Enhanced Antioxidant Activity of Nano-Selenium Produced Using a Bacterial Isolate Citrobacter sp.

Selenium is essential for human, plant, and animal growth and reproduction. Because of their biological activity, bioavailability, and low toxicity, selenium nanoparticles are regarded as a promising material for many applications in biomedicine and health. Selenium-resistant bacteria were isolated from garden soil and identified as Citrobacter amalonaticus strain ARB01. TEM, UV-visible spectrophotometer, FTIR, and EDAX were used to characterize biosynthesized SeNPs using the cell-free extract of ARB01. The antioxidant activity of biologically functionalized SeNPs was evaluated using the 1, 1-diphenyl-2-picrylhydrazyl (DPPH), ferric reducing antioxidant strength (FRAP), and 2, 2′-azinobis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) assays. The Dot-blot test was used to perform a qualitative study of the antioxidant activity of SeNPs using the TLC-DPPH technique. The TEM analysis revealed spherical SeNPs with diameters ranging from 50 nm to 80 nm. Because of the synergistic effect of biomolecules involved in nanoparticle synthesis, SeNPs showed higher antioxidant activity. This study reveals that the antioxidant activity of nanoparticles increased due to functionalization by biomolecules present in the cell-free extract of bacterial isolate.

Electron carriers involved in autotrophic and heterotrophic acetogenesis in the thermophilic bacterium Thermoanaerobacter kivui

Thermoanaerobacter kivui is an acetogenic model organism that reduces CO2 with electrons derived from H2 or CO, or from organic substrates in the Wood–Ljugdahl pathway (WLP). For the calculation of ATP yields, it is necessary to know the electron carriers involved in coupling of the oxidative and reductive parts of metabolism. Analyses of key catabolic oxidoreductases in cell-free extract (CFE) or with purified enzymes revealed the physiological electron carriers involved. The glyceraldehyde-3-phosphate dehydrogenase (GA3P-DH) assayed in CFE was NAD+-specific, NADP+ was used with less than 4% and ferredoxin (Fd) was not used. The methylene-THF dehydrogenase was NADP+-specific, NAD+ or Fd were not used. A Nfn-type transhydrogenase that catalyzes reduced Fd-dependent reduction of NADP+ with NADH as electron donor was also identified in CFE. The electron carriers used by the potential electron-bifurcating hydrogenase (HydABC) could not be unambiguously determined in CFE for technical reasons. Therefore, the enzyme was produced homologously in T. kivui and purified by affinity chromatography. HydABC contained 33.9 ± 4.5 mol Fe/mol of protein and FMN; it reduced NADP+ but not NAD+. The methylene-THF reductase (MetFV) was also produced homologously in T. kivui and purified by affinity chromatography. MetFV contained 7.2 ± 0.4 mol Fe/mol of protein and FMN; the complex did neither use NADPH nor NADH as reductant but only reduced Fd. In sum, these analysis allowed us to propose a scheme for entire electron flow and bioenergetics in T. kivui.

Molecular Umbrella as a Nanocarrier for Antifungals

A molecular umbrella composed of two O-sulfated cholic acid residues was applied for the construction of conjugates with cispentacin, containing a “trimethyl lock” (TML) or o-dithiobenzylcarbamoyl moiety as a cleavable linker. Three out of five conjugates demonstrated antifungal in vitro activity against C. albicans and C. glabrata but not against C. krusei, with MIC90 values in the 0.22–0.99 mM range and were not hemolytic. Antifungal activity of the most active conjugate 24c, containing the TML–pimelate linker, was comparable to that of intact cispentacin. A structural analogue of 24c, containing the Nap-NH2 fluorescent probe, was accumulated in Candida cells, and TML-containing conjugates were cleaved in cell-free extract of C. albicans cells. These results suggest that a molecular umbrella can be successfully applied as a nanocarrier for the construction of cleavable antifungal conjugates.