Metabolic response of Haloferax mediterranei to different amino acids as a nitrogen source: from rich to limiting nitrogen conditions

Haloferax mediterranei, a halophilic archaeon, exhibits remarkable adaptability to nitrogen availability by using a wide range of nitrogen sources, including inorganic compounds and single amino acids. To investigate the organism's transcriptional response to different nitrogen conditions, transcriptome analyses were performed with cells grown in nitrate, ammonium, or nitrogen-starvation conditions. The data revealed that nitrate as a nitrogen source induces the up-regulation of genes involved in amino acid catabolism (isoleucine, leucine, and aspartate) while simultaneously repressing genes involved in amino acid biosynthesis. To further explore this metabolic plasticity, a second transcriptomic study was conducted with cultures grown with ammonium or single amino acids (glutamate, glutamine, aspartate, and asparagine) as sole nitrogen sources. The expression profiles indicated metabolic adjustments in response to these alternative nitrogen sources, including activation of high-affinity ammonium transporters, nitrate assimilation, the GS-GOGAT pathway, carbon flux rerouting, exopolysaccharide synthesis, and repression of energy metabolism and the translational machinery. These results highlight the ability of H. mediterranei to fine-tune its nitrogen metabolism in response to both inorganic and organic nitrogen sources. This work provides new insights into the nitrogen metabolism of H. mediterranei and offers a deeper understanding of its potential for biotechnological applications under nutrient-limited conditions.