Butyric acid fermentation from pretreated and hydrolysed wheat straw by an adapted Clostridium tyrobutyricum strain

Butyric acid is a valuable building-block for the production of chemicals and materials and nowadays it is produced exclusively from petroleum. The aim of this study was to develop a suitable and robust strain of Clostridium tyrobutyricum that produces butyric acid at a high yield and selectivity from lignocellulosic biomasses. Pretreated (by wet explosion) and enzymatically hydrolysed wheat straw (PHWS), rich in C6 and C5 sugars (71.6 and 55.4gl^-1 of glucose and xylose respectively), was used as substrate. After one year of serial selections, an adapted strain of C.tyrobutyricum was developed. The adapted strain was able to grow in 80% (vv^-1) PHWS without addition of yeast extract compared with an initial tolerance to less than 10% PHWS and was able to ferment both glucose and xylose. It is noticeable that the adapted C.tyrobutyricum strain was characterized by a high yield and selectivity to butyric acid. Specifically, the butyric acid yield at 60-80% PHWS lie between 0.37 and 0.46gg^-1 of sugar, while the selectivity for butyric acid was as high as 0.9-1.0gg^-1 of acid. Moreover, the strain exhibited a robust response in regards to growth and product profile at pH 6 and 7.