Oversynthesis of any cell metabolite, e.g., His, alters the carbon fluxes and pools of intermediate compounds, possibly resulting in consequences that are generally unpredictable. A study conducted to investigate specific features of L-histidine production by Escherichia coli concerned with feedback control of AICAR formation and inorganic phosphate/metal transport concluded that inhibition of a key enzyme in the His biosynthetic pathway, HisG, by AICAR, which is formed in this pathway, generates a serious bottleneck during His production. The constructed His-producing strain demonstrated the enhanced expression of genes that encode enzymes involved in the metabolism of AICAR to ATP, which is a substrate of HisG, and thus led to improved His accumulation. Kindly check the following RG link:

Article Specific features of L-histidine production by Escherichia c...

Also, kindly check the following RG link, that may be useful:

Biosynthesis of Histidine:

Article Biosynthesis of Histidine

Hi Lise,

Have you tested whether your E. coli strain (hisB-) without the plasmid carrying hisB can also grow in the selection media? This will indicate whether the problem is the E. coli strain (hisB-) or the promoter activation in the plasmid. You can also increase the concentration of 3-AT ( 3 mM or 5 mM) to impair the growth.

Good luck.

I'm not sure if it is about the cationic aminoacid. It stops bacteria (and above all ecoli)