The Effects of Silver Nanoparticles (AgNPs) on Thermophilic Bacteria: Antibacterial, Morphological, Physiological and Biochemical Investigations.

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 2Cx, 3CA, 3CA1, FMB1, and 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. The growth inhibition curves showed that the 2Cx, and FMB2-1 strains were more sensitive to AgNPs, demonstrating a reduction in population by 71.1% and 31.7% at 62.5 μg mL and by 82.9% and 72.8% at 250 μg mL, 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; O) production. β-galactosidase biosynthesis decreased to 28.8% level at 500 μg mL AgNPs for 2Cx, 32.2% at 250 μg mL for FMB1, and 38.8% only at 62.5 μg mL, but it was completely inhibited at 500 μg mL for 3CA. Moreover, FMB2-1 showed a significant decrease to 11.2% at 125 μg mL. This study is the first to reveal the toxic effects of AgNPs on thermophilic bacteria.