Aer and Tsr guide Escherichia coli in spatial gradients of oxidizable substrates

Greer‐Phillips, Suzanne E.; Alexandre, Gladys; Taylor, Barry; Zhulin, Igor B.

doi:10.1099/mic.0.26304-0

Cited by 47 publications

(60 citation statements)

References 27 publications

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“…By using a variety of null mutants, it was established that the chemotrophic response towards PTS sugars was elicited by their transport and not by their binding or metabolism (8,297,462,641,948). It was established that chemotaxis towards PTS sugars at relatively high concentrations (Ͼ1 mM) is also mediated by the chemoreceptors Aer and Tsr (296), which sense redox state and proton motive force, respectively (865). In E. coli, chemotaxis by PTS sugars can be abolished by knocking out CheA, CheY, CheW, EI, HPr, or the corresponding sugar-specific EII complexes, whereas the removal of the MCPs, CheR, or CheB has no significant effect (8,297,460,462,498,550,609,641,745,863,864; see also reference 678).…”

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confidence: 99%

How Phosphotransferase System-Related Protein Phosphorylation Regulates Carbohydrate Metabolism in Bacteria

Deutscher

Francke

Postma

2006

Microbiol Mol Biol Rev

1,202

769

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SUMMARY The phosphoenolpyruvate(PEP):carbohydrate phosphotransferase system (PTS) is found only in bacteria, where it catalyzes the transport and phosphorylation of numerous monosaccharides, disaccharides, amino sugars, polyols, and other sugar derivatives. To carry out its catalytic function in sugar transport and phosphorylation, the PTS uses PEP as an energy source and phosphoryl donor. The phosphoryl group of PEP is usually transferred via four distinct proteins (domains) to the transported sugar bound to the respective membrane component(s) (EIIC and EIID) of the PTS. The organization of the PTS as a four-step phosphoryl transfer system, in which all P derivatives exhibit similar energy (phosphorylation occurs at histidyl or cysteyl residues), is surprising, as a single protein (or domain) coupling energy transfer and sugar phosphorylation would be sufficient for PTS function. A possible explanation for the complexity of the PTS was provided by the discovery that the PTS also carries out numerous regulatory functions. Depending on their phosphorylation state, the four proteins (domains) forming the PTS phosphorylation cascade (EI, HPr, EIIA, and EIIB) can phosphorylate or interact with numerous non-PTS proteins and thereby regulate their activity. In addition, in certain bacteria, one of the PTS components (HPr) is phosphorylated by ATP at a seryl residue, which increases the complexity of PTS-mediated regulation. In this review, we try to summarize the known protein phosphorylation-related regulatory functions of the PTS. As we shall see, the PTS regulation network not only controls carbohydrate uptake and metabolism but also interferes with the utilization of nitrogen and phosphorus and the virulence of certain pathogens.

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confidence: 99%

How Phosphotransferase System-Related Protein Phosphorylation Regulates Carbohydrate Metabolism in Bacteria

Deutscher

Francke

Postma

2006

Microbiol Mol Biol Rev

1,202

769

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“…This behavior in E. coli has been studied extensively (12,13,18,30,32) and has been described for other FIG. 4.…”

Section: Discussionmentioning

confidence: 99%

An Energy Taxis Transducer Promotes Root Colonization byAzospirillum brasilense

2004

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Motility responses triggered by changes in the electron transport system are collectively known as energy taxis. In Azospirillum brasilense, energy taxis was shown to be the principal form of locomotor control. In the present study, we have identified a novel chemoreceptor-like protein, named Tlp1, which serves as an energy taxis transducer. The Tlp1 protein is predicted to have an N-terminal periplasmic region and a cytoplasmic C-terminal signaling module homologous to those of other chemoreceptors. The predicted periplasmic region of Tlp1 comprises a conserved domain that is found in two types of microbial sensory receptors: chemotaxis transducers and histidine kinases. However, the function of this domain is currently unknown. We characterized the behavior of a tlp1 mutant by a series of spatial and temporal gradient assays. The tlp1 mutant is deficient in (i) chemotaxis to several rapidly oxidizable substrates, (ii) taxis to terminal electron acceptors (oxygen and nitrate), and (iii) redox taxis. Taken together, the data strongly suggest that Tlp1 mediates energy taxis in A. brasilense. Using qualitative and quantitative assays, we have also demonstrated that the tlp1 mutant is impaired in colonization of plant roots. This finding supports the hypothesis that energy taxis and therefore bacterial metabolism might be key factors in determining host specificity in Azospirillum-grass associations.Azospirillum brasilense, a free-living diazotroph that belongs to the alpha-subdivision of proteobacteria, associates with the roots of many agriculturally important crops, including wheat, corn, and rice. Azospirilla colonize the root surface and may significantly promote plant growth and crop yield, properties that make them attractive candidates for the development of biological fertilizers for these crops (26-28). The ability of Azospirillum to attain significant populations on the root surfaces of the host is essential for its beneficial effect on plant growth and requires that the bacteria come in close contact with the roots (9,27,28,35). The abilities of sensing chemicals released by the host plant and navigating toward the root system are likely to be important for the establishment of bacteria, including Azospirillum (9, 10, 42), in the rhizosphere. Experimental evidence supporting this hypothesis was obtained by demonstrating that nonchemotactic and nonmotile mutants of A. brasilense are severely impaired in surface colonization of wheat roots (41). Although there is no strict host specificity in Azospirillum-plant associations, a strain-specific chemotaxis was reported: strains isolated from the rhizosphere of a particular grass demonstrated preferential chemotaxis toward chemicals found in root exudates of that grass (31). These results suggested that chemotaxis may contribute to host-plant specificity and could largely be determined by metabolism (31).Most motility responses in A. brasilense are a particular form of metabolism-dependent taxis called energy taxis (1). In energy taxis, a flow of reducing equ...

