Specific growth inhibition by acetate of an Escherichia coli strain expressing Era-dE, a dominant negative Era mutant.

Escherichia coli Era is a GTP binding protein and essential for cell growth. We have previously reported that an Era mutant, designated Era-dE, causes a dominant negative effect on the growth and the loss of the ability to utilize TCA cycle metabolites as carbon source when overproduced. To investigate the role of Era, the gene expression in the cells overproducing Era-dE was examined by DNA microarray analysis. The expression of lipA and nadAB, which are involved in lipoic acid synthesis and NAD synthesis, respectively, was found to be reduced in the cells overproducing Era-dE. Lipoic acid and NAD are essential cofactors for the activities of pyruvate dehydrogenase complex, 2-oxoglutarate dehydrogenase complex and glycine cleavage enzyme complex. The expression of numerous genes involved in dissimilatory carbon metabolism and carbon source transport was increased. This set of genes partially overlaps with the set of genes controlled by cAMP-CAP in E coli. Moreover, the growth defect of Era-dE overproduction was specifically enhanced by acetate but not by TCA cycle metabolites both in rich and synthetic media. Intracellular serine pool in Era-dE overproducing cells was found to be increased significantly compared to that of the cells overproducing wild-type Era. It was further found that even the wild-type E. coli cells not overproducing Era-dE became sensitive to acetate in the presence of serine in a medium. We propose that when Era-dE is overproduced, carbon fluxes to the TCA cycle and to C1 units become impaired, resulting in a higher cellular serine concentration. We demonstrated that such cells with a high serine concentration became sensitive to acetate, however the reason for this acetate sensitivity is not known at the present.