METAL-BINDING PROPERTIES OF KLEBSIELLA-OXYTOCA

Bacterial surfaces are generally negatively charged in the environmental pH-range and may therefore interact with metal cations, thus influencing the mobility of metals in soil and natural waters. In the present work the acid capacity and metal binding properties of Klebsiella oxytoca have been studied. A total acid capacity of 120 meq kg-1 was determined from potentiometric titrations of a suspension of starved bacteria in 0.1 M KCl. The adsorption of trace elements (Cs, Sr, Eu, serving as model systems, as well as Hg, Zn, and As) on starved bacteria was determined by a batch technique using radio tracers and with variation of pH (3 to 9). The adsorption followed the order Cs < Sr, As < Zn < Hg < Eu (at pH 5 to 7). The uptake of Eu was drastically increased when pH increased from 3.5 to 4.5, indicating a surface complexation (with carboxylic or phosphate groups). A desorption of Eu at pH above the acid equivalence point (pH 6.9) could be an indication of the release of a metal complexing exudate from the bacteria.