Heat shock-mediated transformation is possible in several Gram-negative bacteria

Transformation of foreign DNA, subjecting Escherichia coli to CaCl₂ treatment followed by heat shock exposure, is a regular approach in recombinant DNA technology. However, in spite of its popularity in E. coli, heat shock transformation is rarely reported in other Gram-negative bacteria. The objective of this research is to demonstrate that the heat shock transformation method can also be performed to introduce genes in different Gram-negative bacteria, such as Ralstonia pseudosolanacearum, Pseudomonas aeruginosa, Pseudomonas putida, and Enterobacter roggenkampii. A green fluorescent plasmid, pDSK-GFPuv, having the size of ~ 8.9 kb, was directly transferred to R. pseudosolanacearum by heat shock at 50 °C for 60s. For P. aeruginosa, P. putida, and E. roggenkampii, the cells were made competent using CaCl_2, followed by heat shock transformation at 50 °C for 180s. As the plasmid contains a gene encoding green fluorescence protein, after successful transformation, bacterial strains were demonstrated for colonization in tomato seedlings. The introduced plasmid was re-isolated from R. pseudosolanacearum to prove its stability inside the bacterium after the heat shock transformation. This easy and convenient method of transformation may be used for other Gram-negative bacteria to prove its wider applicability.