Engineering of Corynebacterium glutamicum for minimized carbon loss during utilization of D-xylose containing substrates.

Biomass-derived d-xylose represents an economically interesting substrate for the sustainable microbial production of value-added compounds. The industrially important platform organism Corynebacterium glutamicum has already been engineered to grow on this pentose as sole carbon and energy source. However, all currently described C. glutamicum strains utilize d-xylose via the commonly known isomerase pathway that leads to a significant carbon loss in the form of CO2, in particular, when aiming for the synthesis of α-ketoglutarate and its derivatives (e.g. l-glutamate). Driven by the motivation to engineer a more carbon-efficient C. glutamicum strain, we functionally integrated the Weimberg pathway from Caulobacter crescentus in C. glutamicum. This five-step pathway, encoded by the xylXABCD-operon, enabled a recombinant C. glutamicum strain to utilize d-xylose in d-xylose/d-glucose mixtures. Interestingly, this strain exhibited a tri-phasic growth behavior and transiently accumulated d-xylonate during d-xylose utilization in the second growth phase. However, this intermediate of the implemented oxidative pathway was re-consumed in the third growth phase leading to more biomass formation. Furthermore, C. glutamicum pEKEx3-xylXABCDCc was also able to grow on d-xylose as sole carbon and energy source with a maximum growth rate of μmax=0.07±0.01h(-1). These results render C. glutamicum pEKEx3-xylXABCDCc a promising starting point for the engineering of efficient production strains, exhibiting only minimal carbon loss on d-xylose containing substrates.