Stationary Phase Expression of the Arginine Biosynthetic Operon (ARGCBH) in Escherichia Coli

Abstract

In this study, we report that expression of the 𝘢𝘳𝘨𝘊𝘉𝘏 operon is induced in stationary phase cultures and that this increase is largely dependent on RpoS, the alternative stress sigma factor. Using combinatorial 𝘢𝘳𝘨𝘙 and 𝘳𝘱𝘰𝘚 mutants, we evaluated the relative contributions of these two regulators to the expression of 𝘢𝘳𝘨𝘏 using operon 𝘭𝘢𝘤𝘡 fusions. While ArgR was found to be the main factor responsible for de-repression of the 𝘢𝘳𝘨𝘊𝘉𝘏 operon, RpoS was required for full expression of this biosynthetic operon at concentrations below 10 μg arginine ml⁻¹, a level at which growth of an arginine auxotroph was arginine limited. At high arginine concentrations (>10 μg ml⁻¹) 𝘢𝘳𝘨𝘊𝘉𝘏 expression was strongly repressed as expected by ArgR. 𝘢𝘳𝘨𝘊𝘉𝘏 expression was 30 fold higher in Δ𝘢𝘳𝘨𝘙 mutants relative to a wild type fully repressed strain and this expression was independent of RpoS. These results indicate that RpoS plays an important role in the regulation of arginine biosynthesis, particularly when the operon is partially de-repressed as would be the case in starvation conditions.