Characterization of the β-Ketoadipate Pathway inSinorhizobium meliloti Journal Articles uri icon

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abstract

  • ABSTRACTAromatic compounds represent an important source of energy for soil-dwelling organisms. The β-ketoadipate pathway is a key metabolic pathway involved in the catabolism of the aromatic compounds protocatechuate and catechol, and here we show through enzymatic analysis and mutant analysis that genes required for growth and catabolism of protocatechuate in the soil-dwelling bacteriumSinorhizobium melilotiare organized on the pSymB megaplasmid in two transcriptional units designatedpcaDCHGBandpcaIJF. ThepcaDpromoter was mapped by primer extension, and expression from this promoter is demonstrated to be regulated by the LysR-type protein PcaQ. β-Ketoadipate succinyl-coenzyme A (CoA) transferase activity inS. melilotiwas shown to be encoded by SMb20587 and SMb20588, and these genes have been renamedpcaIandpcaJ, respectively. These genes are organized in an operon with a putative β-ketoadipyl-CoA thiolase gene (pcaF), and expression of thepcaIJFoperon is shown to be regulated by an IclR-type transcriptional regulator, SMb20586, which we have namedpcaR. We show thatpcaRtranscription is negatively autoregulated and that PcaR is a positive regulator ofpcaIJFexpression and is required for growth ofS. melilotion protocatechuate as the carbon source. The characterization of the protocatechuate catabolic pathway inS. melilotioffers an opportunity for comparison with related species, includingAgrobacterium tumefaciens. Differences observed betweenS. melilotiandA. tumefaciens pcaIJoffer the first evidence ofpcagenes that may have been acquired after speciation in these closely related species.

publication date

  • August 2006