Differential physiological responses of a biogenic silver nanoparticle and its production matrix silver nitrate in Sorghum bicolor.

Silver nanoparticles (AgNP) have been extensively applied in different industrial areas, mainly due to their antibiotic properties. One of the environmental concerns with AgNP is its incorrect disposal, which might lead to severe environmental pollution. The interplay between AgNP and plants is receiving increasing attention. However, little is known regarding the phytotoxic effects of biogenic AgNP on terrestrial plants. This study aimed to compare the effects of a biogenic AgNP and AgNO3 in Sorghum bicolor seedlings. Seeds were germinated in increasing concentrations of a biogenic AgNP and AgNO3 (0, 10, 100, 500, and 1000 µM) in a growth chamber with controlled conditions. The establishment and development of the seedlings were evaluated for 15 days. Physiological and morpho-anatomical indicators of stress, enzymatic, and non-enzymatic antioxidants and photosynthetic yields were assessed. The results showed that both AgNP and AgNO3 disturbed germination and the establishment of sorghum seedlings. AgNO3 released more free Ag+ spontaneously compared to AgNP, promoting increased Ag+ toxicity. Furthermore, plants exposed to AgNP triggered more efficient protective mechanisms compared with plants exposed to AgNO3. Also, the topology and connectivity of the correlation-based networks were more impacted by the exposure of AgNO3 than AgNP. In conclusion, it is plausible to say that the biogenic AgNP is less toxic to sorghum than its matrix AgNO3.

Differential physiological responses of a biogenic silver nanoparticle and its production matrix silver nitrate in Sorghum bicolor

Silver nanoparticles (AgNP) have been extensively applied in different industrial areas, mainly due to their antibiotic properties. One of the environmental concerns with AgNP is its incorrect disposal, which might lead to severe environmental pollution. The interplay between AgNP and plants is receiving increasing attention. However, little is known regarding the phytotoxic effects of biogenic AgNP on terrestrial plants. This study aimed to compare the effects of a biogenic AgNP and AgNO3 in Sorghum bicolor seedlings. Seeds were germinated in increasing concentrations of a biogenic AgNP and AgNO3 (0, 10, 100, 500, and 1000 μM) in a growth chamber with controlled conditions. The establishment and development of the seedlings were evaluated for 15 days. Physiological and morpho-anatomical indicators of stress, enzymatic, and non-enzymatic antioxidants and photosynthetic yields were assessed. The results showed that both AgNP and AgNO3 disturbed germination and the establishment of sorghum seedlings. AgNO3 released more free Ag+ spontaneously compared to AgNP, promoting increased Ag+ toxicity. Furthermore, plants exposed to AgNP triggered more efficient protective mechanisms compared with plants exposed to AgNO3. Also, the topology and connectivity of the correlation-based networks were more impacted by the exposure of AgNO3 than AgNP. In conclusion, it is plausible to say that the biogenic AgNP is less toxic to sorghum than its matrix AgNO3.

A new strain of Aspergillus tubingensis for high-activity pectinase production.

Pectinase is a general term for a class of enzymes that decompose pectin. To obtain a fungal strain with high-activity pectinase of potential commercial importance, we screened microorganisms from the soil of vineyards, performed mutation breeding by ultraviolet (UV) and nitrosoguanidine (NTG) mutagenesis, and performed comparisons to commercially available pectinases. We found that the derived pectinase-producing strain Rn14-88A had the highest pectinase activity of 8363.215 U/mL, and identified it using internal transcribed spacer sequence analysis as Aspergillus tubingensis. Rn14-88A was the original strain for UV mutagenesis, from which mutant strain R-7-2-4 had the highest pectinase enzyme activity (9198.68 U/mL), which was a 9.99% increase compared to that of Rn14-88A. Following NTG mutagenesis of R-7-2-4, mutant strain Y1-3-2-6 had a pectinase enzyme activity of 9843.34 U/mL, which reflects a 6.36% increase compared to the pectinase activity of R-7-2-4. Subsequently, another round of NTG mutagenesis was performed on Y1-3-2-6, and the mutagenic strain Y2-6-3-4 exhibited an improved enzyme activity of 21,864.34 U/mL, which was 161.44% higher than that of Rn14-88A. Through liquid fermentation experiments of A. tubingensis Y2-6-3-4, it was determined that pectinase activity was the highest at a fermentation time of 20 h. Therefore, we conclude that A. tubingensis Y2-6-3-4 has potential for use in commercial production.

