Pyrite biomining proficiency of sulfur dioxygenase (SDO) enzyme extracted from Acidithiobacillus thiooxidans

Isolation of a putative sulfur comproportionating microorganism

Sulfur comproportionation, the coupled oxidation of sulfide and reduction of sulfate to elemental sulfur, is a heretofore undiscovered microbial catabolism that has been predicted based on thermodynamic calculations. Here, we report the isolation of an Acidithiobacillus thiooxidans strain that grew to cell densities of > 107 cells mL-1 in autotrophic sulfur comproportionation medium. It was isolated from extremely low pH snottite biofilms in the sulfidic karst at Frasassi, Italy. The organism's genome sequence revealed the presence of numerous genes involved in sulfur transformations that could be linked in a sulfur comproportionation pathway. Future investigations of this novel link in the biogeochemical sulfur cycle could include monitoring of the concentrations of sulfate, sulfide, and elemental sulfur during growth to learn whether they are consistent with stoichiometric ratios expected for sulfur comproportionation. In addition, stable and radioisotope incubations coupled with NanoSIMS, scintillation counting, and isotope ratio mass spectrometry should reveal that sulfate and sulfide are coupled in a single catabolic reaction to produce elemental sulfur.

Copper recovery from waste printed circuit boards using pyrite as the bioleaching substrate

Waste printed circuit boards (WPCBs) can be bioleached for Cu recovery, but lack of substrate for the bioleaching culture. In this study, using pyrite as a bacterial substrate for bioleaching WPCBs and recovering Cu was explored. The results showed that the WPCBs bioleaching using pyrite as the bacterial substrate was feasible. Mechanical crushing was a suitable WPCBs pretreatment method. The optimal WPCBs and pyrite pulp densities were respectively found to be 1.25% (w/v) and 1.0% (w/v), and the suitable nitrogen source ratio ((NH4)2SO4: (NH4)2HPO4) was deemed as 2 g/L: 2 g/L, achieving a Cu2+ leaching efficiency of 95.60 ± 1.57% in 14 d. Copper in the bioleaching solution can be directly recovery via electrodeposition. The Cu recovery efficiency in 60 min was up to 92.19 ± 1.35% under the optimal condition that the initial Cu2+ concentration and pH were respectively set at 7.34 g/L and 2.75, and the current density was set at 200 A/m2. Copper was found as the dominant metal in the cathode deposits, existing in the form of Cu and Cu2O. This work provided a novel approach for bioleaching WPCBs and recovering Cu.

Bioremediation competence of Aspergillus flavus DDN on pond water contaminated by mining activities

This research was performed to evaluate the possibilities of reducing the physicochemical properties of polluted pond water situated around the magnesite mine tailing through indigenous metal tolerant fungi. The physicochemical analysis results revealed that most of the physicochemical properties of pond water sample were crossing the permissible limits. From the muddy pond soil sample, Aspergillus flavus DDN was identified (through molecular characterization) as predominant metal tolerant fungal strain and it showed resistance to Cr(VI), Pb(II), Zn(II), Cd(II), and Mg(IV) up to 1000 μg mL^-1 concentrations. This strain also effectively reduced (through biosorption) these metals in a short duration of the bioremediation process. In a lab-scale bioremediation study, the A. flavus DDN significantly reduced most of the physicochemical parameters crossing the permissible limit in polluted pond water in the presence of FM1 minimal media in 10 days of incubation. The dissolved oxygen level was significantly increased up to 74.91% from 5.86 ± 0.39 to 10.25 ± 0.95 in 10 days of treatment. The metal reduction and other physicochemical properties reduction were directly related to the biomass of A. flavus DDN. These findings suggest that A. flavus DDN can remove pollutants from magnesite mine tailing polluted pond water because elevated fungal biomass resulted in the highest percentage of pollutant reduction from the sample.

