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Appl. Environ. Microbiol. doi:10.1128/AEM.02858-07
Copyright (c) 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Engineering and analysis of a Saccharomyces cerevisiae strain that uses formaldehyde as an auxiliary substrate

Molecular Cell Biology, Groningen Biomolecular Sciences and Biotechnology Institute (GBB), University of Groningen, P.O. Box 14, 9750 AA Haren, The Netherlands; Department of Biotechnology, Delft University of Technology, Julianalaan 67, 2628 BC Delft, the Netherlands; Kluyver Centre for Genomics of Industrial Fermentation, Julianalaan 67, 2628 BC Delft, the Netherlands

^* To whom correspondence should be addressed. Email: j.t.pronk{at}tudelft.nl.

	Abstract

We demonstrate that formaldehyde can be efficiently co-utilized by an engineered S. cerevisiae strain that expresses Hansenula polymorpha genes encoding formaldehyde dehydrogenase (FLD1) and formate dehydrogenase (FMD) in contrast to wild type strains.

Initial chemostat experiments showed that the engineered strain co-utilized formaldehyde with glucose, but these mixed-substrate cultures failed to reach steady-state conditions and did not exhibit an increased biomass yield on glucose. Subsequent transcriptome analyses of chemostat cultures of the engineered strain, grown on glucose/formaldehyde mixtures, indicated that the presence of formaldehyde in the feed caused biotin limitations. Further transcriptome analysis demonstrated that this biotin inactivation was prevented by using separate formaldehyde and vitamin feeds. Using this approach, steady-state glucose-limited chemostat cultures were obtained that co-utilized glucose and formaldehyde. Co-utilization of formaldehyde under these conditions resulted in an enhanced biomass yield of the glucose-limited cultures.

The biomass yield was quantitatively consistent with the use of formaldehyde as an auxiliary substrate that generates NADH and subsequently, via oxidative phosphorylation, ATP. On an electron pair basis, the biomass yield increase observed with formaldehyde was larger than previously observed for formate, which is tentatively explained from different modes of formate and formaldehyde transport in S. cerevisiae.