Identification of Aspergillus tubingensis in a primary skin infection.

OBJECTIVE: Aspergillus section Nigri comprises a group of related species that include Aspergillus niger, A. welwitschiae, A. carbonarius, A. brasiliensis and A. tubingensis. Some of these species are morphologically very similar to A. niger but exhibit different patterns of susceptibility to antifungal agents; such is the case for A. tubingensis. Therefore, when diagnosing aspergillosis, it is important to identify the pathogen at the species level. This study aimed to identify the species of an Aspergillus spp. isolate (MM-82) obtained from a patient with a dermatosis localized to the right leg. MATERIALS AND METHODS: The MM-82 isolate was examined for macro- and microscopic morphology, conidia size and thermotolerance, and a phylogenetic analysis of a benA gene segment was performed for molecular identification. Susceptibility to antifungals was determined using antifungal microdilution according to the methodology of European Society of Clinical Microbiology and Infectious Diseases (EUCAST). RESULTS: Based on its phenotypic characteristics and the phylogenetic analysis of the sequence of a benA gene segment, the MM-82 isolate was identified as A. tubingensis. This fungus did not show resistance to antifungal agents commonly used for treatment. CONCLUSION: This study demonstrated that A. tubingensis can cause skin infection; this constitutes the first report of a case of aspergillosis caused by A. tubingensis in Mexico.

Elucidating Protein Involvement in the Stabilization of the Biogenic Silver Nanoparticles.

Silver nanoparticles (AgNPs) have been broadly used as antibacterial and antiviral agents. Further, interests for green AgNP synthesis have increased in recent years and several results for AgNP biological synthesis have been reported using bacteria, fungi and plant extracts. The understanding of the role and nature of fungal proteins, their interaction with AgNPs and the subsequent stabilization of nanosilver is yet to be deeply investigated. Therefore, in an attempt to better understand biogenic AgNP stabilization with the extracellular fungal proteins and to describe these supramolecular interactions between proteins and silver nanoparticles, AgNPs, produced extracellularly by Aspergillus tubingensis-isolated as an endophytic fungus from Rizophora mangle-were characterized in order to study their physical characteristics, identify the involved proteins, and shed light into the interactions among protein-NPs by several techniques. AgNPs of around 35 nm in diameter as measured by TEM and a positive zeta potential of +8.48 mV were obtained. These AgNPs exhibited a surface plasmon resonance (SPR) band at 440 nm, indicating the nanoparticles formation, and another band at 280 nm, attributed to the electronic excitations in tryptophan, tyrosine, and/or phenylalanine residues in fungal proteins. Fungal proteins were covalently bounded to the AgNPs, mainly through S-Ag bonds due to cysteine residues (HS-) and with few N-Ag bonds from H2N- groups, as verified by Raman spectroscopy. Observed supramolecular interactions also occur by electrostatic and other protein-protein interactions. Furthermore, proteins that remain free on AgNP surface may perform hydrogen bonds with other proteins or water increasing thus the capping layer around the AgNPs and consequently expanding the hydrodynamic diameter of the particles (~264 nm, measured by DLS). FTIR results enabled us to state that proteins adsorbed to the AgNPs did not suffer relevant secondary structure alteration upon their physical interaction with the AgNPs or when covalently bonded to them. Eight proteins in the AgNP dispersion were identified by mass spectrometry analyses. All these proteins are involved in metabolic pathways of the fungus and are important for carbon, phosphorous and nitrogen uptake, and for the fungal growth. Thereby, important proteins for fungi are also involved in the formation and stabilization of the biogenic AgNPs.

Statistical optimization for tannase production by Aspergillus tubingensis in solid-state fermentation using tea stalks

Background A sequential statistical strategy was used to optimize tannase production from Aspergillus tubingensis using tea stalks by solid-state fermentation. Results First, using a Plackett-Burman design, inoculum size and incubation time (among seven tested variables) were identified as the most significant factors for tannase yield. The effects of significant variables were further evaluated through a single steepest ascent experiment and central composite design with response surface analysis. Under optimal conditions, the experimental value of 84.24 units per gram of dry substrate (U/gds) closely matched the predicted value of 87.26 U/gds. Conclusions The result of the statistical approach was 2.09 times higher than the basal medium (40.22 U/gds). The results were fitted onto a second-order polynomial model with a correlation coefficient (R²) of 0.9340, which implied an adequate credibility of the model.