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Appl Environ Microbiol. 1994 September; 60(9): 3079-3088
Copyright © 1994, American Society for Microbiology. All Rights Reserved.

Adsorption of Rhodococcus Strain GIN-1 (NCIMB 40340) on Titanium Dioxide and Coal Fly Ash Particles

¹ Program for Biotechnology, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel
² Department of Molecular Microbiology and Biotechnology, Tel-Aviv University, Ramat-Aviv 69978, Israel

ABSTRACT

Rhodococcus strain GIN-1 (NCIMB 40340) can be used to enrich and isolate a titanium-rich fraction from coal fly ash. The gram-positive bacterium was isolated by its ability to adhere strongly and rapidly to suspended particles of pure titanium dioxide or coal fly ash. Adsorption depends on the salt concentration and occurs in seawater. Lowering of the salt concentration or washing of particles with pure water did not, however, cause desorption of the bacteria from TiO₂ particles; this was achieved by strong alkaline treatment or combined treatment with sodium dodecyl sulfate and urea but not with dilute acids, alcohols, or cationic or nonionic detergents. The bacterium exhibits higher affinity towards oxides of Ti and Zn than to other oxides with similar distribution of particle size. Moreover, it adheres much faster to TiO₂ than to magnetite (Fe₃O₄) or Al₂O₃. After about 1 min, more than 85% of the cells were adsorbed on TiO₂, compared with adsorption of only 10 and 8% to magnetite and Al₂O₃, respectively. Adsorption of the bacteria on TiO₂ occurs over a pH range of 1.0 to 9.0 and at temperatures from 4 to over 80°C. Scanning electron microscopy combined with X-ray analysis revealed preferential adherence of the bacterium to coal ash particles richer in Ti. Stronger adhesion to TiO₂ was also demonstrated in the translocation of bacteria, preadsorbed on magnetite, to TiO₂ particles. The temporary co-adhesion to magnetite and TiO₂ was exploited for the design of a prototype biomagnetic separation process in which bacterial cells serve as an adhesive mediator between magnetite and TiO₂ particles in a mixture of Al, Si, and Ti oxides that simulates their proportion in the ash.

^* Corresponding author. Mailing address: Program for Biotechnology, Ben-Gurion University of the Negev, P.O. Box 653, Beer-Sheva 84105, Israel. Phone: 972-7-461799. Fax: 972-7-236446.

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