Extracellular biosynthesis of silver nanoparticles (AgNPs) was explored using Thiosphaera pantotropha since this strain exhibits both nitrate- and nitrite-reductase enzyme activity (NaR and NiR, respectively). Optimal AgNP synthesis was achieved using 2 mM AgNO3, culture supernatant of nutrient broth grown T. pantotropha, and incubation at 37 °C and 180 rpm. Under these conditions, the localized surface plasmon resonance peak of silver at 404 nm matched well with the average size of the spherical AgNPs based on FEG-TEM micrographs, i.e., 14.6 nm (range: 5-51 nm). The zeta potential of -33.6 mV indicated good stability of the biosynthesized nanoparticles. The XRD spectra demonstrated the simultaneous presence of face-centered cubic crystal structure of AgNPs and AgCl NPs. Ag+ ions were possibly reduced by the NaR and NiR enzymes released into the culture media. The FTIR spectra confirmed the stabilization of the AgNPs by biomolecules present in the culture supernatant of T. pantotropha. The synthesized Ag/AgCl NPs exhibited good antibacterial efficacy against both Gram-negative (Escherichia coli and Pseudomonas aeruginosa) and Gram-positive bacteria (Bacillus subtilis and Staphylococcus aureus). The minimum inhibitory concentration (MIC) was 2.5 µg/ml for all the bacteria except B. subtilis (MIC of 10 µg/ml). The minimum bactericidal concentration (MBC) was 2.5, 10, 20, and 5 µg/ml for E. coli, P. aeruginosa, B. subtilis, and S. aureus, respectively. At MBC and higher AgNP concentration, both plating and CLSM imaging confirmed the absence of viable bacteria in treated water. The biogenic AgNPs depicted IC50 of 34.8 µg/ml for MCF-7 cells.

中文翻译：

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泛硫硫杆菌（Thiosphaera pantotropha）胞外合成银纳米颗粒及其抗菌和细胞毒性作用的评估。

由于该菌株同时具有硝酸盐还原酶和亚硝酸盐还原酶活性（分别为NaR和NiR），因此使用泛硫硫磷（Thiosphaera pantotropha）探索了银纳米颗粒（AgNPs）的细胞外生物合成。使用2 mM AgNO3，营养培养液培养的泛营养螺旋菌培养上清液，并在37°C和180 rpm下孵育，可获得最佳的AgNP合成。在这些条件下，基于FEG-TEM显微照片，银在404 nm处的局部表面等离振子共振峰与球形AgNP的平均尺寸非常匹配，即14.6 nm（范围：5-51 nm）。-33.6 mV的zeta电位表明生物合成的纳米颗粒具有良好的稳定性。XRD谱表明AgNPs和AgCl NPs的面心立方晶体结构同时存在。释放到培养基中的NaR和NiR酶可能会还原Ag +离子。FTIR光谱证实了存在于泛营养菌培养上清液中的生物分子对AgNP的稳定作用。合成的Ag / AgCl NPs对革兰氏阴性菌（大肠杆菌和铜绿假单胞菌）和革兰氏阳性菌（枯草芽孢杆菌和金黄色葡萄球菌）均显示出良好的抗菌效果。除枯草芽孢杆菌外，所有细菌的最低抑菌浓度（MIC）为2.5 µg / ml（MIC为10 µg / ml）。大肠杆菌，铜绿假单胞菌，枯草芽孢杆菌和金黄色葡萄球菌的最低杀菌浓度（MBC）分别为2.5、10、20和5 µg / ml。在MBC和更高的AgNP浓度下，平板和CLSM成像均证实处理过的水中不存在活菌。生物型AgNP的IC50为34。