Since thermophilic microorganisms are valuable sources of thermostable enzymes, it is essential to recognize the potential toxicity of silver nanoparticles used in diverse industrial sectors. Thermophilic bacteria Geobacillus vulcani 2Cx, Bacillus licheniformis 3CA, Paenibacillus macerans 3CA1, Anoxybacillus ayderensis FMB1, and Bacillus paralicheniformis FMB2-1 were selected, and their MIC and MBC values were assessed by treatment with AgNPs in a range of 62.5–1500 μg mL⁻¹. The growth inhibition curves showed that the G. vulcani 2Cx, and B. paralicheniformis FMB2-1 strains were more sensitive to AgNPs, demonstrating a reduction in population by 71.1% and 31.7% at 62.5 μg mL⁻¹ and by 82.9% and 72.8% at 250 μg mL⁻¹, respectively. TEM and FT-IR analysis revealed that AgNPs caused structural damage, cytoplasmic leakage, and disruption of cellular integrity. Furthermore, cell viability showed a significant decrease alongside an increase in superoxide radical (SOR; O₂⁻) production. β-galactosidase biosynthesis decreased to 28.8% level at 500 μg mL⁻¹ AgNPs for G. vulcani 2Cx, 32.2% at 250 μg mL⁻¹ for A. ayderensis FMB1, and 38.8% only at 62.5 μg mL⁻¹, but it was completely inhibited at 500 μg mL⁻¹ for B. licheniformis 3CA. Moreover, B. paralicheniformis FMB2-1 showed a significant decrease to 11.2% at 125 μg mL⁻¹. This study is the first to reveal the toxic effects of AgNPs on thermophilic bacteria.

The thermophilic amylase producing Anoxybacillus ayderensis FMB1 was isolated from Sorgun Hot Spring in Turkey. In order to obtain improved production of the enzyme for cost-effective process, optimization of the process parameters is required. Optimum conditions for amylase production were determined using the traditional Submerged Fermentation (SmF) method. The maximum amylase activity was 295.8 U/mg, under the optimized conditions (24-h, 55 °C, and pH 8.0) in liquid BMB medium. The best enzyme production was obtained in the presence of 1.5% soluble starch as carbon source and 1% yeast extract as nitrogen source. Enzyme was produced under optimal conditions and partially purified. Partially purified enzyme was stable for up to 120 minutes at 50 °C, and its stability was found to be pH 5.0–10.0. Regarding the effects of some metals and chemicals on the activity of the partially purified enzyme, Ca²⁺ increased the activity by 21%, but enzyme activity was decreased by Mg²⁺, Zn²⁺, Ni²⁺, and Cu²⁺ by 5%, 29%, 57%, and 64%, respectively. and the enzyme activity was completely inhibited by Hg²⁺. In addition; DTT, PMSF, PCMB, SDS and EDTA caused a decrease in enzyme activity by 3%, 4%, 12%, 27% and 77%, respectively. The molecular weight of enzyme was found to be 58.5 kDa by SDS-PAGE. The results obtained show that the thermophilic A. ayderensis FMB1 and their enzyme have biotechnological importance. Graphical Abstract