Variation in density and transformation potential in deoxyribonucleic acid from Neisseria meningitidis.

Jyssum, Kaare (University of Oslo, Oslo, Norway), and Sidsel Jyssum. Variation in density and transformation potential in deoxyribonucleic acid from Neisseria meningitidis. J. Bacteriol. 90:1513-1519. 1965.-Three variants of Neisseria meningitidis have been examined with regard to competence. One is the genetically competent M1-12 his(-)cp(+), the second is the genetically incompetent M1-12 his(-)cp(-) which does not revert to competence, and the third is the incompetent mutant M1-18 his(-)gly(-)(cp) which reverts to competence. An examination of the relation between the deoxyribonucleic acid (DNA) and protein contents indicates the existence of more DNA in strain M1-12 his(-)cp(+) than in strain M1-12 his(-)cp(-). DNA prepared from the three strains was examined by density gradient centrifugation. The distribution of DNA in the gradients was unimodal. No significant differences could be observed between the distribution curves obtained from the three test strains. When the distribution in the gradients of transformation potential corresponding to five biochemical markers was measured, a pronounced difference was found among the three test strains. The distribution of the markers in the gradient from strain M1-12 his(-)cp(-) was unimodal. In the DNA from strain M1-18 his(-)gly(-)(cp), all the markers examined showed bipartite distribution curves with low relative specific transforming activity, corresponding to an area near the middle of the DNA distribution. The strain M1-12 his(-)cp(+) showed a similar bipartite distribution of four biochemical markers, whereas the marker pro had a very high relative specific transforming activity in the area where the other markers tested had a reduced activity. The nature of the DNA with reduced transformation potential which seems to be present in strains M1-12 his(-)cp(+) and M1-18 his(-)gly(-)(cp) is discussed in relation to previous observations. The possibility has been presented that the cp factor in N. meningitidis may be a true episome.