Improved transformation of Pseudomonas putida KT2440 by electroporation

Summary An electric field-mediated transformation (i.e. electroporation) was performed to determine optimal conditions for P. putida transformation. The effects of culture age, electroporation buffer composition, electric field strength, pulse time constant and DNA concentration on transformation efficiency were examined. When plasmid DNA of 8 to 11 kb in size was used with an electroporation buffer containing 1 mM HEPES (pH 7.0), maximum transformation efficiency of 1.0 × 10⁷ transformants/g DNA was obtained at field strength of 12 kV/cm with pulse time of 2.5 millisecond. A linear increase in the number of transformants was observed as DNA concentration was increased over 4 orders of magnitude. A linear relationship was observed between growth phase and transformation efficiency up to OD₆₀₀ = 2.0. This reliable and simple method should be useful for introduction of plasmid DNA into intact P. putida cells.