Stable transformation of Chromobacterium violaceum with a broad-host-range plasmid

Stable transformants of Chromobacterium violaceum were obtained by high-voltage electroporation with a 7-kilobase binary plasmid. The technique was reliable, reproducible, and simple, with efficiencies of 10⁵ transformants/μg of plasmid DNA. The electrical conditions that resulted in the highest efficiencies were short pulse length (4.4–4.5 ms) and high voltage (12.5 kV/cm). The numbers of transformants were almost the same during the growth exponential phase (variation at optical density) and resulted in the highest efficiencies at DNA concentration of 250 pg/ml. Saturation appeared to begin at 4 μg/ml of DNA. This method of C. violaceum transformation should enhance the genetic and biotechnological research by providing a valuable, widely used procedure of introducing DNA into this bacterium.