A membrane bioreactor (MBR) was operated for the removal of methyl tert-butyl ether (MTBE) from water. Although the reactor was seeded with several cultures acclimated to MTBE degradation, a long start-up time was observed. Monitoring of the reactor with denaturing gradient gel electrophoresis (DGGE) revealed a dramatic shift in the MBR culture from the original seed culture, indicating that the membrane had exerted a selective pressure on the culture. The MBR culture was found to be dominated almost entirely by Sphingomonas, belonging to the a-4 subclass of the a-Proteobacteria. Several unique properties of Sphingomonas, including their characteristic outer membrane containing glycosphingolipids, as well as their extreme adeptness at xenobiotic degradation are hypothesized to have aided in their selection in this bioreactor.

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