Recombination in Bact. coil K 12: Unidirectional Transfer of Genetic Material

Abstract

THE development of nutritionally independent prototroph colonies from mixed cultures of doubly dependent mutant strains of Bact. coli K 12 was first demonstrated in 1946¹. Back mutation to prototrophism did not occur when the mutants were cultured separately. Since the pattern of unselected marker characters in prototrophs was usually different from that in either mutant, the phenomenon was clearly due to genetic recombination. The incompetence in recombination of culture filtrates (unlike type transformation in Pneumococcus), and recent evidence for the occasional occurrence of diploid heterozygous prototrophs², strongly support the current theory that the genetic transfer is mediated by sexual conjugation. Attempts to reproduce the phenomenon in other strains and species have failed, though successful out-crossing of K 12 mutants with a strain of Bact. acidi lactici has been reported³.