초록
Among four isolated cellulolytic microorganisms, Streptomyces sp. MDS can utilize a broad range of cellulosic substrates including: carboxymethyl cellulose, avicel, xylan, cellobiose, filter paper, wood straw and rice straw by producing a large amount of endoglucanase, exoglucanase, cellobiase, xylanase and glucoamylase. Effects of different physicochemical parameters to achieve maximum production of cellulolytic enzymes were systematically investigated. It was found that the cellulolytic enzyme activities were mainly located at extracellular location. It was observed that supplementation of CaCl<SUB>2</SUB> (5 mM) as a metal additive significantly induced the whole enzyme system. These cellulases also have high thermal stability as evidenced by retaining 60-70% activity at 90 <SUP>o</SUP>C and pH 5 and alkalotolerance as more than 55-60% of the activity at pH 10 and 40 <SUP>o</SUP>C and 60 <SUP>o</SUP>C (for endoglucanase) after 1 h of incubation. The enzymes also retained up to 50-70% of its initial activity upon incubation in the presence of commercials detergents for 1 h. Finally, the efficiency of fermentative conversion of the CMC and rice straw hydrolyzate by Saccharomyces cerevisiae (KCTC 7296) resulted in 55.8 and 57.2% of maximum theoretical ethanol yield based on sugar (glucose and xylose) fermentation, respectively.