Abstract

Cellulase is a very important enzyme due to its great industrial applications. Six marine strains of actinomycetes were screened for their carboxymethyl cellulase (CMCase) productivity. Streptomyces ruber was chosen to be the best producing strain. The highest enzyme production (25.6 U/ml) was detected at pH 6 and 40°C after 7 days of incubation. Plackett-Burman design was applied to optimize the different culture conditions affecting enzyme production. Results showed that a high concentration of KH₂PO₄, and a low concentration of MgSO₄ had a significant effect on enzyme production. Rice straw was used as a low cost source of cellulose. It was found that 30 g/l rice straw was the suitable concentration for maximum enzyme production. Partial purification of cellulase enzyme using an anion-exchange chromatography resulted in the detection of two different types of CMCases, type I and II, with specific activity of 4239.697 and 846.752 U/mg, respectively. Moreover, estimation of their molecular weight revealed 27.0 kDa for cellulase type I and 24.0 kDa for cellulase type II. It could be concluded that S. ruberis a powerful cellulase producer strain under our tested experimental conditions.

Key words: Cellulase production, Streptomyces ruber, Plackett-Burman design, rice straw, enzyme characterization.

Abbreviation

CMC, Carboxymethyl cellulose; CMCase, carboxymethyl-cellulase; DNS, dinitrosalicylic acid; DEAE, diethylaminoethyl.