Sinorhizobial chemotaxis: a departure from the enterobacterial paradigm a aTo Professor Wolfram Heumann on his 87th birthday.

Schmitt, Rüdiger

doi:10.1099/00221287-148-3-627

Cited by 45 publications

(49 citation statements)

References 36 publications

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“…This mechanism is in contrast to the behavior of E. coli, which relies on short-term reversals of rotation direction keeping its flagellar rotation speed rather constant. However, chemotaxis based solely on rotation speed modulation has been reported for Sinorhizobium meliloti (32), but this soil bacterium exhibits no true chemotaxis and relies clearly on temporal gradient sensing. Furthermore, the fact that the ends of the vibrioid cells traces a left-handed helix implies that the flagella rotate clockwise if seen from behind, whereas the flagella of other bacteria such as E. coli typically rotate counter-clockwise during straight swimming paths (5).…”

Section: Resultsmentioning

confidence: 99%

Bacteria are not too small for spatial sensing of chemical gradients: An experimental evidence

Thar

Kühl

2003

Proc. Natl. Acad. Sci. U.S.A.

105

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By analyzing the chemotactic behavior of a recently described marine bacterial species, we provide experimental evidence that bacteria are not too small for sensing chemical gradients spatially. The bipolar flagellated vibrioid bacteria (typical size 2 ؋ 6 m) exhibit a unique motility pattern as they translate along as well as rotate around their short axis, i.e., the pathways of the cell poles describe a double helix. The natural habitat of the bacteria is characterized by steep oxygen gradients where they accumulate in a band at their preferred oxygen concentration of Ϸ2 M. Single cells leaving the band toward the oxic region typically return to the band within 16 s following a U-shaped track. A detailed analysis of the tracks reveals that the cells must be able to sense the oxygen gradient perpendicular to their swimming direction. Thus, they can detect oxygen gradients along a distance of Ϸ5 m corresponding to the extension of their long axis. The observed behavior can be explained by the presence of two independent sensor regions at either cell pole that modulate the rotation speed of the polar flagellar bundles, i.e., the flagellar bundle at the cell pole exposed to higher oxygen concentration is rotating faster than the other bundle. A mathematical model based on these assumptions reproduces the observed swimming behavior of the bacteria. F lagellar motility is widespread among prokaryotes living in aquatic environments, and it is estimated that 20% of marine planktonic bacteria are motile (1). Generally, bacteria exhibit motility to find places in their environment where they can maximize their substrate or energy uptake. To achieve this, they have to modulate their motility in response to environmental variables (2). When cell motility is modulated via sensing of chemical signals in the environment, the resulting motility behavior is termed chemotaxis. Best understood is the chemotactic behavior of the flagellated enteric bacterium Escherichia coli (reviewed in refs. 3-5). More or less straight swimming paths (caused by synchronous counter-clockwise rotation of all flagella) are interrupted periodically by random direction changes: so-called tumbles caused by short-term direction reversals of one or more flagella. Chemical attractants or repellants bind to specific receptor protein complexes at the cell surface, which subsequently inhibit or promote, respectively, the phosphorylation of an intracellular freely diffusing signaling protein. The flagellar motors respond to increased phosphorylation levels of the signaling protein with more frequent reversals of flagellar rotation causing more frequent tumbling of the bacteria. Additionally, a dynamic methylation of the receptor protein complexes provides an adaptation mechanism, ensuring that the chemotactic behavior is functioning over a wide range of attractant or repellant concentrations. If a bacterium experiences increasing attractant (or decreasing repellant) concentrations along its swimming path, the described mechanism results in less-frequent ran...

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Section: Resultsmentioning

confidence: 99%

Bacteria are not too small for spatial sensing of chemical gradients: An experimental evidence

Thar

Kühl

2003

Proc. Natl. Acad. Sci. U.S.A.

