Copyright © 1991, American Society for Microbiology Transformation of Freshwater and Marine Caulobacters

We performed plasmid electrotransformation of Caulobacter crescentus strains and obtained up to 3 x 108 transformants per,ug of pKT230. The presence and integrity of the paracrystalline protein surface (S) layer influenced electroporation; caulobacters lacking the S layer were electrotransformed 10 times more efficiently than caulobacters possessing the S layers. A procedure yielding 1,500 transformants per,ug of pKT230 was developed for a marine caulobacter. Electroporation was used in combination with several genetic techniques, including introduction of ligation mixtures, suicide transposon mutagenesis, gene replacement, and plasmid electrotransfer from Escherichia coli to caulobacters. Caulobacters, particularly strains of Caulobacter cres-centus, have been the subject of genetic analysis for years; however, the lack of a transformation method has meant that introduction ofDNA has been possible only via conjugation and phage transduction (7, 8). Conjugation is relatively inefficient and awkward, requiring conjugation-proficient strains and selection procedures, often with several antibi-otics and viruses directed against donor cells. Therefore we investigated electrotransformation (electroporation) for its potential to transform caulobacters. We also investigated the utility of electrotransformation in improving several genetic techniques. Most published work on the electrotransformation of bacteria reports the use of equipment capable of maximum field strengths of 6.25 kV/cm and has demonstrated transfor