Bioconversion process of rice straw by thermotolerant cellulolytic Streptomyces viridiochromogenes under solid-state fermentation conditions for bioethanol production

Enzymatic hydrolysis of the cellulose fraction of rice straw to glucose using solid-state fermentation for bioethanol production is a focus of current attention. A total of 10 actinomycetes isolates were isolated from soils and decayed rice straw. All these isolates were purified and screened for their cellulolytic activity; one strain was selected for further study and identified as Streptomyces viridiochromogenes . Optimization of fermentation conditions showed highest cellulolytic enzymes production on the 5th day at pH 6.5 and at 40°C. The production of enzymes reached its maximal value at 4.0 g of rice straw/250 ml flask. Avicelase and total cellulase productivity were highly increased by the addition of NH 4 Cl as Nsource, while maximum activity of CMCase was recorded by the addition of peptone as N-source to the fermentation medium. The influence of various physico-chemical factors on enzyme activity was also investigated. The half life time of avicelase, total cellulase and CMCase at 60°C was 39.4, 50.0 and 78.58 min, respectively. A maximum of ethanol production 1.428±0.074% (v/v) by Saccharomyces cereviseae using dilute acid pretreated rice straw hydrolysate with initial soluble sugar 2.340±0.072%  was recorded after 2 days of fermentation. Key words : Bioethanol, cellulolytic enzymes, rice straw, solid-state fermentation, Streptomycesviridiochromogenes.