[Simple method for determining cellulolytic activity in fungi]

Wild fungal strains isolated from litter and soil were inoculated in test tubes containing a synthetic medium with 0.5% sodium carboxymethylcellulose (CMC) as sole carbon source. After the incubation time, cylindrical probes were taken from each tube using a borer and stained with Congo red 0.1% to reveal the remaining CMC. The relative cellulase activity was estimated by measuring the deepness of the clearing zone, and the growth by the limit of mycelial penetration in the medium. The ratio: hydrolysis zone/depth of growth, provides additional information to compare strains. A test using culture supernatants of liquid media growing strains was developed for enzyme assay using a modification of the cylinder-plate method. Petri dishes were filled with agar-CMC medium and cups were cut off with a steel punch. Such cups were filled with culture supernatants. After incubation, the plated were stained with Congo red, and the diameter of each cleared zone was recorded. Comparative studies of strains could be performed as well as quantitation of enzyme activity using a standard cellulase solution and computing the area of the cleared zones. This method may be useful when a large number of strains must be tested for cellulolytic activity or when conventional tests fail for assaying enzymatic induction in vitro.