Experimental studies were performed to evaluate
the high capacity of cadmium removal by
Desulfovibrio alaskensis
strain 6SR, which is a sulfate-reducing
bacterium. The study was conducted in batch cultures of
D. alaskensis 6SR in a medium with a high cadmium
concentration. The results indicated that bacterial growth
was not dramatically affected by the presence of 170 mg/L
of cadmium, following a similar behavior to that of the
control culture. Besides, we observed a fast production of
extracellular polymeric substances, which play an important
role in cadmium removal. The bacterium was able to
remove 99.9 % of cadmium at the tested concentration.
The main mechanism of cadmium removal was its precipitation
as cadmium sulfide (yellow precipitate), followed
by its adsorption in the polymeric substances. Most
cadmium up take occurred within the first 48 h, and the
largest cadmium adsorption capacity was achieved at
144 h. Cadmium adsorption dynamics was evaluated by
pseudo-first order and pseudo-second-order kinetic models;
where the best adjustment was obtained with the pseudosecond-
order model. The micrographs, obtained with
transmission electron microscopy, showed a very low
intracellular and periplasmic accumulation of cadmium in
the cells. Thereby, this bacterium facilitates a process of
removal and recovery of cadmium at high concentrations
without the need of cellular lysis or special washes.
