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Background    Escherichia coli  suffer from osmotic stress during succinic acid (SA) production, which reduces the performance of this microbial factory.    Results  Here, we report that a point mutation leading to a single amino acid change (D654Y) within the β-subunit of DNA-dependent RNA polymerase (RpoB) significantly improved the osmotolerance of  E. coli . Importation of the D654Y mutation of RpoB into the parental strain, Suc-T110, increased cell growth and SA production by more than 40% compared to that of the control under high glucose osmolality. The transcriptome profile, determined by RNA-sequencing, showed two distinct stress responses elicited by the mutated RpoB that counterbalanced the osmotic stress. Under non-stressed conditions, genes involved in the synthesis and transport of compatible solutes such as glycine-betaine, glutamate or proline were upregulated even without osmotic stimulation, suggesting a “pre-defense” mechanism maybe formed in the  rpoB  mutant. Under osmotic stressed conditions, genes encoding diverse sugar transporters, which should be down-regulated in the presence of high osmotic pressure, were derepressed in the  rpoB  mutant. Additional genetic experiments showed that enhancing the expression of the  mal  regulon, especially for genes that encode the glycoporin LamB and maltose transporter, contributed to the osmotolerance phenotype.    Conclusions  The D654Y single amino acid substitution in RpoB rendered  E. coli  cells resistant to osmotic stress, probably due to improved cell growth and viability via enhanced sugar uptake under stressed conditions, and activated a potential “pre-defense” mechanism under non-stressed conditions. The findings of this work will be useful for bacterial host improvement to enhance its resistance to osmotic stress and facilitate bio-based organic acids production.    Electronic supplementary material  The online version of this article (doi:10.1186/s12896-017-0337-6) contains supplementary material, which is available to authorized users.

A novel point mutation in RpoB improves osmotolerance and succinic acid production in Escherichia coli