Complex regulation of the synthesis of the compatible solute ectoine in the halophilic bacterium Chromohalobacter salexigens DSM 3043T.
The synthesis of the compatible solute ectoine, mediated by the ectABC gene products, is the main mechanism used by the halophilic bacterium Chromohalobacter salexigens to cope with osmotic stress. Evidence was found that this process is regulated at the transcriptional level. S1 protection analyses performed with RNA extracted from cells grown in minimal medium at low (0.75 M NaCl) or high (2.5 M NaCl) osmolarity suggested the existence of four promoters upstream of ectA. Two of these (PectA1 and PectA2) might be recognized by the main vegetative sigma factor sigma(70), and one (PectA3) might be dependent on the general stress sigma factor sigma(S). The S1 protection assays suggest that PectA1 and PectA3 may be osmoregulated promoters. In addition, an internal promoter showing sequences homologous to promoters dependent on the heat-shock sigma factor sigma(32) was found upstream of ectB. Transcription from PectA in C. salexigens followed a pattern typical of sigma(S)-dependent promoters, and was reduced by 50 % in an E. coli rpoS background. These data strongly suggest the involvement of the general stress sigma factor sigma(S) in ectABC transcription in C. salexigens. Expression of PectA-lacZ and PectB-lacZ trancriptional fusions was very high at low salinity, suggesting that ectABC may be a partially constitutive system. Both transcriptional fusions were induced during continuous growth at high temperature and their expression was reduced in cells grown in the presence of osmoprotectants (ectoine or glycine betaine) or the DNA gyrase inhibitor nalidixic acid. Moreover, PectA-lacZ expression was negatively modulated in cells grown with an excess of iron (FeCl(3)). Measurement of ectoine levels in the presence of glycine betaine at different NaCl concentrations suggests that an additional post-transcriptional control may occur as well.
Calderón
M Isabel
MI
Department of Microbiology and Parasitology, Faculty of Pharmacy, University of Seville, 41012 Seville, Spain.
Vargas
Carmen
C
Department of Microbiology and Parasitology, Faculty of Pharmacy, University of Seville, 41012 Seville, Spain.
Rojo
Fernando
F
Departamento de Biotecnología Microbiana, Centro Nacional de Biotecnología, CSIC, Campus de la Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid, Spain.
Iglesias-Guerra
Fernando
F
Department of Organic Chemistry and Pharmaceutical Chemistry, Faculty of Pharmacy, University of Seville, 41012 Seville, Spain.
Csonka
Laszlo N
LN
Department of Biological Sciences, Purdue University, West Lafayette, IN 47907-1392, USA.
Ventosa
Antonio
A
Department of Microbiology and Parasitology, Faculty of Pharmacy, University of Seville, 41012 Seville, Spain.
Nieto
Joaquín J
JJ
Department of Microbiology and Parasitology, Faculty of Pharmacy, University of Seville, 41012 Seville, Spain.
D000222:Adaptation, Physiological; D000599:Amino Acids, Diamino / Q000096:biosynthesis*; D019677:Artificial Gene Fusion; D001426:Bacterial Proteins / Q000235:genetics / Q000502:physiology; D001483:Base Sequence; D001622:Betaine / Q000494:pharmacology; D012321:DNA-Directed RNA Polymerases; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004926:Escherichia coli; D015964:Gene Expression Regulation, Bacterial; D017930:Genes, Reporter; D044129:Halomonadaceae / Q000235:genetics* / Q000378:metabolism*; D006360:Heat-Shock Proteins; D007763:Lac Operon; D008969:Molecular Sequence Data; D009268:Nalidixic Acid / Q000494:pharmacology; D009994:Osmolar Concentration; D009997:Osmotic Pressure; D011401:Promoter Regions, Genetic; D012329:RNA, Bacterial / Q000032:analysis / Q000378:metabolism; D012808:Sigma Factor / Q000235:genetics / Q000502:physiology; D013696:Temperature; D001616:beta-Galactosidase / Q000235:genetics / Q000378:metabolism
D000599:Amino Acids, Diamino; D001426:Bacterial Proteins; D004791:Enzyme Inhibitors; D006360:Heat-Shock Proteins; D012329:RNA, Bacterial; D012808:Sigma Factor; C069774:heat-shock sigma factor 32; C069567:sigma factor KatF protein, Bacteria; D009268:Nalidixic Acid; D001622:Betaine; C045628:ectoine; C081775:RNA polymerase sigma 70; D012321:DNA-Directed RNA Polymerases; D001616:beta-Galactosidase