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 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.

Purification and Characterization of Thermostable and Detergent-Stable α-Amylase from Anoxybacillus sp. AH1

A thermostable and detergent-stable α-amylase from a newly isolated Anoxybacillus sp. AH1 was purified and characterized. Maximum enzyme production (1874.8 U/mL) was obtained at 24 h of incubation. The amylase was purified by using Sephadex G-75 gel filtration, after which an 18-fold increase in specific activity and a yield of 9% were achieved. The molecular mass of the purified enzyme was estimated at 85 kDa by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). The optimum pH and temperature values of the enzyme were 7.0 and 60 °C, respectively. The enzyme was highly stable in the presence of 30% glycerol, retaining 85% of its original activity at 60 °C within 120 min. Km and vmax values were 0.102 µmol and 0.929 µmol/min, respectively, using Lineweaver-Burk plot. The enzyme activity was increased by various detergents, but it was significantly inhibited in the presence of urea. Mg2+ and Ca2+ also significantly activated α-amylase, while Zn2+, Cu2+ and metal ion chelators ethylenediaminetetraacetic acid (EDTA) and 1,10-phenanthroline (phen) greatly inhibited the enzyme activity. α-Amylase activity was enhanced by β-mercaptoethanol (β-ME) and dithiothreitol (DTT) to a great extent, but inhibited by p-chloromercuribenzoic acid (PCMB). Iodoacetamide (IAA) and N-ethylmaleimide (NEM) had a slight, whereas phenylmethylsulfonyl fluoride (PMSF) had a strong inhibitory effect on the amylase activity.