Agradecimentos: We thank Prof. Dr. Walter van Gulik from Delft University of Technology for his useful comments and language revision, and the Brazilian Center for Research in Energy and Materials (CNPEM) for providing access to the bioprocessing facility of the Brazilian Bioethanol Science and Technology Laboratory (CTBE) Ver menos

Robust strains are essential towards success of n-butanol production from lignocellulosic feedstock. To find a suitable strain to convert a non-detoxified hemicellulosic hydrolysate of sugarcane bagasse, we first assessed the performance of four wild-type butanol-producing Clostridium strains (C. acetobutylicum DSM 6228, C. beijerinckii DSM 6422, C. saccharobutylicum DSM 13864, and C. saccharoperbutylacetonicum DSM 14923) in batch fermentations containing either xylose or glucose at 30 g L-1 as sole carbon sources. C. saccharoperbutylacetonicum was selected after achieving butanol yields as high as 0.31 g g(-1) on glucose and 0.25 g g(-1) on xylose. In a 48-h fermentation containing a mixture of sugars (93% xylose and 7% glucose) that mimicked the hydrolysate, C. saccharoperbutylacetonicum delivered the highest butanol concentration (14.5 g L-1) when the initial sugar concentration was 50 g L-1. Moreover, the selected strain achieved the highest butanol yield (0.29 g g(-1)) on xylose-rich media reported so far. Meanwhile, C. saccharoperbutylacetonicum produced 5.8 g butanol L-1 (0.22 g g(-1) butanol yield) when fermenting a non-detoxified sugarcane bagasse hemicellulosic hydrolysate enriched with xylose (30 g total sugars L-1). Although sugars were not exhausted (4.7 g residual sugars L-1) even after 72 h because of the presence of lignocellulose-derived microbial inhibitors, these results show that C. saccharoperbutylacetonicum is a robust wild-type strain. This microorganism with high butanol tolerance and yield on xylose can, therefore, serve as the basis for the development of improved biocatalysts for production of butanol from non-detoxified sugarcane bagasse hemicellulosic hydrolysate Ver menos