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“…6). Similar Aer-Tsr chimeras have been reported (8,38), but we chose the Tar signaling domain to avoid potential complications of Tsr, which also plays a role in aerosensing behavior (23,37,57). The Aer and Tar proteins were joined at two homologous positions near the junction of their HAMP and signaling domains, creating chimeras with the PAS-HAMP portion of Aer and the signaling domain of Tar, including its methylation sites and C-terminal CheR/CheB tethering site (Fig.…”

Section: X-x-e-(e/q)-x-(a/t/s)-a-(a/s/t) (24 32 52mentioning

confidence: 99%

Methylation-Independent Aerotaxis Mediated by the Escherichia coli Aer Protein

et al. 2004

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Aer is a membrane-associated protein that mediates aerotactic responses in Escherichia coli. Its C-terminal half closely resembles the signaling domains of methyl-accepting chemotaxis proteins (MCPs), which undergo reversible methylation at specific glutamic acid residues to adapt their signaling outputs to homogeneous chemical environments. MCP-mediated behaviors are dependent on two specific enzymes, CheR (methyltransferase) and CheB (methylesterase). The Aer signaling domain contains unorthodox methylation sites that do not conform to the consensus motif for CheR or CheB substrates, suggesting that Aer, unlike conventional MCPs, might be a methylation-independent transducer. Several lines of evidence supported this possibility. (i) The Aer protein was not detectably modified by either CheR or CheB. (ii) Amino acid replacements at the putative Aer methylation sites generally had no deleterious effect on Aer function. (iii) Aer promoted aerotactic migrations on semisolid media in strains that lacked all four of the E. coli MCPs. CheR and CheB function had no influence on the rate of aerotactic movements in those strains. Thus, Aer senses and signals efficiently in the absence of deamidation or methylation, methylation changes, methylation enzymes, and methyl-accepting chemotaxis proteins. We also found that chimeric transducers containing the PAS-HAMP sensing domain of Aer joined to the signaling domain and methylation sites of Tar, an orthodox MCP, exhibited both methylationdependent and methylation-independent aerotactic behavior. The hybrid Aear transducers demonstrate that methylation independence does not emanate from the Aer signaling domain but rather may be due to transience of the cellular redox changes that are thought to trigger Aer-mediated behavioral responses.Methyl-accepting chemotaxis proteins (MCPs) mediate many of the chemotactic behaviors of bacteria and archaea (see references 6 and 20 for recent reviews). MCPs typically possess an extracellular ligand-binding domain for monitoring environmental chemoeffector levels and an intracellular signaling domain that controls motor responses and undergoes reversible methylation at multiple sites. Methylation enables MCPs to detect chemical changes over time by comparing current chemoeffector levels, reflected in the fraction of ligand-occupied molecules, with chemoeffector levels during the past few seconds, represented by the average methylation state of the molecules. Whenever current conditions differ from those of the recent past, MCPs produce a feedforward excitation signal that modulates the organism's motility and a feedback adaptation signal that updates MCP methylation state to correspond to the new chemical environment (see references 12 and 33 for recent reviews). The ability of MCPs to adapt to homogeneous chemical environments via methylation changes endows these chemoreceptors with a wide dynamic range for stimulus detection and signaling (45).Escherichia coli has four transmembrane MCPs that share a highly conserved signaling and methy...

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Aer and Tsr guide Escherichia coli in spatial gradients of oxidizable substrates

Cited by 47 publications

References 27 publications

How Phosphotransferase System-Related Protein Phosphorylation Regulates Carbohydrate Metabolism in Bacteria

How Phosphotransferase System-Related Protein Phosphorylation Regulates Carbohydrate Metabolism in Bacteria

An Energy Taxis Transducer Promotes Root Colonization byAzospirillum brasilense

Methylation-Independent Aerotaxis Mediated by the Escherichia coli Aer Protein

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