TC(VII) REDUCTION AND ACCUMULATION BY IMMOBILIZED CELLS OF ESCHERICHIA-COLI

Resting cells of Escherichia coli, immobilized in a flow-through biore actor, coupled the oxidation of formate or hydrogen to Tc(VII) reducti on and removal from solution. Cells, pregrown anaerobically in a hollo w-fiber membrane bioreactor, were challenged with 50 mu M Tc(VII) in a carrier solution of phosphate-buffered saline. The radionuclide accum ulated within the membrane component of the reactor, corresponding to the localization of the cells. Negligible Tc removal was noted in a re actor containing a mutant deficient in active Tc(VII) reductase, when supplied with formate as an electron donor. Formate or hydrogen was su pplied as the electron donor for Tc(VII) reduction to cells immobilize d in reactors operated in transverse (crossflow) and direct (dead-end filtration) modes, respectively. Flow-rate activity relationships were used to compare the performance of the reactors. A flow rate of 2.4 m Lh(-1) supported the removal of 50% of the Tc from solution in a react or operated in transverse mode with formate as an electron donor. In c ontrast, a flow rate of 0.7 mLh(-1), supported comparable Tc removal w hen hydrogen was introduced to a reactor operated in direct mode. The reduced reactor efficiency, when hydrogen was used as an electron dono r, could be attributed, in part, to poor delivery of the gas to the ce lls. The biocatalyst was highly stable in the reactor; no loss in acti vity was noted over 200 h of continuous use. (C) 1997 John Wiley & Son s, Inc.