Tellurite (TeO₃²⁻) is a highly soluble and toxic oxyanion that inhibits the growth of Escherichia coli at concentrations as low as ~1 µg/mL. This toxicity has been primarily attributed to the generation of reactive oxygen species (ROS) during its intracellular reduction by thiol-containing molecules and NAD(P)H-dependent enzymes. However, under anaerobic conditions, E. coli exhibits significantly increased tellurite tolerance—up to 100-fold in minimal media—suggesting the involvement of additional, ROS-independent mechanisms. In this study, we combined chemical-genomic screening, untargeted metabolomics, and targeted biochemical assays to investigate the effects of tellurite under both aerobic and anaerobic conditions. Our findings reveal that tellurite perturbs amino acid and nucleotide metabolism, leading to intracellular imbalances that impair protein synthesis. Additionally, tellurite induces notable changes in membrane lipid composition, particularly in phosphatidylethanolamine derivatives, which may influence biophysical properties of the membrane, such as fluidity or curvature. This membrane remodeling could contribute to the increased resistance observed under anaerobic conditions, although direct evidence of altered membrane fluidity remains to be established. Overall, these results demonstrate that tellurite toxicity extends beyond oxidative stress, impacting central metabolic pathways and membrane-associated functions regardless of oxygen availability.

Bacteria in natural environments often encounter high concentrations of metal ions, leading to the development of defense mechanisms such as chemical reduction. This process can result in the formation of nanostructures (NS) ranging from 1–100 nm, which have valuable properties for various applications, including as virucidal agents. Currently, metallic NS with virucidal activity are used in disinfectants and surface protection products. However, their production mainly relies on physical and chemical methods, which are often complex, toxic, and energy-intensive. A sustainable alternative is the biosynthesis of nanostructures. Our research focuses on the biosynthesis of gold nanostructures (AuNS) using environmental bacteria and their proteins, with the aim of exploring their potential as agents to destroy the influenza A virus. We screened bacteria under conditions with HAuCl₄, identifying eight microorganisms capable of growing in high gold concentrations. Staphylococcus haemolyticus BNF01 showed the highest resistance and Au(III) reduction, growing up to 0.25 mM in HAuCl₄. Bioinformatic analysis revealed five proteins with potential Au(III)-reductase activity, which were cloned and expressed in Escherichia coli. These proteins reduced gold to form AuNPs, which were purified, characterized for size, shape, and surface charge, and tested against influenza A, showing significant virucidal effects, likely due to interactions with viral proteins.

D-tagatose is a high-value, low-calorie sweetener that can be produced from dairy lactose via a two-step enzymatic route: lactose hydrolysis to galactose followed by galactose isomerization to tagatose. Here, we combined genomics, in silico structural analysis, and biochemical assays to evaluate the lactose-to-tagatose conversion potential of an Antarctic isolate, L47, identified as Ewingella americana (NCBI accession SAMN54554459). Genome mining revealed one L-arabinose isomerase gene (araA) and three β-galactosidase genes (bgaA, bglY, lacZ), an uncommon combination in a single bacterium. Recombinant AraA was produced in Escherichia coli and biochemically characterized, showing Mn²⁺ dependence and measurable D-galactose isomerization, reaching ~18% tagatose from 100 mM galactose after 48 h under the tested conditions. In contrast, the β-galactosidases were predominantly recovered as insoluble aggregates in E. coli; therefore, β-galactosidase activity was assessed using washed inclusion-body preparations. Under these conditions, BgaA displayed the most consistent o-NPG hydrolyzing activity, whereas BglY and LacZ did not yield reproducible activity. Overall, our results identify BgaA as the most tractable lactose-hydrolyzing candidate from L47 in the current workflow and indicate that AraA performance is the principal bottleneck toward an efficient lactose-to-tagatose process, motivating future optimization at the enzyme and process levels.