Extracellular deoxyribonuclease production by a thermophile, Streptomyces thermonitrificans

A thermophilic bacterial strain, Streptomyces thermonitrificans, produced high levels of extracellular deoxyribonuclease (DNase) when grown on NBG medium (containing 1% peptone, 0.3% beef extract, 1% glucose and 0.5% NaCl). Maximum DNase activity (140 U x ml(-1)) was obtained, in 24 h, when the culture was grown on modified NBG medium (containing 1.3% beef extract, 1% glucose, 0.5% NaCl and 50 microM Mn2+ at 45 degrees C. The crude enzyme showed higher activity on native DNA than on sonicated and heat denatured DNA. Moreover, addition of Mn2+ in the assay mixture resulted in a significant stimulation (10-15 fold) of the enzyme activity.