Fig. 3

The link between nitrogen metabolism and ectoine synthesis. Effect of the ect ⁻ mutation on the growth of C. salexigens. a The strains CHR61 (wild type, black symbols) and CHR62 (ect ⁻ mutant, white symbols) were grown in M63 glucose minimal medium with 0.75 M NaCl. b The defective growth phenotype of the mutant CHR62 strain was recovered upon growth in M63 glucose minimal medium supplemented with 20 mM ectoine as the sole nitrogen source. c Effect of the nitrogen source selected for the growth of C. salexigens. The wild type CHR61 strain was grown in in M63 minimal medium with 2.5 M NaCl and supplemented with 30 mM ammonium (black circles), 20 mM alanine (white triangles), 20 mM glutamate (black triangles) or 20 mM ectoine (white circles) as the sole nitrogen source. d Link between central metabolism and the ectoines biosynthesis pathway in C. salexigens [6]. Cofactors produced and/or consumed in each pathway are indicated. Glucose is transformed into pyruvate by the Entner–Doudoroff pathway and ectoines are synthesized from oxaloacetate and acetyl-CoA. e Ammonium assimilation pathways in C. salexigens: glutamate dehydrogenase (GDH) and glutamine synthetase/glutamate synthase (GS/GOGAT). Alanine is catabolized by oxidative deamination catalyzed by alanine dehydrogenase (AlaDH)*. f Overall stoichiometry of ectoine biosynthesis in C. salexigens as a function of the ammonium assimilation pathway used. Ectoine biosynthesis from glucose leads to net consumption of 1 mol of ATP if ammonia is assimilated through GDH and 3 mol of ATP if it is assimilated through the GS/GOGAT pathway**. * Genes encoding glutamate dehydrogenase (Csal1340) and alanine dehydrogenase (Csal2966) have been annotated in the genome of C. salexigens [23]. Five genes encoding putative glutamine synthetases are annotated: Csal0777, Csal1181, Csal1192, Csal0243, Csal0679. Glutamate synthase is a heterodimeric protein composed of two different subunits encoded by gltB (Csal0615) and gltD (Csal0616) genes. ** Hydroxyectoine biosynthesis from glucose needs additionally 1 mol NADH and 1 mol GTP due to the transformation of α-ketoglutarate into succinate by ectoine hydroxylase