MPV1

Stenotrophomonas maltophilia SeITE02 and Ochrobactrum sp. MPV1 were isolated from the rhizosphere soil of the selenium-hyperaccumulator legume Astragalus bisulcatus and waste material from a dumping site for roasted pyrites, respectively. Here, these bacterial strains were studied as cell factories to generate selenium-nanostructures (SeNS) under metabolically controlled growth conditions. Thus, a defined medium (DM) containing either glucose or pyruvate as carbon and energy source along with selenite (www.frontiersin.org) was tested to evaluate bacterial growth, oxyanion bioconversion and changes occurring in SeNS features with respect to those generated by these strains grown on rich media. Transmission electron microscopy (TEM) images show extra- or intra-cellular emergence of SeNS in SeITE02 or MPV1 respectively, revealing the presence of two distinct biological routes of SeNS biogenesis. Indeed, the stress exerted by www.frontiersin.org upon SeITE02 cells triggered the production of membrane vesicles (MVs), which surrounded Se-nanoparticles (SeNPsSeITE02-G_e and SeNPsSeITE02-P_e with average diameter of 179 ± 56 and 208 ± 60 nm, respectively), as highlighted by TEM and scanning electron microscopy (SEM), strongly suggesting that MVs might play a crucial role in the excreting mechanism of the SeNPs in the extracellular environment. On the other hand, MPV1 strain biosynthesized intracellular inclusions likely containing hydrophobic storage compounds and SeNPs (123 ± 32 nm) under pyruvate conditioning, while the growth on glucose as the only source of carbon and energy led to the production of a mixed population of intracellular SeNPs (118 ± 36 nm) and nanorods (SeNRs; average length of 324 ± 89). SEM, fluorescence spectroscopy, and confocal laser scanning microscopy (CLSM) revealed that the biogenic SeNS were enclosed in an organic material containing proteins and amphiphilic molecules, possibly responsible for the high thermodynamic stability of these nanomaterials. Finally, the biogenic SeNS extracts were photoluminescent upon excitation ranging from 380 to 530 nm, whose degree of fluorescence emission (λem = 416–640 nm) was comparable to that from chemically synthesized SeNPs with L-cysteine (L-cys SeNPs). This study offers novel insights into the formation, localization, and release of biogenic SeNS generated by two different Gram-negative bacterial strains under aerobic and metabolically controlled growth conditions. The work strengthens the possibility of using these bacterial isolates as eco-friendly biocatalysts to produce high quality SeNS targeted to possible biomedical applications and other biotechnological purposes

Efectos del clima y el nivel del agua sobre la reproducción de aves acuáticas coloniales en Laguna Mar Chiquita - Bañados del Río Dulce (Argentina Central)

En el presente trabajo se exploró la relación entre factores relacionados al clima y la reproducción de aves acuáticas coloniales en un extenso humedal del centro de Argentina, el sistema Laguna Mar Chiquita - Bañados del Río Dulce. Debido a sus distintos requerimientos ecológicos, las diversas especies presentaron respuestas disímiles a las variaciones de los factores climáticos, los cuales a su vez actúan a distintas escalas espaciales. El éxito reproductivo de casi todas las especies fue negativamente afectado por el viento durante las tormentas que se forman localmente durante el verano. Las variaciones en el nivel del agua, producidas por fenómenos no locales sino ocurridos en la parte alta de la cuenca, a gran distancia del humedal, tuvieron una acción directa sobre el número de especies en colonias. El número de parejas, en cambio, no fue directamente afectado por dichas variaciones, aunque el número de parejas en colonias de la Garcita Azulada (Butorides striata) estuvo relacionado al área de hábitat óptimo disponible para la alimentación y nidificación de esta especie, superficie que en definitiva fue regulada por el nivel del agua. La formación de colonias de aves acuáticas estuvo supeditada a niveles estables o con variaciones de hasta 1 m entre un año y el siguiente. Los datos obtenidos presentan implicancias para la biología de la conservación y las estrategias de manejo del agua.The relationship between climate-related factors in an important extensive wetland of central Argentina (Laguna Mar Chiquita - Bañados del Río Dulce) and colonial waterbirds reproduction was explored. Due to their different ecological requirements, the diverse species responded differently to variations in climatic factors, which in turn interact at different spatial scales. Nesting success of almost all species was negatively affected by storm winds occurring in the region in summer. Water level changes, induced by non-local phenomena occurring in the high basin, at a great distance from the Mar Chiquita– Dulce River system, had a direct effect on species number in colonies. On the contrary, pair numbers was not directly affected by water level changes, although the pair numbers in the Striated Heron (Butorides striata) colonies was related to the area of the feeding and nesting habitat suitable for this species, which was eventually regulated by water level. Waterbirds colony formation depended on water levels that were stable or changed in up to 1 m in consecutive years. The data obtained has implications for biodiversity conservation and water management strategies.Fil: Torres, Ricardo Marcelo. Universidad Nacional de Córdoba; ArgentinaFil: Michelutti, Matias Pablo. No especifica;Fil: Dominino, Jael. Administración Nacional de Parques; ArgentinaFil: León, José Gabriel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Mangeaud, Arnaldo. Universidad Nacional de Córdoba; ArgentinaFil: Rodriguez, Andres. Universidad Nacional de Córdoba; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Pozzi Piacenza, Cecilia Elena. Universidad Nacional de Córdoba; ArgentinaFil: Plencovich, Gonzalo. Universidad Nacional de Córdoba; ArgentinaFil: Pagot, Mariana. Universidad Nacional de Córdoba; ArgentinaFil: Hillman, Gerardo. Universidad Nacional de Córdoba; Argentin

