Carboxymethyl cellulose (CMC)-degrading ability of Rhizopus azygosporus UICC 539 at various temperatures

Abstract

Carboxymethyl cellulase (CMC) is an excellent substrate for endocellulases. Most cellulases are endocellulases and some aerobic fungi produce these enzymes. Many hydrolase enzymes including cellulases are already used commercially in industry. However, there is still an increasing need for the new enzymes. i.e. the enzyme biocatalysts that can withstand conditions such as high temperatures and high substrate concentrations. This study was carried out to detect CMC-degrading ability of Rhizopus azygosporus UICC 539 on 1 % (w/v) and 2 % (w/v) carboxymethyl cellulose (CMC) at various temperatures. Agar block (diameter 6 mm) containing a concentration of R. azygosporus cells at approximately 106 cell/mL was prepared from a 5-day old fungus in Potato Sucrose Agar (PSA) at 30 °C. The agar block was inoculated on modified Czapek’s Dox Agar (CDA) plates in the absence of a carbon source, and 1 % (w/v) or 2 % (w/v) CMC was appended as a sole carbon source. The CDA plates were incubated for 3 days and 5 days at different temperatures (30 °C, 35 °C, 40 °C, 45 °C and 50 °C). The modified CDA plates without the fungus served as control. Clear zones were indicative of CMC hydrolysis and Congo red was used as an indicator. The following formula was employed to calculate the Enzymatic Index (EI): R/r, where R was the diameter of the entire clear zone, and r was the diameter of the fungal colony. The results showed that CMC-degrading ability of R. azygosporus UICC 539 was detected at both CMC concentrations and at all tested temperatures. High EI was observed at 50 °C in both concentrations of CMC, with the highest EI at 1 % CMC after day-5 of incubation. In conclusion, R. azygosporus UICC 539 was able to degrade 1 % and 2 % carboxymethyl cellulose in the temperature range of 30–50 °C and produced clear zones, which was indicative that this strain secreted CMCase (endoglucanase) into the medium. R. azygosporus UICC 539 was a potential candidate for high temperature conditions which is required in hydrolyzing cellulose-containing agricultural byproducts.