*4.3. Qualitative Evaluation of Enzyme Activities of Actinobacterial Strains*

Of the 60 strains analyzed in vitro (4.2), the 31 most effective were selected to determine their chitinolytic, cellulolytic, proteolytic activity (Table 6). For chitinolytic activity, all the strains were grown on Colloidal Chitin Agar culture medium (pH = 7) at 28 ◦C for seven days in darkness [40]. For cellulolytic activity, the strains were grown on ISP2 (International Streptomyces Project) [41] with cellulose (1%, *w*/*v*) (pH = 7.2) also at 28 ◦C for seven days in darkness; then a congo red solution (1%) was added as developer for 15 min; and finally, the congo red solution was removed and NaCl solution (1 M) was added for 15 min [42]. For proteolytic activity, the strains were grown on ISP2 with 1% skimmed milk at 30 ◦C for seven days in darkness [43]. For each parameter evaluated, there were three replicated Petri dishes per strain in a completely randomized design (93 Petri dishes in total), and the experiment was performed three times under similar conditions.

In all cases, after seven days of incubation, the halo surrounding the colonies of the actinobacterial strains was measured (mm) from the center of the inoculated mycelial disc.
