Chitinase, chitosanase, and antifungal activities from thermophilic streptomycetes isolated from compost

The Streptomyces genus comprises a large and diversegroup of bacteria, many of which are commercially exploited forthe production of antibiotics and lytic enzymes. The thermophilicspecies are less studied than the predominant mesophilic species.However, the first ones are a potential source of thermostable bioactiveproducts and enzymes with novel properties. In this study, twoselected thermophilic streptomycetes were identified and their chitinolyticactivities were evaluated. The identification of these two isolateswas performed by microscopic morphology, partial 16S rDNAsequences, and its phylogenetic analysis. To study the chitinolyticactivities of these isolates, the effects of colloidal chitin (CC) andfungal cell walls (FCW) on the chitinase activities and chitinase andchitosanase isoform patterns were determined. Additionally, in vitroconfrontations against chitinolytic phytopathogenic fungi wereperformed at 45 °C and 65 °C. Both isolates (AC4 y AC7) wereidentified as members of the streptomycete thermophilic clade. Thehighest chitinolytic activities were observed in the combinations0.1% FCW/0.1% CC and 0.1% FCW/0.3% CC with maximum valuesof 0.7 U/μg and 0.45 U/μg, respectively for the AC4 strain, andwith values of 0.48 U/μg in both treatments for the AC7 strain. Theelectrophoretic profiles of chitinase and chitosanase activity showednot only differences in bands intensity, but also few new bands wereobserved. Both isolates inhibited the growth of Rhizoctonia solaniand Fusarium oxysporum. The present study shows that thermophilicstreptomycetes have potential bioactivities that might be exploitedin horticulture.