Sustainable bioremediation approach to treat the sago industry effluents and evaluate the possibility of yielded biomass as a single cell protein (SCP) using cyanide tolerant Streptomyces tritici D5

This sustainable approach was performed to evaluate the bioremediation potential of cyanide resistant bacterial species on sago industry effluents and assess the possibility of using the yielded biomass as single cell protein (SCP). The predominant cyanide tolerant bacterium enumerated from muddy soil was identified as Streptomyces tritici D5 through 16S rRNA sequencing. The identified S. tritici D5 strains showed excellent resistant and degradation potential at 100 mM concentration of potassium cyanide. Furthermore, the physicochemical properties analysis of sago industry effluents results revealed that the most of the parameters were crossing the permissible limits of Pollution control board of India. The bioremediation process was performed at various temperatures at 25 °C, 35 °C, and 45 °C for a period of 30 days of continuous bioremediation process with the aid of an aerator. Surprisingly, the best organic pollutant reduction was found at 35 °C and 45 °C, with 25 °C following close behind. Remarkably, the dissolved oxygen (DO) level was gradually increased from 2.24 to 12.04 mg L^-1 at 35 °C in 30 days of the remediation process. The pH and ammonia were also significantly increased during the bioremediation process in 30 days of treatment. Similarly, at 35 °C of bioremediation process the S. tritici D5 yielded maximum dried biomass (6.9 g L^-1) with the total crude protein (SCP) as 4.8 g L^-1 (69.56%) in 30 days of growth. These findings stated that S. tritici D5 can treat sago industry effluents and that the biomass produced may be considered SCP after some in-vitro and in-vivo analyses.

Fungi fabrication, characterization, and anticancer activity of silver nanoparticles using metals resistant Aspergillus niger

The purpose of this study was to assess the bio-fabrication possibilities of pre-isolated (from bauxite mine tailings) metal-tolerant Aspergillus niger biomass filtrate and the anticancer potential of synthesized silver nanoparticles (AgNPs) tested with a Human Cervical cancer cell line (HeLa cells: Henrietta Lacks cells). The nitrate reduction test demonstrated that A. niger has the ability to reduce nitrate, and filtrate derived from A. niger biomass efficiently fabricated AgNPs from AgNO₃, as demonstrated by a visible color change from pale greenish to brownish. The UV-visible spectroscopy analysis revealed an absorbance peak at 435 nm, which corresponded to the AgNPs. These AgNPs have been capped and stabilized with several functional groups related to various bioactive molecules such as aldehyde, benzene rings, aldehydic, amines, alcohols, and carbonyl stretch protein molecules. Fourier-Transform Infrared Spectroscopy (FTIR) analysis confirmed the capping and stabilizing chemical bonding pattern. Scanning Electron Microscopy (SEM) revealed that the synthesized AgNPs were spherical, with an average size of 21.38 nm. This bio-fabricated AgNPs has in-vitro anticancer potential when tested against the HeLa cell line due to its potential size and shape. At 100 g mL^-1 concentrations of this bio-fabricated AgNPs, the anticancer activity percentage was found to be 70.2%, and the IC₅₀ value was found to be 66.32 g m^-1. These findings demonstrated that the metal-tolerant A. niger cell filtrate could produce AgNPs with anticancer potential.

Silver nanoparticles (AgNPs) fabricating potential of aqueous shoot extract of Aristolochia bracteolata and assessed their antioxidant efficiency

This research was performed to evaluate the silver nanoparticles (AgNPs) fabricating potential of aqueous shoot extract of Aristolochia bracteolata and also assess the free radicals scavenging potential of synthesized AgNPs. The results obtained from this study showed that the aqueous shoot extract of A. bracteolata has the potential to synthesize the AgNPs and it was initially confirmed by color change in the reaction blend as yellow to dark brownish. Subsequently, a clear absorbance peak was found at 425 nm in UV-visible spectrum analysis. The functional groups involved in the capping and stabilization of AgNPs were confirmed by Fourier Transform-Infrared spectroscopy (FTIR) analysis and recorded about 10 sharp peaks 3688, 3401, 2980, 2370, 1948, 1642, 1480, 1280, 782, and 628 cm^-1. The Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM) observations revealed that the predominant shape of the AgNPs was spherical and size ranged from 41.43 to 60.51 nm. Interestingly, the green fabricated AgNPs showed significant free radicals scavenging activity and were confirmed with ferric reducing assay, 1, 1-diphenyl-2-picryl-hydrazyl (DPPH), H₂O₂ radicals, and 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radicals scavenging activity. Thus, after a few in-vivo antioxidant studies, Aristolochia bracteolata-mediated AgNPs can be considered as an antioxidant agent.