Aerobic sulfide production and cadmium precipitation by Escherichia coli expressing the Treponema denticola cysteine desulfhydrase gene

The cysteine desulfhydrase gene of Treponema denticola was over-expressed i n Escherichia coli to produce sulfide under aerobic conditions and to preci pitate metal sulfide complexes on the cell wall. When grown in a defined sa lts medium supplemented with cadmium and cysteine, E. coli producing cystei ne desulfhydrase secreted sulfide and removed nearly all of the cadmium fro m solution after 48 h. A control strain produced significantly less sulfide and removed significantly less cadmium. Measurement of acid-labile sulfide and energy dispersive X-ray spectroscopy indicated that cadmium was precip itated as cadmium sulfide. Without supplemental cysteine, both the E. coli producing cysteine desulfhydrase and the control E. coli demonstrated minim al cadmium removal.