RESUMO
Matings of genetically marked derivatives of Mycoplasma pulmonis resulted in the exchange of chromosomal DNA and the appearance of doubly marked transconjugants. Transposons Tn916 and Tn4001, and a series of integrative plasmids derived from their cloned antibiotic resistance genes, were used to construct antibiotic-resistant mycoplasmal derivatives to examine this phenomenon at the molecular level. Genetic exchange occurred on agar surfaces at frequencies ranging from 3.3 X 10(-4) to 6.4 X 10(-8) transconjugants per CFU. Examination of chromosomal DNA from transconjugants by hybridization revealed that the transposons or integrated plasmids were in the same chromosomal locations as in the parental strains, indicating that exchange involved the transfer of chromosomal DNA and homologous recombination. Transfer was not affected by DNase, polyethylene glycol, EDTA, or calcium chloride but was affected by treatment of either parent with trypsin. Mixing of mating strains before plating had no effect on mating frequencies, but mating did occur in liquid media. The ability to exchange chromosomal markers was limited to selected strains of M. pulmonis; mating did not occur with Acholeplasma laidlawii or M. gallisepticum. Heat and UV inactivation studies revealed that nonviable cells could act as donors in matings. The evidence presented supports a conjugationlike mechanism involving specific trypsin-sensitive membrane components.
Assuntos
Conjugação Genética , Elementos de DNA Transponíveis , Escherichia coli/genética , Mycoplasma/genética , Plasmídeos , Transformação Bacteriana , Acholeplasma laidlawii/genética , Cromossomos Bacterianos , Conjugação Genética/efeitos da radiação , Cruzamentos Genéticos , DNA Bacteriano/genética , Mycoplasma/efeitos da radiação , Transformação Bacteriana/efeitos da radiação , Raios UltravioletaRESUMO
Gossypol was found to be an effective male contraceptive. The most serious side effect of gossypol contraception was the presumed lowering of serum potassium levels. The purpose of this present randomized and controlled study was to evaluate the merit of ingesting K salt or a potassium blocker while using gossypol. Results indicated that supplementation of K salt does not cause a reversal of the effect of gossypol on serum potassium levels and the blocker triamterene does not prevent loss of serum potassium.
