FIG. 6.
Cell density-dependent degradation of extracellular DNA is a result of the nuclease Dns. Bacterial strains A1552/pBAD-tfoX (parental strain; open bars) and A1552Δdns/pBAD-tfoX (nuclease deletion mutant; filled bars) were rendered competent by artificially inducing tfoX. Samples were taken at the time points indicated on the x axis and checked for their OD600 (secondary y axis) and their frequency of transformation (primary y axis). The results are from three independent experiments. Student's t test results: *, statistically significant difference relative to latest time point at 4:15 (P < 0.05); **, statistically significant difference between early time points (2:15, 2:45, 3:15) and late time points (3:45, 4:15) (P < 0.001).