Metabolic engineering of Corynebacterium glutamicum for fatty alcohol production from glucose and wheat straw hydrolysate

Background: Fatty acid-derived products such as fatty alcohols (FAL) find growing application in cosmetic products, lubricants, or biofuels. So far, FAL are primarily produced petrochemically or through chemical conversion of bio-based feedstock. Besides the well-known negative environmental impact of using fossil resources, utilization of bio-based first-generation feedstock such as palm oil is known to contribute to the loss of habitat and biodiversity. Thus, the microbial production of industrially relevant chemicals such as FAL from second-generation feedstock is desirable. Results: To engineer Corynebacterium glutamicum for FAL production, we deregulated fatty acid biosynthesis by deleting the transcriptional regulator gene fasR, overexpressing a fatty acyl-CoA reductase (FAR) gene of Marinobacter hydrocarbonoclasticus VT8 and attenuating the native thioesterase expression by exchange of the ATG to a weaker TTG start codon. C. glutamicum ∆fasR cg2692_TTG (pEKEx2-maqu2220) produced in shaking flasks 0.54 ± 0.02 g_FAL L⁻¹ from 20 g glucose L⁻¹ with a product yield of 0.054 ± 0.001 Cmol Cmol⁻¹. To enable xylose utilization, we integrated xylA encoding the xylose isomerase from Xanthomonas campestris and xylB encoding the native xylulose kinase into the locus of actA. This approach enabled growth on xylose. However, adaptive laboratory evolution (ALE) was required to improve the growth rate threefold to 0.11 ± 0.00 h⁻¹. The genome of the evolved strain C. glutamicum gX was re-sequenced, and the evolved genetic module was introduced into C. glutamicum ∆fasR cg2692_TTG (pEKEx2-maqu2220) which allowed efficient growth and FAL production on wheat straw hydrolysate. FAL biosynthesis was further optimized by overexpression of the pntAB genes encoding the membrane-bound transhydrogenase of E. coli. The best-performing strain C. glutamicum ∆fasR cg2692_TTG CgLP12::(P_tac-pntAB-T_rrnB) gX (pEKEx2-maqu2220) produced 2.45 ± 0.09 g_FAL L⁻¹ with a product yield of 0.054 ± 0.005 Cmol Cmol⁻¹ and a volumetric productivity of 0.109 ± 0.005 g_FAL L⁻¹ h⁻¹ in a pulsed fed-batch cultivation using wheat straw hydrolysate. Conclusion: The combination of targeted metabolic engineering and ALE enabled efficient FAL production in C. glutamicum from wheat straw hydrolysate for the first time. Therefore, this study provides useful metabolic engineering principles to tailor this bacterium for other products from this second-generation feedstock.