This Article Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Copyright Information Books from ASM Press MicrobeWorld Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Hetzer, A. Articles by Morgan, H. W. Search for Related Content PubMed PubMed Citation Articles by Hetzer, A. Articles by Morgan, H. W. GeoRef GeoRef Citation Agricola Articles by Hetzer, A. Articles by Morgan, H. W.

Cadmium Ion Biosorption by the Thermophilic Bacteria Geobacillus stearothermophilus and G. thermocatenulatus

Thermophile Research Unit, University of Waikato, Te Whare Wananga o Waikato, Hamilton, New Zealand,¹ Institute of Geological and Nuclear Sciences, Lower Hutt, New Zealand²

Received 6 February 2006/ Accepted 30 March 2006

This study reports surface complexation models (SCMs) for quantifying metal ion adsorption by thermophilic microorganisms. In initial cadmium ion toxicity tests, members of the genus Geobacillus displayed the highest tolerance to CdCl₂ (as high as 400 to 3,200 µM). The thermophilic, gram-positive bacteria Geobacillus stearothermophilus and G. thermocatenulatus were selected for further electrophoretic mobility, potentiometric titration, and Cd²⁺ adsorption experiments to characterize Cd²⁺ complexation by functional groups within and on the cell wall. Distinct one-site SCMs described the extent of cadmium ion adsorption by both studied Geobacillus sp. strains over a range of pH values and metal/bacteria concentration ratios. The results indicate that a functional group with a deprotonation constant pK value of approximately 3.8 accounts for 66% and 80% of all titratable sites for G. thermocatenulatus and G. stearothermophilus, respectively, and is dominant in Cd²⁺ adsorption reactions. The results suggest a different type of functional group may be involved in cadmium biosorption for both thermophilic strains investigated here, compared to previous reports for mesophilic bacteria.