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Open Access Research article

Involvement of EupR, a response regulator of the NarL/FixJ family, in the control of the uptake of the compatible solutes ectoines by the halophilic bacterium Chromohalobacter salexigens

Javier Rodríguez-Moya1, Montserrat Argandoña1, Mercedes Reina-Bueno1, Joaquín J Nieto1, Fernando Iglesias-Guerra2, Mohamed Jebbar34 and Carmen Vargas1*

  • * Corresponding author: Carmen Vargas cvargas@us.es

  • † Equal contributors

Author Affiliations

1 Department of Microbiology and Parasitology, Faculty of Pharmacy, University of Seville, Seville, Spain

2 Department of Organic and Pharmaceutical Chemistry. Faculty of Pharmacy, University of Seville, Seville, Spain

3 Laboratoire Interactions Cellulaires et Moléculaires, DUALS, CNRS 6026, Université de Rennes I, Campus Beaulieu, 35042 Rennes Cedex, France

4 Laboratoire de Microbiologie des Environnements Extrêmes - LM2E (CNRS), Université de Bretagne Occidentale, Plouzané, France

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BMC Microbiology 2010, 10:256  doi:10.1186/1471-2180-10-256

Published: 13 October 2010

Abstract

Background

Osmosensing and associated signal transduction pathways have not yet been described in obligately halophilic bacteria. Chromohalobacter salexigens is a halophilic bacterium with a broad range of salt tolerance. In response to osmotic stress, it synthesizes and accumulates large amounts of the compatible solutes ectoine and hydroxyectoine. In a previous work, we showed that ectoines can be also accumulated upon transport from the external medium, and that they can be used as carbon sources at optimal, but not at low salinity. This was related to an insufficient ectoine(s) transport under these conditions.

Results

A C. salexigens Tn1732-induced mutant (CHR95) showed a delayed growth with glucose at low and optimal salinities, could not grow at high salinity, and was able to use ectoines as carbon sources at low salinity. CHR95 was affected in the transport and/or metabolism of glucose, and showed a deregulated ectoine uptake at any salinity, but it was not affected in ectoine metabolism. Transposon insertion in CHR95 caused deletion of three genes, Csal0865-Csal0867: acs, encoding an acetyl-CoA synthase, mntR, encoding a transcriptional regulator of the DtxR/MntR family, and eupR, encoding a putative two-component response regulator with a LuxR_C-like DNA-binding helix-turn-helix domain. A single mntR mutant was sensitive to manganese, suggesting that mntR encodes a manganese-dependent transcriptional regulator. Deletion of eupR led to salt-sensitivity and enabled the mutant strain to use ectoines as carbon source at low salinity. Domain analysis included EupR as a member of the NarL/FixJ family of two component response regulators. Finally, the protein encoded by Csal869, located three genes downstream of eupR was suggested to be the cognate histidine kinase of EupR. This protein was predicted to be a hybrid histidine kinase with one transmembrane and one cytoplasmic sensor domain.

Conclusions

This work represents the first example of the involvement of a two-component response regulator in the osmoadaptation of a true halophilic bacterium. Our results pave the way to the elucidation of the signal transduction pathway involved in the control of ectoine transport in C. salexigens.