Metabolic engineering of Saccharomyces cerevisiae for bioconversion of d-xylose to d-xylonate

Mervi Toivari, Yvonne Nygård, Esa-Pekka Kumpula, Maija-Leena Vehkomäki, Mojca Benčina, Mari Valkonen, Hannu Maaheimo, Martina Andberg, Anu Koivula, Laura Ruohonen, Merja Penttilä, Marilyn G. Wiebe

Index: Metab. Eng. 14(4) , 427-36, (2012)

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Abstract

An NAD+-dependent d-xylose dehydrogenase, XylB, from Caulobacter crescentus was expressed in Saccharomyces cerevisiae, resulting in production of 17±2g d-xylonate l−1 at 0.23gl−1h−1 from 23g d-xylose l−1 (with glucose and ethanol as co-substrates). d-Xylonate titre and production rate were increased and xylitol production decreased, compared to strains expressing genes encoding T. reesei or pig liver NADP+-dependent d-xylose dehydrogenases. d-Xylonate accumulated intracellularly to ∼70mgg−1; xylitol to ∼18mgg−1. The aldose reductase encoding gene GRE3 was deleted to reduce xylitol production. Cells expressing d-xylonolactone lactonase xylC from C. crescentus with xylB initially produced more extracellular d-xylonate than cells lacking xylC at both pH 5.5 and pH 3, and sustained higher production at pH 3. Cell vitality and viability decreased during d-xylonate production at pH 3.0. An industrial S. cerevisiae strain expressing xylB efficiently produced 43g d-xylonate l−1 from 49g d-xylose l−1.