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Applied and Environmental Microbiology, June 2006, p. 4020-4027, Vol. 72, No. 6
0099-2240/06/$08.00+0     doi:10.1128/AEM.00295-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

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

Adrian Hetzer,1* Christopher J. Daughney,2 and Hugh W. Morgan1

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.

* Corresponding author. Mailing address: Thermophile Research Unit, University of Waikato, Te Whare Wananga o Waikato, Gate 1 Knighton Road, Private Bag 3105, Hamilton, New Zealand. Phone: (64) 7-838 4466-8265. Fax: (64) 7-838-4324. E-mail: hetzer.adrian{at}web.de.

Applied and Environmental Microbiology, June 2006, p. 4020-4027, Vol. 72, No. 6
0099-2240/06/$08.00+0     doi:10.1128/AEM.00295-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.





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