Characterization of Caedibacter endonucleobionts from the macronucleus of Paramecium caudatum and the identification of a mutant with blocked R-body synthesis

Cytology, DNA and host-symbiont relationships of x-like endosymbionts from Paramecium caudatum are described. The symbionts (Caedibacter caryophila, sp. nov.) live in the macronuclei of their hosts. They confer the killer trait upon their hosts and appear well adapted to their endonucleobiotic way of life. R bodies (proteinaceous ribbons associated with killing) are produced, but differ significantly from any of the four R-body classes previously described. C. caryophila and their R bodies were isolated. DNA was extracted from purified symbionts and used to demonstrate that one P. caudatum line harbors a natural mutant which is deficient in R-body production. Melting studies indicate a GC content of 34.6%. No sequence homology between the C. caryophila DNA and the coding sequence for type 51 R-body production was observed. C. caryophila is parasitic, causing the death of its hosts in starving cultures.

Phylogenetic relationships of bacterial endosymbionts of Paramecium aurelia: polynucleotide sequence relationships of 51 kappa and its mutants

Hydroxyapatite chromatographic procedures were used to investigate the deoxyribonucleic acid (DNA) sequence relationships of kappa of Paramecium tetraurelia stock 51 and the organisms that have been designated as mutants of 51 kappa. Of the "mutants" studied, only 51m43 kappa possessed a high percentage (89%) of DNA sequences homologous to those of 51 kappa. All other "mutant" strains possessed less than 25% polynucleotide sequence homology to 51 kappa DNA. The three strains of pi endosymbionts (51m1 pi, 51m43 pi, and 139 pi) share greater than 75% DNA sequence homology with each other and approximately 50% DNA sequence homology with 138 mu, the mate-killer endosymbiont found in P. octaurelia. Only 23% of the 51 kappa DNA sequences were found to be homologous with those of 51m1 kappa. The data indicate that of the "mutants" studied, only 51m43 kappa could be a mutant of 51 kappa. The pi endosymbionts comprise a closely related group of organisms that are also related to 138 mu but not to any of the kappas tested. The group of organisms designated as kappa appears to be comprised of at least two distinct phylogenetic groups.

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

Four variant lines of stock 51 kappa (Paramecium tetraurelia) were screened for the presence of covalently closed circular (CCC) deoxyribonucleic acid (DNA). Stock 51m43 kappa, a nonkiller resistant to 51 killing, contained four classes of CCC DNA: 2.9 X 10(7), 9.7 X 10(7), and 11.8 X 10(7) 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 two CCC species: 0.3 X 10(7) and 4.4 X 10(7) daltons. The buoyant densities of both the chromosomal and CCC DNA were 1.694 to 1.695 g/cm3. Three sizes of CCC DNA were found in 51m1 pi: 0.3 X 10(7), 2.3 X 10(7), and 4.5 X 10(7) daltons. The buoyant densities of both the chromosoaml DNA and the CC DNA were 1.694 to 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 four variant lines, only 51m43 kappa appears to be a mutant of 51 kappa. The chromosomal and CCC DNAs of 51m43 kappa have the same buoyant densities as those of 51 kappa; in addition 51m43 kappa contain a CCC molecule the same size as that found in 51 kappa (2.8 x 10(7) daltons). The three 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.

Covalently closed, circular DNA in kappa endosymbionts of Paramecium

Caedobacter taeniospiralis(kappa), a bacterial endosymbiont isolated fromParamecium tetraureliastock 51, contains, in addition to the bacterial chromosome, covalently closed circular DNA molecules as shown by isolation on dye-buoyant-density gradients. The closed circular molecule has a contour length of 13·75 ± 0·04 µm with a buoyant density of 1·698 g/cm3. The buoyant density of the bacterial chromosome is 1·700–1·701 g/cm3. Kappa of the 51 group isolated from stock 298 and stock 6g2,P. tetraurelia, also contain the closed circular DNA. Two forms of kappa coexist in paramecia: brights and nonbrights. Examination by density-gradient centrifugation of the DNA of brights and nonbrights shows the extrachromosomal DNA to be associated mainly with brights. It is suggested that the extrachromosomal DNA might be the determinant for the refractile bodies and the helical phage-like structures found in brights.

Kappa and other endosymbionts in Paramecium aurelia

Images