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J. Bacteriol. doi:10.1128/JB.01253-08
Copyright (c) 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Characterization of the myo-inositol utilization island of Salmonella enterica serovar Typhimurium

Zentralinstitut für Ernährungs- und Lebensmittelforschung (ZIEL), Abteilung Mikrobiologie, Technische Universität München, Weihenstephaner Berg 3, D-85354 Freising, Germany

^* To whom correspondence should be addressed. Email: thilo.fuchs{at}wzw.tum.de.

	Abstract

Knockout mutation of STM4432 resulted in a growth-deficient phenotype of Salmonella enterica serovar Typhimurium (S. Typhimurium) in the presence of myo-inositol (MI) as the sole carbon source. STM4432 is part of a 22.6 kb genomic island which spans from STM4417 to STM4436 (GEI 4417/4436) and is responsible for MI degradation. Genome comparison revealed the presence of this island in only six Salmonella strains, and a high variability of iol gene organization in Gram-negative bacteria. Upon non-polar deletion of eleven island loci, the genes involved in six enzymatic steps of the MI pathway were identified. The generation time of S. Typhimurium in minimal medium with MI decreases with higher concentrations of this polyol. RT-PCR showed five separate transcriptional units encompassing the genes iolA/iolB, iolE/iolG1, iolC1/iolC2, iolD1/iolD2/iolG2, and iolI2/iolH. Luciferase reporter assays revealed a strong induction of their promoters in the presence of MI, but not glucose. The main regulator, IolR, was identified due to a reduced lag-phase of a strain mutated in STM4417 (iolR). Deletion of iolR resulted in stimulation of the iol operons, indicating its negative effect on the iol genes of S. Typhimurium in rich medium at a transcriptional level. Bandshift assays demonstrated the binding of this putative repressor to promoter sequences of iolA, iolC1 and iolD1. Binding of IolR to its own promoter, and induced iolR expression in an IolR-negative background demonstrates that its transcription is autoregulated. Taken together, this is the first characterization of MI degradation in a Gram-negative bacterium, revealing a complex transcriptional organization and regulation of the S. Typhimurium iol genes.