Effective transformation of the cyanobacterium Spirulina platensis using electroporation

Although Spirulina (Arthrospira) is expected to be a suitable organism for producing recombinant proteins, a gene transfer system has not yet been est ablished, due to a lack of suitable vectors and because Spirulina appears r efractory to common genetic manipulations. As the initial stages of the dev elopment of recombinant DNA methodology, we examined the effects on transfo rmation efficiency of electroporation conditions such as electric-field str ength (2, 4, 6, 8, 10, 12 kV cm(-1)) and time constant (2.5, 5 ms). At a ti me constant of 2.5 ms, few transformants were observed regardless of the fi eld strength. The longer time constant of 5.0 ms reproducibly yielded trans formants at the middle field strength of 4 - 8 kV cm(-1), but gave high kil ling and no transformation at the higher field strength of 10 - 12 kV cm(-1 ). Chloramphenicol acetyltransferase (CAT) activities were increased only i n the transformants from 2-6 kV cm(-1) and 5.0 ms. The density of the trans formants was significantly correlated with the relative value of CAT activi ty (r = 0.89, n = 11, p < 0.01), suggesting that the chloramphenicol resist ance was due to CAT activity. We concluded that transformation of S. platen sis was most effective at a pulse duration 5.0 ms with an electric field of 4 kV cm(-1), and that foreign genes can be expressed in this organism.