Production of ethanol from straw and bamboo pulp by primary isolates of Clostridium thermocellum

Abstract

Clostridium thermocellum strains SS8 and GS1 grew poorly on crude blopolymers but termented them easily after alkall treatment. With 1% alkall-extracted rice straw (AERS) and dellgnified bamboo pulp (DBP), the ethanol-to-substrate (E/S) ratios were almost the same as those obtained when using fillter paper. Increasing the substrate concentrations decreased the percentage substrate degraded and the E/S ratio and concomitantly increased the amount of reducing sugars accumulated. A maximum amount of 8.6 g ethanol/l was produced by strain SS8 out of 37.5 g DBP degraded. Strain GS1 accumulated reducing sugars at substrate concentrations >50 g/l, thereby accounting for about 70% of AERS degraded. This strain produced cellulase on both cellulose and cellobiose. Both the strains grew in the presence of 1.5% (v/v) ethanol. Strain SS8 fermented starch, but the ethanol yield was low compared to that from cellulose. About 75% of starch degraded accumulated as reducing sugars at a substrate concentration of 40 g/l. The Inhibitory effects of ethanol (2 to 4%) were less drastic when growing cultures were challenged than when they were formed in situ. The effect of ethanol depended upon the phase of the culture.