Purification of a thermostable endochitinase from Streptomyces RC1071 isolated from a cerrado soil and its antagonism against phytopathogenic fungi

Aims: The chitinolytic activity of an actinomycete, isolated from a tropical acidic ferrasol (FAO) under cerrado (savanna) vegetation, is reported. Methods and Results: Selection of the strain was based on spot inoculation on solid colloidal chitin medium. The use of chemotaxonomic, morphological and physiological procedures placed it in the Streptomyces genus, but identification to species level could not be achieved. A protein with endochitinase activity was isolated and purified from the supernatant fluid by concentration, precipitation, hydrophobic interaction, gel filtration and adsorption procedures. The molecular size of the purified chitinase was estimated by gel filtration to be 70 kDa, and its pI was 6.1. The enzyme had temperature and pH optima of 40 degreesC and 8.0, respectively, and showed thermal (30-70 degreesC) and pH (4-9) stabilities. Antifungal activity of the selected strain was observed following in vitro experiments using growing cells, crude extract or the purified endochitinase, and by detecting growth inhibition of the tested phytopathogenic fungi. Conclusions: Strain Streptomyces RC 1071 could not be placed into any known species, suggesting a new taxon. The purified endochitinase presented similar molecular weight, optimum temperature and pH activity, and stability of other endochitinolytic enzymes reported in the literature. In all three in vitro experiments performed, inhibition of growth of the phytopathogenic fungi used as test organisms was observed. Significance and Impact of the Study: Some of the endochitinase characteristics such as thermal stability, as well as pH tolerance, are very interesting for biotechnological purposes. In addition, due to its antifungal activity, Streptomyces RC 1071 seems promising for use in biological control.