Chromosomal and extrachromosomal deoxyribonucleic acid from four bacterial endosymbionts derived from stock 51 of Paramecium tetraurelia

Abstract

Four variant lines of stock 51 kappa (P. tetraurelia) were screened for the presence of covalently closed circular (CCC) DNA. Stock 51m43 kappa, a nonkiller resistant to 51 killing, contained 4 classes of CCC DNA: 2.9 .times. 107, 5.9 .times. 107, 9.7 .times. 107 and 11.8 .times. 107 daltons. The buoyant densities of 51m43 kappa chromosomal and CCC DNA were 1.700 and 1.698 g/cm3, respectively. Stock 51m43 pi, a sensitive nonkiller, contained 2 CCC species: 0.3 .times. 107 and 4.4 .times. 107 daltons. The buoyant densities of the chromosomal and CCC DNA were 1.694-1.695 g/cm3. Three sizes of CCC DNA were found in 51m1 pi: 0.3 .times. 107, 2.3 .times. 107 and 4.5 .times. 107 daltons. The buoyant densities of both the chromosomal DNA and the CCC DNA were 1.694-1.695 g/cm3. It is not known whether 51m1 kappa, a sensitive spinner killer, contains CCC DNA. The buoyant density of its chromosomal DNA was 1.703 g/cm3. Of the 4 variant lines, only 51m43 kappa appears to be a mutant of 51 kappa. The chromosomal and CCC DNA of 51m43 kappa have the same buoyant densities as those of 51 kappa; 51m43 kappa contain a CCC molecule the same size as that found in 51 kappa (2.8 .times. 107 daltons). The 3 other lines are probably bacterial species that are distinct from 51 kappa and which, at one time, were co-inhabitants with 51 kappa in stock 51 paramecia.