Co-fermentation of mixed sugars to produce butanol is an attractive route in sucrochemical production chains. Herein, high-level mixed sugars from sugarcane bagasse hemicellulosic hydrolysate (HH) and molasses (SCM) were investigated as potential substrates for acetone-butanol-ethanol (ABE) production in batch fermentation by Clostridium saccharoperbutylacetonicum DSM 14923. HH produced after hydrothermal pretreatment was concentrated 5-fold and was called concentrated hemicellulosic hydrolysate (CHH). The fermentation media that were investigated consisted solely of CHH and SCM and three CHH-to-SCM ratios were used to provide 30 g/L initial sugar concentrations and furan derivatives lower than 0.1 g/L. For CHH50/SCM50 and CHH75/SCM25, diluting CHH to concentrations of 15 g/L sugars and 22.5 g/L sugars, respectively, which were supplemented with SCM and nutrients, suffered growth inhibition as a function of the concentration of undissociated acid in the medium. The best-performing medium, CHH25/SCM75 (7.5 g/L and 22.5 g/L sugars from CHH and SCM, respectively and about 0.017 g/L furan derivatives), showed 97 % sugar consumption, and in the pH range of 5.5–6.5, undissociated acetic acid was not an inhibitory molecular form to C. saccharoperbutylacetonicum. After 30 h of fermentation, 7.8 and 9.8 g/L butanol and ABE were produced, respectively, which yielded 0.28 and 0.36 g/g. Based on our findings, C. saccharoperbutylacetonicum exhibits its potential and effective application for renewable butanol production by co-fermenting mixed sugars.

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.