Regulation of phenolic catabolism in Rhizobium leguminosarum biovar trifolii

Parke, Donna; Rynne, Fiona G.; Glenn, A. R.

doi:10.1128/jb.173.17.5546-5550.1991

Cited by 31 publications

(34 citation statements)

References 27 publications

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“…A study of pca gene regulation in R. leguminosarum bv. trifolii found that the transferase (PcaIJ) was induced by ␤-ketoadipate or its CoA derivative (39). In A. tumefaciens A348 as well, adipate, a nonmetabolizable analog of ␤-ketoadipate (36), induced PcaIJ, but not PcaB (Table 2).…”

Section: Resultsmentioning

confidence: 99%

“…Numerous genetic strategies have evolved to regulate the protocatechuate branch of the ␤-ketoadipate pathway in different microbes (24,38,39,48). Elucidation of the induction pattern in A. tumefaciens enables it to be compared with those of other species.…”

Section: Discussionmentioning

confidence: 99%

“…trifolii, the tricarboxylic acid ␤-carboxy-cis,cis-muconate induces at least two enzymes of the pathway, the decarboxylase and the hydrolase, while ␤-ketoadipate induces the transferase ( Fig. 1) (39). In A. tumefaciens, at least three genes for the hydrolase and the oxygenase are under the control of an activator that binds ␤-carboxy-cis,cis-muconate (34).…”

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Supraoperonic clustering of pca genes for catabolism of the phenolic compound protocatechuate in Agrobacterium tumefaciens

Parke

1995

J Bacteriol

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The protocatechuate branch of the ␤-ketoadipate pathway comprises the last six enzymatic steps in the catabolism of diverse phenolic compounds to citric acid cycle intermediates. In this paper, the regulation and tight supraoperonic clustering of the protocatechuate (pca) genes from Agrobacterium tumefaciens A348 are elucidated. A previous study found that the pcaD gene is controlled by an adjacent regulatory gene, pcaQ, which encodes an activator. The activator responded to ␤-carboxy-cis,cis-muconate and was shown to control the synthesis of at least three genes (pcaD and pcaHG). In this work, eight genes required for the catabolism of protocatechuate were localized within a 13.5-kb SalI region of DNA. Isolation and characterization of transposon Tn5 mutant strains facilitated the localization of pca genes. Five structural genes were found to respond to the tricarboxylic acid and to be contiguous in an operon transcribed in the order pcaDCHGB. These genes encode enzymes ␤-ketoadipate enol-lactone hydrolase, ␥-carboxymuconolactone decarboxylase, protocatechuate 3,4-dioxygenase (pcaHG), and ␤-carboxy-cis,cis-muconate lactonizing enzyme, respectively. Approximately 4 kb from the pcaD gene are the pcaIJ genes, which encode ␤-ketoadipate succinyl-coenzyme A transferase for the next-to-last step of the pathway. The pcaIJ genes are transcribed divergently from the pcaDCHGB operon and are expressed in response to ␤-ketoadipate. The pattern of induction of pca genes by ␤-carboxy-cis,cis-muconate and ␤-ketoadipate in A. tumefaciens is similar to that observed in Rhizobium leguminosarum bv. trifolii and is distinct from induction patterns for the genes from other microbial groups.Diverse aromatic compounds, arising in soil and water from origins in living plants, plant litter, or industrial processes, are degraded to common diphenolic intermediates, catechol and protocatechuate. Specific dioxygenases cleave these two phenolics, initiating the two branches of the ␤-ketoadipate pathway which funnel aromatic compounds into the tricarboxylic acid cycle (48). The ability of members of the bacterial family Rhizobiaceae to catabolize numerous aromatic compounds via the catechol or protocatechuate branch of the ␤-ketoadipate pathway has been documented (6,7,26,37,38). Remarkably, the protocatechuate branch of the pathway (Fig. 1) appears to be universally distributed among members of this highly diverse bacterial group (21, 37). Previous research has demonstrated the inducibility of enzymes of the ␤-ketoadipate pathway in fast-growing representatives of the family Rhizobiaceae and the constitutivity of most enzymes in slowly growing Bradyrhizobium species (38).As a multistep ensemble, peripheral to the heart of bacterial metabolism, the ␤-ketoadipate pathway provides a model system for studying the mechanisms of regulation and evolution of catabolic pathways. Its acquisition and maintenance in the face of different selection pressures might be expected to be mediated by diversification of gene organization and regulation. The reg...

