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Journal of Bacteriology, March 2007, p. 1816-1826, Vol. 189, No. 5
0021-9193/07/$08.00+0     doi:10.1128/JB.00883-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Functional Analysis of Nine Putative Chemoreceptor Proteins in Sinorhizobium meliloti{triangledown} ,{dagger}

Veronika M. Meier, Paul Muschler,{ddagger} and Birgit E. Scharf*

Lehrstuhl für Genetik, Universität Regensburg, D-93040 Regensburg, Germany

Received 20 June 2006/ Accepted 12 December 2006

The genome of the symbiotic soil bacterium Sinorhizobium meliloti contains eight genes coding for methyl-accepting chemotaxis proteins (MCPs) McpS to McpZ and one gene coding for a transducer-like protein, IcpA. Seven of the MCPs are localized in the cytoplasmic membrane via two membrane-spanning regions, whereas McpY and IcpA lack such hydrophobic regions. The periplasmic regions of McpU, McpV, and McpX contain the small-ligand-binding domain Cache. In addition, McpU possesses the ligand-binding domain TarH. By probing gene expression with lacZ fusions, we have identified mcpU and mcpX as being highly expressed. Deletion of any one of the receptor genes caused impairments in the chemotactic response toward most organic acids, amino acids, and sugars in a swarm plate assay. The data imply that chemoreceptor proteins in S. meliloti can sense more than one class of carbon source and suggest that many or all receptors work as an ensemble. Tactic responses were virtually eliminated for a strain lacking all nine receptor genes. Capillary assays revealed three important sensors for the strong attractant proline: McpU, McpX, and McpY. Receptor deletions variously affected free-swimming speed and attractant-induced chemokinesis. Noticeably, cells lacking mcpU were swimming 9% slower than the wild-type control. We infer that McpU inhibits the kinase activity of CheA in the absence of an attractant. Cells lacking one of the two soluble receptors were impaired in chemokinetic proficiency by more than 50%. We propose that the internal sensors, IcpA and the PAS domain containing McpY, monitor the metabolic state of S. meliloti.

* Corresponding author. Mailing address: Lehrstuhl für Genetik, Universität Regensburg, D-93040 Regensburg, Germany. Phone: 49 (941) 9433170. Fax: 49 (941) 9433163. E-mail: birgit.scharf{at}biologie.uni-regensburg.de.

{triangledown} Published ahead of print on 22 December 2006.

{dagger} Dedicated to Rüdiger Schmitt on the occasion of his 70th birthday.

{ddagger} Present address: Promega GmbH, 68199 Mannheim, Germany.

Journal of Bacteriology, March 2007, p. 1816-1826, Vol. 189, No. 5
0021-9193/07/$08.00+0     doi:10.1128/JB.00883-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Meier, V. M., Scharf, B. E. (2009). Cellular Localization of Predicted Transmembrane and Soluble Chemoreceptors in Sinorhizobium meliloti. J. Bacteriol. 191: 5724-5733 [Abstract] [Full Text]  
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  • Gibson, K. E., Barnett, M. J., Toman, C. J., Long, S. R., Walker, G. C. (2007). The Symbiosis Regulator CbrA Modulates a Complex Regulatory Network Affecting the Flagellar Apparatus and Cell Envelope Proteins. J. Bacteriol. 189: 3591-3602 [Abstract] [Full Text]  


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