Effect of transport proteins on l-isoleucine production with the l-isoleucine-producing strain Corynebacterium glutamicum YILW

Abstract

Abstract Previous studies have shown that the deletion of brnQ from the Corynebacterium glutamicum chromosome results in a significant reduction in l-isoleucine uptake rates, while overexpression of brnFE leads to enhanced l-isoleucine export rates. Given that net excretion rates would be an important factor for high titers of l-isoleucine accumulation, we have tested the notion that decreased l-isoleucine uptake combined with increased l-isoleucine excretion will further improve high-yield strains that are currently used for the industrial-scale production of l-isoleucine. To examine the effect of the two carriers on l-isoleucine accumulation in l-isoleucine producer C. glutamicum YILW, we constructed a brnQ deletion mutant (C. glutamicum YILW∆brnQ) and two brnFE overexpressors (C. glutamicum YILWpXMJ19brnFE and C. glutamicum YILW∆brnQpXMJ19brnFE). Compared to the original strain, the efflux rate of the brnQ mutant increased from 19.0 to 23.6 nmol min−1 mg (dry wt)−1 and its l-isoleucine titer increased from 154.3 mM (20.2 g l−1) to 170.3 mM (22.3 g l−1). The efflux rates of C. glutamicum YILWpXMJ19brnFE and C. glutamicum YILW∆brnQpXMJ19brnFE were 33.5 and 39.1 nmol min−1 mg (dry wt)−1, and their l-isoleucine production titers were 197.2 mM (25.9 g l−1) and 221.0 mM (29.0 g l−1), respectively. Our results suggest that modifications of the transport system could provide a promising avenue for further increasing l-isoleucine yield in the l-isoleucine producer.