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Background  Cold stress reduces microbial growth and metabolism being relevant in industrial processes like wine making and brewing. Knowledge on the cold transcriptional response of  Saccharomyces cerevisiae  suggests the need of a proper redox balance. Nevertheless, there are no direct evidence of the links between NAD(P) levels and cold growth and how engineering of enzymatic reactions requiring NAD(P) may be used to modify the performance of industrial strains at low temperature.    Results  Recombinant strains of  S. cerevisiae  modified for increased NADPH- and NADH-dependent Gdh1 and Gdh2 activity were tested for growth at low temperature. A high-copy number of the  GDH2 -encoded glutamate dehydrogenase gene stimulated growth at 15°C, while overexpression of  GDH1  had detrimental effects, a difference likely caused by cofactor preferences. Indeed, neither the Trp −  character of the tested strains, which could affect the synthesis of NAD(P), nor changes in oxidative stress susceptibility by overexpression of  GDH1  and  GDH2  account for the observed phenotypes. However, increased or reduced NADPH availability by knock-out or overexpression of  GRE3 , the NADPH-dependent aldose reductase gene, eliminated or exacerbated the cold-growth defect observed in YEpGDH1 cells. We also demonstrated that decreased capacity of glycerol production impairs growth at 15 but not at 30°C and that 15°C-grown baker’s yeast cells display higher fermentative capacity than those cultivated at 30°C. Thus, increasing NADH oxidation by overexpression of  GDH2  would help to avoid perturbations in the redox metabolism induced by a higher fermentative/oxidative balance at low temperature. Finally, it is shown that overexpression of  GDH2  increases notably the cold growth in the wine yeast strain QA23 in both standard growth medium and synthetic grape must.    Conclusions  Redox constraints limit the growth of  S. cerevisiae  at temperatures below the optimal. An adequate supply of NAD(P) precursors as well as a proper level of reducing equivalents in the form of NADPH are required for cold growth. However, a major limitation is the increased need of oxidation of NADH to NAD +  at low temperature. In this scenario, our results identify the ammonium assimilation pathway as a target for the genetic improvement of cold growth in industrial strains.    Electronic supplementary material  The online version of this article (doi:10.1186/s12934-015-0289-2) contains supplementary material, which is available to authorized users.

microbial cell factories

Redox engineering by ectopic expression of glutamate dehydrogenase genes links NADPH availability and NADH oxidation with cold growth in Saccharomyces cerevisiae