This Article Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Copyright Information Books from ASM Press MicrobeWorld Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Bringhurst, R. M. Articles by Gage, D. J. Search for Related Content PubMed PubMed Citation Articles by Bringhurst, R. M. Articles by Gage, D. J.

Control of Inducer Accumulation Plays a Key Role in Succinate-Mediated Catabolite Repression in Sinorhizobium meliloti

Department of Molecular and Cell Biology, University of Connecticut, Storrs, Connecticut 06269

Received 18 March 2002/ Accepted 24 June 2002

The symbiotic, nitrogen-fixing bacterium Sinorhizobium meliloti favors succinate and related dicarboxylic acids as carbon sources. As a preferred carbon source, succinate can exert catabolite repression upon genes needed for the utilization of many secondary carbon sources, including the -galactosides raffinose and stachyose. We isolated lacR mutants in a genetic screen designed to find S. meliloti mutants that had abnormal succinate-mediated catabolite repression of the melA-agp genes, which are required for the utilization of raffinose and other -galactosides. The loss of catabolite repression in lacR mutants was seen in cells grown in minimal medium containing succinate and raffinose and grown in succinate and lactose. For succinate and lactose, the loss of catabolite repression could be attributed to the constitutive expression of ß-galactoside utilization genes in lacR mutants. However, the inactivation of lacR did not cause the constitutive expression of -galactoside utilization genes but caused the aberrant expression of these genes only when succinate was present. To explain the loss of diauxie in succinate and raffinose, we propose a model in which lacR mutants overproduce ß-galactoside transporters, thereby overwhelming the inducer exclusion mechanisms of succinate-mediated catabolite repression. Thus, some raffinose could be transported by the overproduced ß-galactoside transporters and cause the induction of -galactoside utilization genes in the presence of both succinate and raffinose. This model is supported by the restoration of diauxie in a lacF lacR double mutant (lacF encodes a ß-galactoside transport protein) grown in medium containing succinate and raffinose. Biochemical support for the idea that succinate-mediated repression operates by preventing inducer accumulation also comes from uptake assays, which showed that cells grown in raffinose and exposed to succinate have a decreased rate of raffinose transport compared to control cells not exposed to succinate.

This article has been cited by other articles:

• Pinedo, C. A., Bringhurst, R. M., Gage, D. J. (2008). Sinorhizobium meliloti Mutants Lacking Phosphotransferase System Enzyme HPr or EIIA Are Altered in Diverse Processes, Including Carbon Metabolism, Cobalt Requirements, and Succinoglycan Production. J. Bacteriol. 190: 2947-2956 [Abstract] [Full Text]  
• Poysti, N. J., Loewen, E. D. M., Wang, Z., Oresnik, I. J. (2007). Sinorhizobium meliloti pSymB carries genes necessary for arabinose transport and catabolism. Microbiology 153: 727-736 [Abstract] [Full Text]  
• Deutscher, J., Francke, C., Postma, P. W. (2006). How Phosphotransferase System-Related Protein Phosphorylation Regulates Carbohydrate Metabolism in Bacteria. Microbiol. Mol. Biol. Rev. 70: 939-1031 [Abstract] [Full Text]