Factors affecting quantitative transformation of streptomycin resistance markers in Acinetobacter calcoaceticus.

Quantitative transformation of Acinetobacter calcoaceticus BD4-Ss exposed to autologous DNA in a liquid system was examined with streptomycin resistance as a marker. The exposure to DNA was terminated by addition of DNase at set intervals. The variables tested were concentrations of autologous Sr-DNA, exposure time, growth phase, recipient cell density, and the pH of the liquid transformation system. The ratio of transformants to total number of recipient cells (T/R-ratio) was proportional to the DNA concentration up to a level of about 10 micrograms/ml. There was a constant increase of transformant numbers upon time of exposure. The T/R ratio was highest at the early growth phase, but the total number of transformed cells per ml culture aliquot was only raised by a factor approximately 10 from the earlier to the later growth phases and non increase was observed in recipients grown for more than 3 hours. There was a marked relationship between the relative number of transformants per total number of recipients in that the T/R-ratio was markedly higher with fewer cells per ml in the transformation broth system where exposure to DNA occurred. The transformation was higher at a pH of 7.3 than 7.0. The results enabled definition of the optimal test system for quantitative transformation of A. calcoaceticus with the strain BD4 as recipient.