Sd. Kelly et al., XAFS determination of the bacterial cell wall functional groups responsible for complexation of Cd and U as a function of pH, J SYNCHROTR, 8, 2001, pp. 946-948
Bacteria, which are ubiquitous in near-surface geologic systems, can affect
the distribution and fate of metals in these systems through adsorption re
actions between the metals and bacterial cell walls. Recently, Fein et al.
(1997) developed a chemical equilibrium approach to quantify metal adsorpti
on onto cell walls, treating the sorption as a surface complexation phenome
non. However, such models are based on circumstantial bulk adsorption evide
nce only, and the nature and mechanism of metal binding to cell walls for e
ach metal system have not been determined spectroscopically. The results of
XAFS measurements at the Cd K-edge and U L3-edge on Bacillus subtilis expo
sed to these elements show that, at low pH, U binds to phosphoryl groups wh
ile Cd binds to carboxyl functional groups.