A strain of Mycobacterium austroafricanum capable of mineralizing methyl tert-butyl ether (MtBE) as its sole carbon and energy source had previously been isolated from activated sludge. The use of this bacteria in a biobarrier system for the in situ treatment of contaminated groundwater was the ultimate goal of this work. This paper reports the results of initial studies to find an appropriate immobilizing or support material. Several materials (peat, perlite, pozzolan, pumice and granulated activated carbon) were considered. Selection was based on the measurement and comparison of their abilities to immobilize or retain the bacteria, and to adsorb MtBE. The immobilization test was based on monitoring the respiration of bacteria remaining on the material after initial contact times of either 24 or 72 h. O-2 consumption and CO2 production were measured over a period of time. The study showed that perlite was the best material. Adsorption isotherms for MtBE were constructed for each support. The strength of adsorption coefficient, K-f, in the Freundlich equation was calculated and used as the basis for comparison of their adsorptive capacities. The strength of adsorption was highest for the granulated activated carbon, and the K-f values for the other materials were relatively low and fell within the same range. However, since GAC performed poorly in the immobilization test, perlite was selected as the best support material. (C) 2006 Elsevier Inc. All rights reserved.