Unravelling the adaptation responses to osmotic and temperature stress in Chromohalobacter salexigens, a bacterium with broad salinity tolerance

Abstract

Chromohalobacter salexigens, a Gammaproteobacterium belonging to the family Halomonadaceae, shows a broad salinity range for growth. Osmoprotection is achieved by the accumulation of compatible solutes either by transport (betaine, choline) or synthesis (mainly ectoine and hydroxyectoine). Ectoines can play additional roles as nutrients and, in the case of hydroxyectoine, in thermotolerance. A supplementary solute, trehalose, not present in cells grown at 37°C, is accumulated at higher temperatures, suggesting its involvement in the response to heat stress. Trehalose is also accumulated at 37°C in ectoine-deficient mutants, indicating that ectoines suppress trehalose synthesis in the wild-type strain. The genes for ectoine (ectABC) and hydroxyectoine (ectD, ectE) production are arranged in three different clusters within the C. salexigens chromosome. In order to cope with changing environment, C. salexigens regulates its cytoplasmic pool of ectoines by a number of mechanisms that we have started to elucidate. This is a highly complex process because (i) hydroxyectoine can be synthesized by other enzymes different to EctD (ii) ectoines can be catabolized to serve as nutrients, (iii) the involvement of several transcriptional regulators (σ S , σ 32 , Fur, EctR) and hence different signal transduction pathways, and (iv) the existence of post-trancriptional control mechanisms. In this review we summarize our present knowledge on the physiology and genetics of the processes allowing C. salexigens to cope with osmotic stress and high temperature, with emphasis on the transcriptional regulation.

A Specialized Aspartokinase Enhances the Biosynthesis of the Osmoprotectants Ectoine and Hydroxyectoine in Pseudomonas stutzeriA1501

“…Colocalization of the ectoine/hydroxyectoine biosynthetic genes and of ask_ect is not uncommon in microorganisms (39,45,57,62). We extend previous analysis by inspecting the presently available bacterial (1,426) and archaeal (80) genome sequences for ask_ect genes associated with ectoine/hydroxyectoine biosynthetic gene clusters.…”

“…This finding hints that this particular ask gene (ask_ect) encodes an aspartokinase that could play a specialized role in the biosynthesis of the compatible solute ectoine under osmotic stress conditions. Subsequently, it was observed that a considerable number of ectoine/hydroxyectoine biosynthetic gene clusters are actually followed by an ask gene (39,45,57,62). A comprehensive cohesion group analysis reported by Lo et al (39) showed that the encoded proteins form a distinct subcluster (cohesion group 02 [CG-02]) within the Ask superfamily.…”

“…The ectABC operon might also contain the structural gene (ectD) for the ectoine hydroxylase (8,48), but this gene can often also be found in a genomic location unlinked from the ectoine biosynthetic gene cluster (9,17). Database searches by different groups have shown that the ability to synthesize ectoine and hydroxyectoine is widespread in the microbial world (9,39,45,50,62). Our updated database searches of microbial genomes that are completely sequenced (currently more then 1,400 entries) using the ectoine synthase EctC as a search template show that 220 microorganisms are likely ectoine producers, and about a third of these are predicted to synthesize hydroxyectoine as well (M. Pittelkow and E. Bremer, unpublished data).…”

Genetic and Biochemical Aspects of Ectoine Biosynthesis in Moderately Halophilic and Halotolerant Methylotrophic Bacteria

“…However, the putative regulatory protein is disrupted by two stop codons and no start codon could be found. In C. salexigens, the orf (gene ectR) was found upstream of ectD (Vargas et al, 2008;Garcia-Estepa et al, 2006). Deletion of the ectR gene resulted in decreasing of hydroxyectoine level at high salinity and high temperature, in comparison to the wild type cells.…”

Genome-Wide Relative Analysis of Codon Usage Bias and Codon Context Pattern in the Bacteria Salinibacter Ruber, Chromohalobacter Salexigens and Rhizobium Etli

“…C. salexigens, a gram-negative aerobic bacterium, is moderately halophilic in nature. It grows at NaCl concentrations ranging between 0.5M and 4M, with an optimum growth at 2.0-2.5M and at an optimum temperature of 37°C [6,7]. Rhizobium etli (R. etli) is gram-negative soil bacteria, which fixes nitrogen and forms an endosymbiosis nitrogen fixing association with roots of legumes.…”