DNase-resistant DNA in the extracellular and cell wall-associated fractions of Frankia strains R43 and CcI3

DNases were shown to be present in the extracellular fraction of Frankia st rains R43 and CcI3. In spite of this, DNA was found in both the extracellul ar and cell wall fractions of these strains, and it was shown that extracel lular DNA was resistant to the DNases secreted into the culture medium of b oth Frankia strains. Furthermore, Southern blot analysis under high stringe ncy conditions revealed the chromosomal origin of the cell wall-adsorbed DN A (CW-DNA). Mobility gel band shift assays suggested that the extracellular DNA and the CW-DNA are engaged in complexes with other molecules, most lik ely proteins, which are probably responsible for the enzymatic resistance o bserved against extracellular DNase activities. In addition, it was shown t hat lysis of a small proportion of the cells in the exponential growth phas e may account for the DNA being released into the supernatant and adsorbed to the cell wall.