科研之友
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摘要
As a promising brown macroalgal carbohydrate, mannitol has been an alternative renewable feedstock for biofuel and biochemical production, avoiding competition with food production for natural resources. In this study, we describe a cell factory of the evolved Saccharomyces cerevisiae based on adaptive laboratory evolution that efficiently biotransforms mannitol into the high value-added sesquiterpenoid valencene. The evolved S. cerevisiae BN-91A with a series of mutations in the genome exhibited superior performance in mannitol assimilation, with the expression levels of genes involved in mannitol assimilation being dramatically upregulated by 50-480 fold. When grown on mannitol, the BN-91A strain showed a valencene titer of 17.2 mg L-1 and a carbon conversion efficiency of 1.905 mg g(-1), which were approximately 3-fold and 7-fold higher than those on glucose, respectively. Further analysis of the valencene synthase coding gene revealed an elevation of its gene dose and transcriptional level under mannitol conditions, which were 3-fold and 5-fold as much as those under glucose conditions, respectively. Moreover, the valencene titer of BN-91A had little to no impact upon salt shock, indicating the competence of BN-91A to produce valencene from macroalgae-derived mannitol. An improved valencene titer of 161.1 mg L-1 was obtained in flasks after applying a combinational engineering strategy including precursor supply enhancement, mannitol uptake facilitation and cofactor regeneration acceleration. Finally, a maximum valencene titer of 5.61 g L-1 was obtained in a fed-batch bioreactor with mannitol feeding. Our findings establish a novel strategy of terpenoid production in S. cerevisiae, which opens a new avenue for application of third-generation renewable biomass marine macroalgae.
