The samples for ICP-OES were prepared following the protocols described in literatures.41 ,42 (link)
S. aureus RN4220 strains were cultured at 30 °C in 20 mL of CDM (supplemented with 0.5 μM CoCl2). When the cells grew to exponential phase (OD600 ∼ 0.6–0.8), the cultures were chilled on ice for 10 min and then harvested by centrifugation at 7000 g at 4 °C for 10 min. Pellets were washed 3 times using 1 mL of 2 mM EDTA solution, followed by a final wash with 1 mL MilliQ H2O. Next, cells were dried at 100 °C and then digested by 300 μL nitric acid (66–68% HNO3) for 12 h at 80 °C. After diluted to final volumns of 3 mL using MilliQ H2O, the samples were used for element measurements by using the inductively coupled plasma-optical emission spectrometry (iCAP 7000 Plus Series, Thermo Scientific™). Concentrations of cobalt ions of each sample were determined by standard solutions and was calculated assuming 4 × 108 cfu for an OD600 of 1 unit. Each experiment was repeated three times.
S. aureus RN4220 strains were cultured at 30 °C in 20 mL of CDM (supplemented with 0.5 μM CoCl2). When the cells grew to exponential phase (OD600 ∼ 0.6–0.8), the cultures were chilled on ice for 10 min and then harvested by centrifugation at 7000 g at 4 °C for 10 min. Pellets were washed 3 times using 1 mL of 2 mM EDTA solution, followed by a final wash with 1 mL MilliQ H2O. Next, cells were dried at 100 °C and then digested by 300 μL nitric acid (66–68% HNO3) for 12 h at 80 °C. After diluted to final volumns of 3 mL using MilliQ H2O, the samples were used for element measurements by using the inductively coupled plasma-optical emission spectrometry (iCAP 7000 Plus Series, Thermo Scientific™). Concentrations of cobalt ions of each sample were determined by standard solutions and was calculated assuming 4 × 108 cfu for an OD600 of 1 unit. Each experiment was repeated three times.