Polysaccharide-based biodegradable films for agricultural mulching

In the last 20 years, the global population has blowout growth from 6.0 billion to 7.2 billion and will reach over 8.0 billion around 2046 [1]. Consequently, food shortage has drawn attention, and the demand for agricultural products has increased annually. To meet this need, the excessive and prolonged use of mulching films based on low-density polyethene resulted in significant environmental pollution events, leading to serious side effects on human health [2]. Due to the thickness of the plastic film and the difficulty of recovery, some mulch films were discarded in agricultural soils intentionally or unintentionally. Mulch film residue is a direct source of farmland meso- and microplastics (MMPs), which constitute a global environmental issue, as they accumulate even in the food chain [3]. MMPs' further degradation into nanoscale particles can endanger human health [4]. To provide agricultural sustainability, there is a great interest in developing biodegradable bio-based polymeric films for agriculture mulching, which can be tilled directly into the soil after use. Based on the above issues, this study aims at (i) the preparation and characterisation of biodegradable bio-based composite films and (2) their enrichment with plant nutrients, which could be efficiently released into the water to sustain their application as mulch films on the soil. Sodium carboxymethyl cellulose (CMC), chitosan (CS) and sodium alginate (SA) were combined in the presence of glycerol as a plasticiser to produce composite films by solvent casting. Composition (i.e., concentrations and mass ratios between the precursors) and cross-linking agent (CaCl2) effects on films' properties were evaluated. In the first stage, we investigated the structure of the formed films through Attenuated Total Reflection Fourier Transform Infrared (ATR-FTIR) spectroscopy, the thermal and mechanical properties by thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA), and some water-interaction properties (degree of swelling and solubility in water). This approach allowed identifying the best quality films, which were enriched with NH4H2PO4, as N and P are generally the most deficient nutrients in the soil. Moreover, the release kinetics in the water of this salt was studied. The latter aspect is of great importance as the release of N and P helps to improve the nutrient supply to the soil, thus reducing the use of synthetic fertilisers. [1] B. Chieng et al. J. Appl. Polym. Sci. 130 (2013) 4576-4580 [2] H. M. S . Akhtar, et al. Int. J. Biol. Macromol. 118 (2018), 469-477 [3] M.C. Rillig, M. C. Environ. Sci. Technol. 46 (2012), 6453-6454 [4] I. Ali et al. J. Clean. Prod. 313 (2021) 12786

The actinomycete Kitasatospora sp. SeTe27, subjected to adaptive laboratory evolution (ALE) in the presence of selenite, varies its cellular morphology, redox stability, and tolerance to the toxic oxyanion

The effects of oxyanions selenite (SeO32−) in soils are of high concern in ecotoxicology and microbiology as they can react with mineral particles and microorganisms. This study investigated the evolution of the actinomycete Kitasatospora sp. SeTe27 in response to selenite. To this aim, we used the Adaptive Laboratory Evolution (ALE) technique, an experimental approach that mimics natural evolution and enhances microbial fitness for specific growth conditions. The original strain (wild type; WT) isolated from uncontaminated soil gave us a unique model system as it has never encountered the oxidative damage generated by the prooxidant nature of selenite. The WT strain exhibited a good basal level of selenite tolerance, although its growth and oxyanion removal capacity were limited compared to other environmental isolates. Based on these premises, the WT and the ALE strains, the latter isolated at the end of the laboratory evolution procedure, were compared. While both bacterial strains had similar fatty acid profiles, only WT cells exhibited hyphae aggregation and extensively produced membrane-like vesicles when grown in the presence of selenite (challenged conditions). Conversely, ALE selenite-grown cells showed morphological adaptation responses similar to the WT strain under unchallenged conditions, demonstrating the ALE strain improved resilience against selenite toxicity. Whole-genome sequencing revealed specific missense mutations in genes associated with anion transport and primary and secondary metabolisms in the ALE variant. These results were interpreted to show that some energy-demanding processes are attenuated in the ALE strain, prioritizing selenite bioprocessing to guarantee cell survival in the presence of selenite. The present study indicates some crucial points for adapting Kitasatospora sp. SeTe27 to selenite oxidative stress to best deal with selenium pollution. Moreover, the importance of exploring non-conventional bacterial genera, like Kitasatospora, for biotechnological applications is emphasized