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

Abstract

BackgroundOsmosensing 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.ResultsA 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.ConclusionsThis 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.

Phenotypic Heterogeneity of Genomically-Diverse Isolates of Streptococcus mutans

“…The sensor HK protein is predicted to contain 10 transmembrane domains, and is classified as a membrane-sensing HK and can be further classified into subgroup (ii) as a quorum-sensing HK with ComD (TCS-13). The response regulator (RR) of this novel HK/RR pair contains a LuxR_C-like DNA-binding HTH domain and was classified as a NarL type RR, which in other bacteria are involved in the control of genes that affect nitrogen fixation, sugar phosphate transport, nitrate and nitrite metabolism, quorum sensing or osmotic stress tolerance [72]. The function of this TCS in S. mutans has yet to be determined.…”

Ectoine and Hydroxyectoine as Protectants against Osmotic and Cold Stress: Uptake through the SigB-Controlled Betaine-Choline- Carnitine Transporter-Type Carrier EctT from Virgibacillus pantothenticus

“…Its induction by salt and cold stress points to the use of this compound as a stress protectant rather than as a nutrient. Indeed, in contrast to several other microorganisms (26,36,48), V. pantothenticus cannot use ectoine or hydroxyectoine as sole sources of carbon or nitrogen.…”

Role of the Extremolytes Ectoine and Hydroxyectoine as Stress Protectants and Nutrients: Genetics, Phylogenomics, Biochemistry, and Structural Analysis

“…There have been no follow-up studies on this hypothetical 5-hydroxyectoine biosynthetic route since it was originally proposed by Canovas et al, in 1999 [ 179 ]. Synthesis of ectoine and 5-hydroxyectoine in the ectC mutant may be a particular feature of the studied C. salexigens genetic background [ 120 , 179 ], or the fact that C. salexigens is also able to catabolize ectoines [ 80 , 190 ] and may thus use some of the degradative enzymes (see Section 7 ) to partially restore ectoine/5-hydroxyectoine production.…”