Cadmium accumulation by immobilized cells of a Citrobacter sp. using various phosphate donors

Immobilized cells of a Citrobacter species scavenge cadmium with high efficiency from challenge flows containing Cd(2+). Metal uptake by the cells in mediated by a cellbound phosphatase which liberates inorganic phosphate from an organic phosphate to precipitate cadmium as cell-bound metal phosphate. Hitherto glycerol 2-phosphate has served as the phosphate donor, but for an economic large scale process an inexpensive and readily available phosphate donor is required and the use of alkyl phosphates was investigated. This was limited due to interference by the alcohol simultaneously liberated. An alternative, pulsed process is described whereby alkyl phosphate-supplemented main pulses interspersed with short alkyl phosphate-free "recovery" pulses greatly reduced the requirement for glycerol 2-phosphate. Wider aspects of phosphate donor utilization were also investigated to compare this strain of Citrobacter with a strain previously reported to accumulate lead but not cadmium.