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

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.