A BIOLOGICAL ASSAY FOR THE SENSITIVE AND QUANTIFIABLE DETECTION OF EXTRACELLULAR MICROBIAL DNASES

Natural genetic transformation is a process by which a recipient cell in the physiological state of competence is able to take up DNA, to integrate one strand into the chromosome and to express a new trait. A sensitive and quantifiable assay for DNase activity was developed which relies on the inactivation of the transforming activity of DNA during cocultivation on the surface of agar medium of the naturally transformable recipient, Pseudomonas stutzeri, with transforming DNA and microorganisms to be tested for DNase production. The performance of this assay was compared to that of two different qualitative DNA agar colorimetric tests for DNases in the examination of 22 strains of 7 Gram-positive and Gramnegative bacterial species and fresh soil isolates as well as two yeast species. By the transformation assay low and high extracellular DNase activities were quantifiable including cell surface-associated DNase which was not detectable by the conventional agar colorimetric DNase assays.