Study of Copper Accumulation by the Type I Methanotroph Methylomicrobium albus BG8

Copper accumulation, which includes both sorption and uptake, has been investigated in the type I methanotroph Methylomicrobium albus BG8 at copper concentrations that were neither growth limiting nor toxic. The disappearance of the cupric ion [Cu^(2+)(H_2O)_6] from the growth medium was studied using a copper-selective electrode and was compared with total copper accumulation by the cells assayed by inductively coupled plasma/mass spectrometry. The amount of copper accumulated by the cells was related to the cupric ion concentration rather than to that of the total copper added to the growth medium. Copper accumulation demonstrated a hyperbolic dependence on cupric ion concentration, suggesting the saturation of copper binding sites on the cell surface. A mean maximum binding capacity was estimated as 1.54 × 10^(-15) mol/cell and an apparent half-saturation constant as 1.43 × 10^(-7) mol/L. Sorption experiments established that most of the copper accumulated by the cells was removable by EDTA. The portion of the copper in the cellular fraction that was not removed by EDTA showed a rapid saturation at 1−3 × 10^(-17) mol of copper/cell despite a 100-fold variation in medium total copper and cupric ion concentrations. The copper accumulated by the cells that was EDTA-removable was not available for either direct or indirect uptake by the cells.