Genetic recombination in Pseudomonas aeruginosa.

SUMMARY: Genetic recombination has been shown to occur in Pseudomonas aeruginosa. Crosses between 18 biochemical mutants of 4 strains were studied and, although non-random segregation was found for non-selective markers, it has not yet been possible to draw conclusions concerning gene order or linkage. The progeny obtained from crosses tended to resemble one parent more than the other. The 4 strains of P. aeruginosa used were interfertile in certain combinations but self-sterile. There was no evidence for an infectious principle affecting fertility but fertility changes may occur amongst recombinant progeny. Genetic studies in Escherichia coli have demonstrated a mechanisni of genetic exchange which until now has been unique among bacteria (see Lederberg et al., 1951; Hayes, 1953). Even within this species practically all of the work has been restricted to the K12 strain. However, Ca\-alli & Heslot (1949) found that the strain NCTC 123 was fertile with K12, but its complex growth requirements made further work difficult. By means of a screening method Lederberg (1951) tested 2000 strains of E. coli and found over 50 to be cross-fertile with K12, and as far as was tested with each other. de Haan (1954) demonstrated recombination in E. coli strain B by transferring the F + character from K12 to E. coli B. This strain had previously been thought to be infertile but is apparently F-. These results suggested that this type of genetic mechanism may occur not only in other strains of E. coli but also in other species of bacteria and for this reason genetic studies were begun with Pseudomonas aeruginosa. This organism grows luxuriantly on the usual bac-teriological media, and grows adequately on a chemically defined medium of glucose and mineral salts. It is of low pathogenicity and can be readily isolated from a variety of sources. METHODS Bacterial strains , 4 collection of strains of Pseudomonas a,eruginosa was obtained, and after studying their general cultural behaviour the following were selected for further investigation. Strain 1, isolated from a wound, Melbourne. This strain freely produces green pigment and grows luxuriantly on nutrient agar. It gives a dense tur-bidity in nutrient broth with a thin surface pellicle and is lysogenic for a bacteriophage which attacks strain L. Strain 3 was isolated from a wound a t Melbourne. It grows readily on nutrient agar forming a scummy growth which does not readily emulsify and in nutrient broth it produces little turbidity …