RESUMEN
C4-dicarboxylates and the C4-dicarboxylic amino acid l-aspartate support aerobic and anaerobic growth of Escherichia coli and related bacteria. In aerobic growth, succinate, fumarate, D- and L-malate, L-aspartate, and L-tartrate are metabolized by the citric acid cycle and associated reactions. Because of the interruption of the citric acid cycle under anaerobic conditions, anaerobic metabolism of C4-dicarboxylates depends on fumarate reduction to succinate (fumarate respiration). In some related bacteria (e.g., Klebsiella), utilization of C4-dicarboxylates, such as tartrate, is independent of fumarate respiration and uses a Na+-dependent membrane-bound oxaloacetate decarboxylase. Uptake of the C4-dicarboxylates into the bacteria (and anaerobic export of succinate) is achieved under aerobic and anaerobic conditions by different sets of secondary transporters. Expression of the genes for C4-dicarboxylate metabolism is induced in the presence of external C4-dicarboxylates by the membrane-bound DcuS-DcuR two-component system. Noncommon C4-dicarboxylates like l-tartrate or D-malate are perceived by cytoplasmic one-component sensors/transcriptional regulators. This article describes the pathways of aerobic and anaerobic C4-dicarboxylate metabolism and their regulation. The citric acid cycle, fumarate respiration, and fumarate reductase are covered in other articles and discussed here only in the context of C4-dicarboxylate metabolism. Recent aspects of C4-dicarboxylate metabolism like transport, sensing, and regulation will be treated in more detail. This article is an updated version of an article published in 2004 in EcoSal Plus. The update includes new literature, but, in particular, the sections on the metabolism of noncommon C4-dicarboxylates and their regulation, on the DcuS-DcuR regulatory system, and on succinate production by engineered E. coli are largely revised or new.
Asunto(s)
Transportadores de Ácidos Dicarboxílicos/metabolismo , Ácidos Dicarboxílicos/metabolismo , Proteínas de Escherichia coli/genética , Escherichia coli/crecimiento & desarrollo , Escherichia coli/metabolismo , Aerobiosis , Anaerobiosis , Transporte Biológico , Carboxiliasas/metabolismo , Ciclo del Ácido Cítrico , Transportadores de Ácidos Dicarboxílicos/genética , Escherichia coli/genética , Proteínas de Escherichia coli/metabolismo , Fumaratos/metabolismo , Regulación Bacteriana de la Expresión Génica , Humanos , Klebsiella/metabolismo , Proteínas de Transporte de Membrana/metabolismo , Ácido Succínico/metabolismoRESUMEN
DcuB of Escherichia coli catalyzes C4-dicarboxylate/succinate antiport during growth by fumarate respiration. The expression of genes of fumarate respiration, including the genes for DcuB (dcuB) and fumarate reductase (frdABCD) is transcriptionally activated by C4-dicarboxylates via the DcuS-DcuR two-component system, comprising the sensor kinase DcuS, which contains a periplasmic sensing domain for C4-dicarboxylates. Deletion or inactivation of dcuB caused constitutive expression of DcuS-regulated genes in the absence of C4-dicarboxylates. The effect was specific for DcuB and not observed after inactivation of the homologous DcuA or the more distantly related DcuC transporter. Random and site-directed mutation identified three point mutations (T394I, D398N, and K353A) in DcuB that caused a similar derepression as dcuB deletion, whereas the transport activity of the DcuB mutants was retained. Constitutive expression in the dcuB mutants depended on the presence of a functional DcuS-DcuR two-component system. Mutation of residues E79A, R83A, and R127A of DcuB, on the other hand, inactivated growth by fumarate respiration and transport of [14C]succinate, whereas the expression of dcuB'-'lacZ was not affected. Therefore, the antiporter DcuB is a bifunctional protein and has a regulatory function that is independent from transport, and sites for transport and regulation can be differentiated.
