Fermentation of steam pretreated lignocellulosic biomass into acetic acid by Moorella thermoacetica

The current global interest in lignocellulosic biomass has provided momentum and new opportunities in the area of manufacturing biochemicals. One such biochemical, acetic acid, with its broad range of industrial and household applications such as polymers, paints, food and pharmaceuticals has great potential. A systematic study of bioconversion of lignocellulosic sugars to acetic acid by Moorella thermoacetica strain ATCC 39073 was conducted. Five different hydrolysates obtained after steam pretreatment of lignocellulosic biomass were selected. These hydrolysates as well as their corresponding synthetic sugar models were studied in batch fermentations. The bacterial strain (ATCC 39073) can effectively ferment xylose and glucose in steam exploded hydrolysates from switchgrass, forest residues, wheat straw, sugarcane straw and sugarcane bagasse to acetic acid. The highest acetic acid yield obtained was in steam pretreated sugarcane straw hydrolysate with 71% of theoretical yield. In sugarcane straw hydrolysate, consumption of xylose and glucose was faster than their corresponding synthetic sugar model. It was also observed that M. thermoacetica can tolerate process derived inhibitory compounds from steam explosion pretreatment. This strain is capable of fermenting glucose and xylose in the presence of total phenolics up to 3 g/L. Furthermore, this microorganism metabolizes hydroxymethylfurfural and furfural (up to 0.28 and 0.9 g/L, respectively).