Expression of cadaverine biosynthesis genes under superoxide oxidative stress

The effect of redox-cycling methyl viologen, which causes the production of superoxide and formation of oxidative stress in bacterial cells, on the expression of the cadA and ldcC genes was studied. Gene expression was assessed using Escherichia coli strains bearing reporter gene fusions of the promoters of the studied genes with the structural part of the lacZ gene; expression values are given in Miller units. Bacteria were grown in batch cultures in LB broth without agitation or with agitation at 100 r.p.m. We have shown that exposure to methyl viologen, which leads to the induction of the nfo gene included in the soxRS regulon of oxidative defense (a long-term increase in the expression level by 10 times), led to a slight and short-term increase in the expression of the cadA and ldcC genes (by a maximum of 1.4 times, no longer than 1 h). An increase in the strength of oxidative stress due to elevated agitation/aeration had no effect on the expression of the cadA and ldcC genes. Methyl viologen at the concentrations used (1-100 μg/mL) did not affect the number of colony-forming units in the culture. Thus, non-lethal superoxide stress caused by exposure of bacteria to methyl viologen had little effect on the expression of the ldcC and cadA genes compared to the genes included in the soxRS regulon, which were strongly induced under these conditions.