Asunto(s)
Antiportadores/genética , Transportadores de Ácidos Dicarboxílicos/metabolismo , Proteínas de Escherichia coli/metabolismo , Escherichia coli/metabolismo , Regulación Bacteriana de la Expresión Génica/fisiología , Mapeo Peptídico , Proteínas Quinasas/metabolismo , Sustitución de Aminoácidos , Antiportadores/metabolismo , Proteínas de Unión al ADN/genética , Proteínas de Unión al ADN/metabolismo , Transportadores de Ácidos Dicarboxílicos/genética , Escherichia coli/genética , Proteínas de Escherichia coli/genética , Fumaratos/metabolismo , Técnicas de Silenciamiento del Gen , Transporte Iónico/fisiología , Mutagénesis Sitio-Dirigida , Proteínas Quinasas/genética , Succinato Deshidrogenasa/genética , Succinato Deshidrogenasa/metabolismo , Succinatos/metabolismo , Factores de Transcripción/genética , Factores de Transcripción/metabolismoRESUMEN
Type 1 fimbriae of Escherichia coli facilitate attachment to the host mucosa and promote biofilm formation on abiotic surfaces. The transcriptional regulator LrhA, which is known as a repressor of flagellar, motility and chemotaxis genes, regulates biofilm formation and expression of type 1 fimbriae. Whole-genome expression profiling revealed that inactivation of lrhA results in an increased expression of structural components of type 1 fimbriae. In vitro, LrhA bound to the promoter regions of the two fim recombinases (FimB and FimE) that catalyse the inversion of the fimA promoter, and to the invertible element itself. Translational lacZ fusions with these genes and quantification of fimE transcript levels by real-time PCR showed that LrhA influences type 1 fimbrial phase variation, primarily via activation of FimE, which is required for the ON-to-OFF transition of the fim switch. Enhanced type 1 fimbrial expression as a result of lrhA disruption was confirmed by mannose-sensitive agglutination of yeast cells. Biofilm formation was stimulated by lrhA inactivation and completely suppressed upon LrhA overproduction. The effects of LrhA on biofilm formation were exerted via the changed levels of surface molecules, most probably both flagella and type 1 fimbriae. Together, the data show a role for LrhA as a repressor of type 1 fimbrial expression, and thus as a regulator of the initial stages of biofilm development and, presumably, bacterial adherence to epithelial host cells also.
Asunto(s)
Biopelículas/crecimiento & desarrollo , Proteínas de Escherichia coli/metabolismo , Escherichia coli/metabolismo , Fimbrias Bacterianas/metabolismo , Regulación Bacteriana de la Expresión Génica , Factores de Transcripción/metabolismo , Animales , Adhesión Bacteriana , Escherichia coli/genética , Escherichia coli/crecimiento & desarrollo , Escherichia coli/patogenicidad , Infecciones por Escherichia coli/microbiología , Infecciones por Escherichia coli/mortalidad , Proteínas de Escherichia coli/genética , Perfilación de la Expresión Génica , Humanos , Ratones , Mutación , Análisis de Secuencia por Matrices de Oligonucleótidos , Regiones Promotoras Genéticas , Factores de Transcripción/genética , Infecciones Urinarias/microbiología , Infecciones Urinarias/mortalidadAsunto(s)
ADN Bacteriano/química , Escherichia coli/metabolismo , Proteínas Mitocondriales/metabolismo , Regiones Promotoras Genéticas/genética , Cartilla de ADN , ADN Bacteriano/genética , Procesamiento de Imagen Asistido por Computador , Proteínas de la Membrana , Microscopía de Fuerza Atómica , Proteínas Mitocondriales/biosíntesis , Proteínas Mitocondriales/aislamiento & purificación , Unión Proteica , Reacción en Cadena de la Polimerasa de Transcriptasa InversaRESUMEN
C4-dicarboxylates, like succinate, fumarate, L- and D-malate, tartrate, and the C4-dicarboxylic amino acid aspartate, support aerobic and anaerobic growth of Escherichia coli and related bacteria and can serve as carbon and energy sources. In aerobic growth, the C4-dicarboxylates are oxidized in the citric acid cycle. Due to the interruption of the citric acid cycle under anaerobic conditions, anaerobic metabolism of the C4-dicarboxylates depends on fumarate reduction to succinate. In some related bacteria (e.g., Klebsiella), degradation of C4-dicarboxylates, like tartrate, uses a different mechanism and pathway. It requires the functioning of an Na+-dependent and membrane-associated oxaloacetate decarboxylase. Due to the incomplete function of the citric acid cycle in anaerobic growth, succinate supports only aerobic growth of E. coli. This chapter describes the pathways of and differences in aerobic and anaerobic C4-dicarboxylate metabolism and the physiological consequences. The citric acid cycle, fumarate respiration, and fumarate reductase are discussed here only in the context of aerobic and anaerobic C4-dicarboxylate metabolism. Some recent aspects of C4-dicarboxylate metabolism, such as transport and sensing of C4-dicarboxylates, and their relationships are treated in more detail.