Expression of global regulator IrrE for improved succinate production under high salt stress by Escherichia coli.

Poor high salt stress resistance remained as a main hurdle limiting the efficient bio-based succinic acid production. In this study, the metabolically engineered E. coli not only showed improvement of high salt stress tolerance through expression of a global regulator IrrE, but also could use seawater for succinic acid fermentation. The recombinant strain showed an increased 1.20-fold of cell growth rate and 1.24-fold of succinic acid production. Expression levels of genes related glucose uptake and succinic acid synthesis were up-regulated, and more glycerol and trehalose were accumulated. Moreover, no significant differences were observed in cell growth even when tap water was replaced by 60% artificial seawater. In the fermentation using Yellow Sea seawater, 24.5 g/L succinic acid was achieved with a yield of 0.88 g/g. This strategy set up a platform for improving abiotic stress tolerances and provide a possible approach for fermentation processes with low cost.

[Influence of expressing IrrE from Deinococcus radiodurans on osmotic stress tolerance of succinate-producing Escherichia coli].

Hyper-osmotic stress is one of the key factors that decrease the efficiency of biological succinic acid production. To increase the osmotic stress tolerance of succinate-producing Escherichia coli, we studied the influence of IrrE, an exogenous global regulator, on cell osmotic stress resistance. Fermentation results showed that cell growth and succinic acid production by the recombinant increased under different Na+ concentrations. Meanwhile, the maximum dry cell mass, glucose consumption and succinic acid concentration increased 15.6%, 22% and 23%, respectively, when fermented in a 5-L bioreactor. Expressing IrrE improved cell resistance to hyper-osmotic stress. Further comparison of intracellular osmoprotectants (trehalose and glycerol) concentrations showed that trehalose and glycerol concentrations in the recombinant increased. This suggested that introduction of IrrE could enhance intracellular osmoprotectants accumulation which conferred cell with improved resistance to osmotic stress.