Purification and properties of a β-1,6-glucanase from Streptomyces sp. EF-14, an actinomycete antagonistic to Phytophthora spp.

Extracellular enzymes with glucanase activities are an important component of actinomycete-fungus antagonism. Streptomyces sp. EF-14 has been previously identified as one of the most potent antagonists of Phytophthora spp. A β-1,6-glucanase (EC 3.2.1.75; glucan endo-1,6-β-glucosidase) was purified by four chromatographic steps from the culture supernatant of strain EF-14 grown on a medium with lyophilized cells of Candida utilis as main nutrient source. The glucanase level in this medium followed a characteristic pattern in which the rise of β-1,6-glucanase activity always preceded that of β-1,3-glucanase. The molecular mass of the enzyme was estimated to be 65 kDa and the pI approximately 5.5. It hydrolyzed pustulan by an endo-mechanism generating gentiobiose and glucose as final products. Laminarin was not hydrolyzed indicating that the enzyme does not recognize β-1,6-links flanked by β-1,3-links. No significant clearing of yeast cell walls in liquid suspensions or in agar plates was observed indicating that this β-1,6-glucanase is a non-lytic enzyme. This is the first β-1,6-glucanase characterized from an actinomycete.