Cloning and transcriptional analysis of the Thermoanaerobacter ethanolicus strain 39E maltose ABC transport system

Abstract

Thermoanaerobacter ethanolicus strain 39E is a Gram-positive thermophile that converts sugars resulting from plant carbohydrate polymer degradation into ethanol. A putative maltose ATP-binding cassette (ABC) transport operon was isolated with genes encoding for the integral membrane components (malF and malG); the ATP-binding protein (malK); and a partial gene for the maltose-binding protein (malE). This operon is unlike most other maltose transport operons, which do not contain a contiguous malK gene. Sequence analysis showed that the individual genes in the putative operon possessed a considerable range of similarities to their respective homologs in other eubacteria and archaea. MalK had 52% amino-acid identity and over 70% similarity with its homolog from the archaeon Thermococcus litoralis, while the membrane components and binding protein exhibited much less similarity with a range of other thermophilic eubacteria. Transcript was not detected in maltose-, glucose-, or xylose-grown cells using Northern blotting, but RT-PCR showed that malFGK were expressed in cells grown on maltose or xylose. Based on these results, the strain 39E maltose operon may be subject to glucose catabolite repression.