The recovery of nocardial recombinants from broth cultures

Broth culture media were examined for their ability to support growth and recombination between compatible strains of Nocardia erythropolis. Nutrient(Nut) and peptone-yeast-extract (PY) broths supported the production of recombinants after 36 h of incubation with a maximum recovery of about 6.0 times 10(-7) CFU/ml. Cells mated in trypticase broth (TB) yielded the highest incidence of recombinants (1.0 times 10(-2) CFU/ml) in the absence of parental cell growth. From a chemically defined mating broth (CD), supplemented with limited amounts of the parental-growth requirements, recombinant recovery reached about 1.0 times 10(-4) after 120 h of incubation. The recombinant class types obtained from Nut- or PT-mated strains were predominantly auxotrophic while TB-mated strains produced stable proteotrophs. The high incidence of recombinant types from TB-mated strains was due to growth of selected prototrophic classes. Studies with strains mated in PY broth indicated that the mating event occurs at very low frequencies between older, stationary-phase cells rather than between actively growing, log-phase cells.