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 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 μM Mn²⁺ at 45°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.