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The Maltodextrin System of Escherichia coli: Glycogen-Derived Endogenous Induction and Osmoregulation

Renate Dippel, Tobias Bergmiller, Alex Böhm, and Winfried Boos^*

Department of Biology, University of Konstanz, 78457 Konstanz, Germany

Received 27 May 2005/ Accepted 23 August 2005

Strains of Escherichia coli lacking MalQ (maltodextrin glucanotransferase or amylomaltase) are endogenously induced for the maltose regulon by maltotriose that is derived from the degradation of glycogen (glycogen-dependent endogenous induction). A high level of induction was dependent on the presence of MalP, maltodextrin phosphorylase, while expression was counteracted by MalZ, maltodextrin glucosidase. Glycogen-derived endogenous induction was sensitive to high osmolarity. This osmodependence was caused by MalZ. malZ, the gene encoding this enzyme, was found to be induced by high osmolarity even in the absence of MalT, the central regulator of all mal genes. The osmodependent expression of malZ was neither RpoS nor OmpR dependent. In contrast, the malPQ operon, whose expression was also increased at a high osmolarity, was partially dependent on RpoS. In the absence of glycogen, residual endogenous induction of the mal genes that is sensitive to increasing osmolarity can still be observed. This glycogen-independent endogenous induction is not understood, and it is not affected by altering the expression of MalP, MalQ, and MalZ. In particular, its independence from MalZ suggests that the responsible inducer is not maltotriose.

Present address: Division of Molecular Microbiology, Biozentrum, University of Basel, Klingelbergstrasse 50/70, 4056 Basel, Switzerland.

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