Butyric acid fermentation from pre-treated wheat straw by a mutant clostridium tyrobutyricum strain

Only little research on butyric acid fermentation has been carried out in relationship to bio-refinery perspectives involving strain selection, development of adapted strains, physiological analyses for higher yield, productivity and selectivity. However, a major step towards the development of a sustainable industrial society is a shift from petroleum-based resources to the use of renewable resources. An ongoing effort is focused on developing bio-refineries as an alternative way of producing fuels and chemical building-blocks from renewable resources. Thus, today’s organic waste may become tomorrow’s platform for a variety of products for industrial use. Butyric acid is considered as a potential chemical building-block for the production of chemicals for e.g. polymeric compounds and the aim of this work was to develop a suitable and robust strain of Clostridium tyrobutyricum that produces less acetic acid (higher selectivity), has a higher yield and a higher productivity of butyric acid from pre-treated lignocellulosic biomass. Pre-treated wheat straw was used as the main carbon source. After one year of serial adaptation and selection a mutant strain of C. tyrobutyricum was developed. This new strain could grow in up to 80% pre-treated wheat straw and can ferment both glucose and xylose. The yield of butyric acid without optimization was 0,37±0,051 g butyric acid/g sugar monomers and the acetate yield was 0,06±0,021 g acetic acid/g sugar monomers. Moreover, the strain could grow without addition of yeast extract. Further optimization of yield and productivity is under investigation.