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Background  Decarboxylation of α-ketoisovalerate to isobutyraldehyde is a key reaction in metabolic engineering of  Saccharomyces cerevisiae  for isobutanol production with published studies relying on overexpression of either the native  ARO10  gene or of the  Lactococcus lactis kivD  decarboxylase gene resulting in low enzymatic activities. Here, we compare relevant properties for isobutanol production of Aro10, KivD and an additional, less studied,  L. lactis  decarboxylase KdcA.    Results  To eliminate interference by native decarboxylases, each 2-oxo acid decarboxylase was overexpressed in a ‘decarboxylase-negative’ ( pdc1 Δ  pdc5 Δ  pdc6 Δ  aro10 Δ)  S. cerevisiae  background. Kinetic analyses in cell extracts revealed a superior  V  max / K  m  ratio of KdcA for α-ketoisovalerate and a wide range of linear and branched-chain 2-oxo acids. However, KdcA also showed the highest activity with pyruvate which, in engineered strains, can contribute to formation of ethanol as a by-product. Removal of native decarboxylase genes eliminated growth on valine as sole nitrogen source and subsequent complementation of this growth impairment by expression of each decarboxylase indicated that based on the increased growth rate, the in vivo activity of KdcA with α-ketoisovalerate was higher than that of KivD and Aro10. Moreover, during oxygen-limited incubation in the presence of glucose, strains expressing  kdcA  or  kivD  showed a ca. twofold higher in vivo rate of conversion of α-ketoisovalerate into isobutanol than an  ARO10 -expressing strain. Finally, cell extracts from cultures grown on different nitrogen sources revealed increased activity of constitutively expressed KdcA after growth on both valine and phenylalanine, while KivD and Aro10 activity was only increased after growth on phenylalanine suggesting a difference in the regulation of these enzymes.    Conclusions  This study illustrates important differences in substrate specificity, enzyme kinetics and functional expression between different decarboxylases in the context of isobutanol production and identifies KdcA as a promising alternative decarboxylase not only for isobutanol production but also for other branched-chain and linear alcohols.    Electronic supplementary material  The online version of this article (doi:10.1186/s13068-015-0374-0) contains supplementary material, which is available to authorized users.

Comparative assessment of native and heterologous 2-oxo acid decarboxylases for application in isobutanol production by Saccharomyces cerevisiae