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Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

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Supraoperonic clustering of pca genes for catabolism of the phenolic compound protocatechuate in Agrobacterium tumefaciens

Parke

1995

J Bacteriol

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“…The first step in the metabolism of these compounds involves their conversion into either protocatechuate or catechol, which is subsequently metabolized to tricarboxylic acid intermediates via the ␤-ketoadipate pathway (18). This metabolic pathway has been documented in many members of the family Rhizobiaceae (23,35,(38)(39)(40), suggesting that the ␤-ketoadipate pathway is important for the survival of these soil-dwelling microorganisms.Sinorhizobium meliloti is a gram-negative, soil-dwelling bacterium that participates in a symbiotic relationship with the legume alfalfa through the establishment of nitrogen-fixing root nodules. Enzymes involved in the protocatechuate branch of the ␤-ketoadipate pathway in S. meliloti are encoded within the pcaDCHGB and pcaIJF operons, which are subject to regulation by products encoded by pcaQ and pcaR, respectively (23).…”

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Binding Site Determinants for the LysR-Type Transcriptional Regulator PcaQ in the Legume Endosymbiont Sinorhizobium meliloti

2008

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LysR-type transcriptional regulators represent one of the largest groups of prokaryotic regulators described to date. In the gram-negative legume endosymbiont Sinorhizobium meliloti, enzymes involved in the protocatechuate branch of the ␤-ketoadipate pathway are encoded within the pcaDCHGB operon, which is subject to regulation by the LysR-type protein PcaQ. In this work, purified PcaQ was shown to bind strongly (equilibrium dissociation constant, 0.54 nM) to a region at positions ؊78 to ؊45 upstream of the pcaD transcriptional start site. Within this region, we defined a PcaQ binding site with dyad symmetry that is required for regulation of pcaD expression in vivo and for binding of PcaQ in vitro. We also demonstrated that PcaQ participates in negative autoregulation by monitoring expression of pcaQ via a transcriptional fusion to lacZ. Although pcaQ homologues are present in many ␣-proteobacteria, this work describes the first reported purification of this regulator, as well as characterization of its binding site, which is conserved in Agrobacterium tumefaciens, Rhizobium leguminosarum, Rhizobium etli, and Mesorhizobium loti.In a soil environment, plant-derived aromatic acids represent significant carbon and energy sources. The first step in the metabolism of these compounds involves their conversion into either protocatechuate or catechol, which is subsequently metabolized to tricarboxylic acid intermediates via the ␤-ketoadipate pathway (18). This metabolic pathway has been documented in many members of the family Rhizobiaceae (23,35,(38)(39)(40), suggesting that the ␤-ketoadipate pathway is important for the survival of these soil-dwelling microorganisms.Sinorhizobium meliloti is a gram-negative, soil-dwelling bacterium that participates in a symbiotic relationship with the legume alfalfa through the establishment of nitrogen-fixing root nodules. Enzymes involved in the protocatechuate branch of the ␤-ketoadipate pathway in S. meliloti are encoded within the pcaDCHGB and pcaIJF operons, which are subject to regulation by products encoded by pcaQ and pcaR, respectively (23). The regulator encoded by pcaQ is a member of the LysR-type transcriptional regulator (LTTR) superfamily, and PcaQ homologues are present in many species of ␣-proteobacteria (3,4,7,23,34,36,37).LysR-type regulators comprise one of the largest groups of prokaryotic transcriptional regulators characterized to date; these proteins regulate a diverse range of regulons, including genes whose products are involved in nitrogen and carbon fixation, biofilm formation, the oxidative stress response, bacterial virulence, and the catabolism of various compounds, including aromatic acids (10,16,19,22,23,28,34,46,47,51,55,57). LTTR proteins consist of a conserved helix-turn-helix DNA binding motif located in the N-terminal portion of the polypeptide, whereas the C terminus includes an inducer binding site. As a general rule, LTTRs act as transcriptional activators by inducing expression of a target gene(s) upon interaction with a coeffector molecule,...

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