CHARACTERIZATION OF AN ACTIVITY FROM THE STRICT ANAEROBE ROSEBURIA-CECICOLA THAT DEGRADES DNA WHEN EXPOSED TO AIR

Roseburia cecicola is an obligately anaerobic bacterium that is extrem ely sensitive to oxygen. Genomic DNA isolated from cells exposed to ai r for even a brief period (<5 min) is partially degraded, while DNA ex tracted from cells maintained in an anaerobic environment remains inta ct. Cells exposed to air for longer and longer periods yield DNA which is progressively degraded into fragments with decreasing sizes. Oxyge n toxicity for this anaerobe appears to result, at least in part, from degradation of its genomic DNA. Cell lysates of the organism exhibite d a similar ability to degrade exogenous sources of DNA when assayed i n vitro under aerobic conditions. A substance that degrades both DNA a nd RNA when incubated aerobically was partially purified from such lys ates. It has an approximate molecular weight of 2,800 and is unlikely to be a protein. It requires a reducing agent for activity and can be inhibited by catalase and peroxidase but not superoxide dismutase. The rate at which it degrades DNA in vitro can be enhanced by temperature s above 37-degrees-C or by oxygen at partial pressures above atmospher ic pressure. These results suggest that this substance degrades nuclei c acids by a mechanism involving oxygen radicals.