105

View full text Add to dashboard Cite

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“…In the first, the type-A ARRs may compete with positively acting type-B ARRs for phosphoryl transfer from the upstream AHPs, similar to the chemotaxis system in Sinorhizobium meliloti (Schmitt, 2002). A second model is that type-A ARRs regulate the pathway through direct or indirect interactions with pathway components, as observed in Escherichia coli chemotaxis (Bourret and Stock, 2002).…”

Section: Introductionmentioning

confidence: 99%

Cytokinin Regulates Type-A Arabidopsis Response Regulator Activity and Protein Stability via Two-Component Phosphorelay

et al. 2007

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The plant hormone cytokinin regulates many aspects of growth and development. Cytokinin signaling involves His kinase receptors that perceive cytokinin and transmit the signal via a multistep phosphorelay similar to bacterial two-component signaling systems. The final targets of this phosphorelay are a set of Arabidopsis thaliana Response Regulator (ARR) proteins containing a receiver domain with a conserved Asp phosphorylation site. One class of these, the type-A ARRs, are negative regulators of cytokinin signaling that are rapidly transcriptionally upregulated in response to cytokinin. In this study, we tested the role of phosphorylation in type-A ARR function. Our results indicate that phosphorylation of the receiver domain is required for type-A ARR function and suggest that negative regulation of cytokinin signaling by the type-A ARRs most likely involves phosphorylation-dependent interactions. Furthermore, we show that a subset of the type-A ARR proteins are stabilized in response to cytokinin in part via phosphorylation. These studies shed light on the mechanism by which type-A ARRs act to negatively regulate cytokinin signaling and reveal a novel mechanism by which cytokinin controls type-A ARR function.

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“…However, only one CheY protein (CheY2) interacts with the flagellar motor when phosphorylated and, therefore, controls flagellar rotation directly, while the second CheY protein (CheY1) functions as a modulator of the chemotactic response by acting as a phosphate sink which drains away the phosphoryl group from CheY2~P via retro-phosphorylation of the histidine kinase CheA. Since CheY1 is present in S. meliloti in a tenfold excess over CheA, retro-phosphorylation in the signal transduction chain is an efficient mechanism for dephosphorylation of CheY2~P (Schmitt, 2002).…”

Section: Introductionmentioning

confidence: 99%

Phosphate flow in the chemotactic response system of Helicobacter pylori

et al. 2005

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It is well established that motility is an essential virulence trait of the human gastric pathogen Helicobacter pylori. Accordingly, chemotaxis contributes to the ability of H. pylori to colonize animal infection models. Chemotactic signal transduction in H. pylori differs from the enterobacterial paradigm in several respects. In addition to a separate CheY response regulator protein (CheY1), H. pylori contains a CheY-like receiver domain (CheY2) which is C-terminally fused to the histidine kinase CheA. Furthermore, the genome of H. pylori encodes three CheV proteins consisting of an N-terminal CheW-like domain and a C-terminal receiver domain, while there are no orthologues of the chemotaxis genes cheB, cheR and cheZ. To obtain insight into the mechanisms controlling the chemotactic response of H. pylori, we investigated the phosphotransfer reactions between the purified two-component signalling modules in vitro. We demonstrate that both CheY1 and CheY2 are phosphorylated by CheA∼P and that the three CheV proteins mediate the dephosphorylation of CheA∼P, but with a clearly reduced efficiency as compared to CheY1 and CheY2. Furthermore, our data indicate retrophosphorylation of CheAY2 by CheY1∼P, suggesting a role of CheY2 as a phosphate sink to modulate the half-life of CheY1∼P.

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Sinorhizobial chemotaxis: a departure from the enterobacterial paradigm a aTo Professor Wolfram Heumann on his 87th birthday.

Cited by 45 publications

References 36 publications

Bacteria are not too small for spatial sensing of chemical gradients: An experimental evidence

Bacteria are not too small for spatial sensing of chemical gradients: An experimental evidence

Cytokinin Regulates Type-A Arabidopsis Response Regulator Activity and Protein Stability via Two-Component Phosphorelay

Phosphate flow in the chemotactic response system of Helicobacter pylori

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