Chromohalobacter Salexigens

A Microbial Biorealm page on the genus Chromohalobacter Salexigens

Classification

Higher order taxa

Bacteria; Proteobacteria; Gammaproteobacteria; Oceanospirillales; Halomonadaceae; Chromohalobacter;

NCBI: Taxonomy Genome

Species

C. Salexigens

Description and significance

Genome Sequence of C. Salexigens. Courtesy ofBacMap Genome Atlas

This bacterium is a moderate halophile(salt loving), yet does not require high concentrations of sodium chloride. C. Salexigens is very flexible in that its salt requirements can be met by ions of other salts such as potassium, rubidium, ammonium, bromide, and others.

Genome structure

DNA Bases: 3696649

Chromosome Type: Circular

Total Genes: 3403

Protein Coding Genes: 3319
RNA Genes:              84
Pseudo Genes:           21

Cell structure and metabolism

The growth rate of Chromohalobacter salexigens DSM 3043 can be stimulated in media containing 0.3 M NaCl by a 0.7 M concentration of other salts of Na+, K+, Rb+, or NH4+, Cl-, Br-, NO3-, or SO4(2-) ions.

Edit: Placing Chromohalobacter salexigens in media containing a 0.3M concentration of NaCL and a 0.7M concentration of (Na+, K+, Rb+, etc...) will stimulate its growth positively.

Ecology

Describe any interactions with other organisms (included eukaryotes), contributions to the environment, effect on environment, etc.

Pathology

Current research indicates that C. Salexigens is not known to be pathogenic.

Application to Biotechnology

The bacterium C. Salexigens synthesizes and accumulates compatible solutes in response to salt and temperature stress. The ectD gene, which is involved in the synthesis of the compatible solute hydroxyectoine, is essential for thermoprotection of the halophilic bacterium Chromohalobacter salexigens.

Edit: In response to salt and temperature stress C. Salexigens produces and stores various solutes. Some solutes, namely hydroxyectoine, are used in thermoregulation processes that protect C. Salexigens from extreme temperatures.

Current Research

N(gamma)-acetyl-2,4-diaminobutyrate (NADA), the precursor of the compatible solute ectoine, was shown to function as an osmoprotectant for the non-halophilic bacterium Salmonella enterica serovar Typhimurium. The addition of NADA-containing extracts of an ectoine synthase mutant of the broad salt-growing halophile Chromohalobacter salexigens DSM 3043(T) could alleviate the inhibitory effects of high salinity in S. enterica, which lacks the ectoine biosynthetic pathway. NADA, purified from extracts of the mutant, protected S. enterica against salinity stress.

In another study, the long-term response of the broad-salt growing halophile Chromohalobacter salexigens DSM 3043T to salt stress has been investigated with respect to adaptive changes in membrane lipid composition. This study included the wild-type and three salt-sensitive, ectoine-deficient strains: CHR62 (ectA::Tn1732, unable to grow above 0.75 M NaCl), CHR63 (ectC::Tn1732, unable to grow above 1.5 M NaCl), and CHR64, which was able to grow in minimal medium M63 up to 2.5 M NaCl, but its growth was slower than the wild-type strain at salinities above 1.5 M NaCl. This mutant accumulated ectoine and hydroxyectoine as major compatible solutes, but also the ectoine precursor, N-gamma-acetyldiaminobutyric acid, and was found to be affected in the ectoine synthase gene ectC. The main phospholipids of the wild-type strain were phosphatidylethanolamine, phosphatidylglycerol (PG), and cardiolipin (CL). Major fatty acids were detected as 16:0, 18:1, and 16:1, including significant amounts of cyc-19:0, and cyc-17:0. CL and cyclopropane fatty acids (CFA) levels were elevated when the wild-type strain was grown at high salinity (2.5 M NaCl). Membranes of the most salt-sensitive trains CHR62 and CHR63, but not of the less salt-sensitive strain CHR64, contained lower levels of CL. The proportion of cyc-19:0 in CHR64 was three-fold (at 2.0M NaCl) and 2.5-fold (at 2.5 M NaCl) lower than that of the wild type, suggesting that this mutant has a limited capacity to incorporate CFA into phospholipids at high salt. The addition of 1 mM ectoine to cultures of the wild-type strain increased the ratio PG/CL from 1.8 to 3.3 at 0.75 M NaCl, and from 1 to 6.5 at 2.5 M NaCl, and led to a slight decrease in CFA content. Addition of 1 mM ectoine to the mutants restored the steady-state levels of CL and CFA found in the wild-type strain supplemented with ectoine. These findings suggest that exogenous ectoine might attenuate the osmostress response involving changes in membrane lipids.