Studies of Extracellular and Intracellular Bacterial Deoxyribonucleic Acids

Abstract

Highly polymerized bacterial deoxyribonucleic acids (DNAs) obtained from extracellular and from intracellular locations were analysed. DNAs from two strains (Staphylococcus aureus and S. epidermidis) were of the type having high adenine and thymine contents; two others (Alcaligenes faecalis and Pseudomonas fluorescens) had a high content of guanine and cytosine. For each micro-organism the composition of extracellular DNA was essentially the same as that of the intracellular DNA. Conditions associated with the extracellular accumulation of DNA in cultures of 3 strains were investigated. S. aureus elaborated a deoxyribonuclease (DNase) which required calcium ion and high pH for activity. In a culture medium of c. pH 6 and insufficient calcium, the DNase was inactive and DNA slime accumulated. In cultures of P. fluorescens a specific ribonuclease-sensitive DNase inhibitor protected slime DNA from depolymerization by culture DNase. In cultures of A. faecalis, also, both a DNA slime and a low concentration of DNase may occur. This enzyme, detected by studying its action against solutions of calf thymus DNA prepared from dried fibres, was activated by various cations within the pH range of cultures. Unlike other DNases, however, it has little capacity to attack the slime-layer DNA, which presumably is more nearly native.