Media samples (1.0 mL) were boiled in 2.0 mL metal-free plastic centrifuge tubes (Eppendorf). Dried sample from 1 mL of media (MRS or CDM) was digested with 280 μL Milli-Q water and 15 μL trace metal concentrated nitric acid at 80°C for at least 12 h. Digested samples from a total of 8 mL media were diluted with 2% trace metal HNO3 to bring to a total volume of 3 mL. Sample was stored at 4°C until analysis by ICP-OES.
Medium samples were analyzed by an Agilent Simultaneous 725 ICP-OES equipped with VistaChip II CCD detector and image mapping technology (I-MAP) to provide complete wavelength coverage from 167 to 785 nm. Trace metal HNO3 (2%) was used as blank. Metal concentrations in media were measured by ICP-OES for Ca, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Se, Mo, and Cd. ICP-OES calibration standards contain 5,000, 2,000, 1,000, 750, 500, 250, 100, 40, 25, 16, 10, 5, 2.5, 1, and 0.5 ppb for each metal and were all prepared by diluting commercially available Inorganic Ventures' ICP-MS Complete Standard 71A (10 ppm) and Inorganic Ventures' ICP-MS Refractory Elements Standard 71B (10 ppm) with 2% trace metal HNO3.
Medium samples were analyzed by an Agilent Simultaneous 725 ICP-OES equipped with VistaChip II CCD detector and image mapping technology (I-MAP) to provide complete wavelength coverage from 167 to 785 nm. Trace metal HNO3 (2%) was used as blank. Metal concentrations in media were measured by ICP-OES for Ca, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Se, Mo, and Cd. ICP-OES calibration standards contain 5,000, 2,000, 1,000, 750, 500, 250, 100, 40, 25, 16, 10, 5, 2.5, 1, and 0.5 ppb for each metal and were all prepared by diluting commercially available Inorganic Ventures' ICP-MS Complete Standard 71A (10 ppm) and Inorganic Ventures' ICP-MS Refractory Elements Standard 71B (10 ppm) with 2% trace metal HNO3.