Extraction of the Radioresistant Factor of Micrococcus radiodurans

Publisher Website
Google Scholar
Abstract
Extracts of the radioresistant bacterium Micrococcus radiodurans and the relatively sensitive bacterium Sarcina lutea were prepared giving an ultrafiltrate of molecular weight less than 15,000. The protective action of these extracts against 200 KVP X-rays was tested by/determining survival curves of Escherichia coli B/r suspended in them. The survival curve in M. radiodurans extract is always greater than in buffer, whereas S. lutea extract produces a survival curve below that of buffer suspended cells. The influence of dilution of the extracts on survival was determined at 40 kr. M. radiodurans extract protects at high concentration to the 2% level, dropping to 0.6% survival at 64X diluting to the buffer value of 1% at lower concentrations.S. lutea extract sensitizes at all dilutions, increasing with concentration. Autoclaving increases the protective action of the M. radiodurans extract to 10% survival, but does not influence the response of the S. lutea extract. This probably represents disulfide to sulfhydryl conversion. By comparison with the concentration effect of [beta]-mercaptoethylamine (MEA), the amount of protective agent present in the M. radiodurans cell extract is equivalent to 4 to 10 m[image] of added MEA. This level is sufficient to confer the observed radioresistance of M. radiodurans. The survival curves of M. radiodurans and S. lutea are modified both in shoulder and slope in the presence of MEA, as is necessary for this mechanism of radioresistance.